Streptococcus

Streptococcus is one of the two medically important genera of gram-positive cocci, the other being Staphylococcus Staphylococcus Staphylococcus is a medically important genera of Gram-positive, aerobic cocci. These bacteria form clusters resembling grapes on culture plates. Staphylococci are ubiquitous for humans, and many strains compose the normal skin flora. Staphylococcus. Streptococci are identified as different species on blood agar on the basis of their hemolytic pattern and sensitivity to optochin and bacitracin. There are many pathogenic species of streptococci, including S. pyogenes, S. agalactiae, S. pneumoniae, and the viridans streptococci (e.g., S. mutans, S. mitis, and S. sanguinis). Streptococcal infections cause a wide array of clinical manifestations, including pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis, pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia, skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin and soft tissue infections, endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis, septicemia, meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis, and streptococcal toxic shock syndrome Toxic Shock Syndrome Toxic shock syndrome (TSS) is an acute, multi-systemic disease caused by the toxin-producing bacteria, Staphylococcus aureus and Streptococcus pyogenes. Staphylococcal TSS is more common and associated with tampons and nasal packing. Toxic Shock Syndrome. They are also responsible for the postinfectious syndromes of acute rheumatic fever Rheumatic fever Acute rheumatic fever (ARF) is an autoimmune inflammatory process that usually follows Streptococcal pharyngitis. Acute rheumatic fever usually occurs 2-4 weeks after an untreated infection and affects the heart, skin, joints, and nervous system. Rheumatic Fever and poststreptococcal glomerulonephritis Poststreptococcal Glomerulonephritis Post-streptococcal glomerulonephritis (PSGN) is a type of nephritis that is caused by a prior infection with group A beta-hemolytic Streptococcus (GAS). The clinical presentation of PSGN can range from asymptomatic, microscopic hematuria to full-blown acute nephritic syndrome, which is characterized by red-to-brown urine, proteinuria, edema, and acute kidney injury. Poststreptococcal Glomerulonephritis. Most streptococci are sensitive to penicillin.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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General Characteristics

Shared characteristics

  • Gram-positive cocci: Some may lose positive staining after overnight incubation or if the culture ages and bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview die.
  • Grow in pairs or chains: Classic long chains are best seen when grown in liquid medium.
  • Nonmotile
  • Non–spore-forming
  • Facultative anaerobes (oxygen tolerant)
  • Catalase negative:
    • Catalase is an enzyme that splits hydrogen peroxide into water and oxygen.
    • The state of being catalase negative is a key finding that differentiates streptococci from staphylococci, which are catalase positive.
  • Habitats: skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin and mucous membranes of humans and animals

Capsule

  • Important virulence factor
  • Encapsulated streptococci:
    • Hyaluronic acid: group A (S. pyogenes)
    • Polysaccharide:
      • Group B (S. agalactiae)
      • S. pneumoniae
      • Group D ( Enterococcus Enterococcus Enterococcus is a genus of oval-shaped gram-positive cocci that are arranged in pairs or short chains. Distinguishing factors include optochin resistance and the presence of pyrrolidonyl arylamidase (PYR) and Lancefield D antigen. Enterococcus is part of the normal flora of the human GI tract. Enterococcus)
  • Nonencapsulated streptococci: 
    • Viridans streptococci 
      • S. viridans is not a true or single species; rather, it is a pseudo-taxonomic term.
      • Represents different groups of streptococci, including the S. bovis group (e.g., S. gallolyticus), S. mitis, the S. mutans group, S. sanguinis, the S. anginosus group, S. constellatus, S. intermedius, and the S. salivarius group.
    • Nonencapsulated S. pneumoniae:
      • Some natural nonencapsulated phenotypes exist and cause disease.
      • Capsular production is lost by all encapsulated pneumococci after passing through a few subcultures on agar, but they will again produce capsules (and have enhanced virulence) if injected into mice.

Biofilm

Streptococci have the ability to form biofilms:

  • Densely packed bacterial communities 
  • Grow on surfaces or human tissues
  • Bacteria secrete and surround themselves with a slimy matrix composed of polymers (polysaccharides in streptococcal species).
  • Examples of biofilms:
    • Dental plaque
    • Bacterial colonization of chronic wounds

Significance:

  • More resistant to host immune defenses
  • More resistant to antibiotics

Differentiation of Streptococcus Species

Microbiology flowchart gram-positive bacteria classification

Gram-positive bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview:
Most bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview can be classified according to a lab procedure called Gram staining.
Bacteria with cell walls that have a thick layer of peptidoglycan retain the crystal violet stain utilized in Gram staining but are not affected by the safranin counterstain. These bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview appear as purple-blue on the stain, indicating that they are gram positive. The bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview can be further classified according to morphology (branching filaments, bacilli, and cocci in clusters or chains) and their ability to grow in the presence of oxygen (aerobic versus anaerobic). The cocci can also be further identified. Staphylococci can be narrowed down on the basis of the presence of the enzyme coagulase and on their sensitivity to the antibiotic novobiocin. Streptococci are grown on blood agar and classified on the basis of which form of hemolysis they employ (α, β, or γ). Streptococci are further narrowed on the basis of their response to the pyrrolidonyl-β-naphthylamide (PYR) test, their sensitivity to specific antimicrobials (optochin and bacitracin), and their ability to grow on sodium chloride (NaCl) media.

Image by Lecturio. License: CC BY-NC-SA 4.0

Serologic (Lancefield) classification

  • Groups A–V are identified on the basis of the antigens in the cell wall, pili, or capsule.
  • Now mostly of historic interest, as many more species have been described
  • Some streptococcal species are still traditionally referred to by their serologic types (groups A, B, and D).
    • Group A: S. pyogenes
    • Group B: S. agalactiae
    • Group C: S. equisimilis, S. equi, S. zooepidemicus
    • Group D: Enterococcus Enterococcus Enterococcus is a genus of oval-shaped gram-positive cocci that are arranged in pairs or short chains. Distinguishing factors include optochin resistance and the presence of pyrrolidonyl arylamidase (PYR) and Lancefield D antigen. Enterococcus is part of the normal flora of the human GI tract. Enterococcus faecalis, E. faecium, E. durans, S. bovis
    • Groups F, G, and L: S. anginosus
    • Group H: S. sanguis
    • Group K: S. salivarius
    • Group L: S. dysgalactiae
    • Groups M and O: S. mitis
    • Group N: Lactococcus lactis
    • Groups R and S: S. suis

Hemolytic classification

Streptococci grow well on blood agar. Streptococcus species are divided into 3 groups on the basis of their hemolysis pattern:

  • β-Hemolytic: complete hemolysis (clear zone of hemolysis):
    • S. pyogenes
    • S. agalactiae
  • α-Hemolytic: partial hemolysis (green zone of hemolysis):
    • S. pneumoniae
    • Viridans streptococci ( variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables hemolytic patterns in some species)
  • γ-Hemolytic: no hemolysis:
    • S. gallolyticus (a member of the S. bovis group)
    • S. faecalis and S. faecium have been reclassified into the distinct genus of Enterococcus Enterococcus Enterococcus is a genus of oval-shaped gram-positive cocci that are arranged in pairs or short chains. Distinguishing factors include optochin resistance and the presence of pyrrolidonyl arylamidase (PYR) and Lancefield D antigen. Enterococcus is part of the normal flora of the human GI tract. Enterococcus as E. faecalis and E. faecium.
Streptococcus pyogenes (lancefield group a) on columbia horse blood agar

Blood agar plate showing β-hemolytic colonies of S. pyogenes:
Note the complete (beta-type) hemolysis around each colony.

Image: “Lancefield Group A” by Nathan Reading. License: CC BY 2.0

Distinguishing factors of the pathogenic streptococci

Distinguishing factors of the pathogenic streptococci
Species Morphology Usual habitat Distinguishing features
S. pyogenes (group A strep) Appear in pairs of chains Throat, skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin
  • Encapsulated by hyaluronic acid
  • β-Hemolytic
  • Inhibited by bacitracin
  • PYR positive
S. agalactiae (group B strep) Appear in pairs or chains Vagina Vagina The vagina is the female genital canal, extending from the vulva externally to the cervix uteri internally. The structures have sexual, reproductive, and urinary functions and a rich blood supply, mainly arising from the internal iliac artery. Vagina, Vulva, and Pelvic Floor, lower gastrointestinal tract
  • Encapsulated by polysaccharide capsule
  • β-Hemolytic
  • Hippurate positive
  • cAMP test positive: Increasing zone of hemolysis when plated with S. aureus
  • Bacitracin resistant
S. pneumoniae Lancet-shaped diplococci Nasopharynx
  • Encapsulated by polysaccharide capsule
  • α-Hemolytic
  • Optochin sensitive
  • Bile soluble: cannot grow in bile
Viridans streptococci: S. mutans, S. mitis, S. sanguinis Appear in pairs or chains Oral cavity, colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix (S. bovis)
  • Nonencapsulated
  • α-Hemolytic
  • Optochin resistant
  • Bile resistant: can grow in bile
Enterococci (formerly group D strep, reclassified as the distinct genus Enterococcus Enterococcus Enterococcus is a genus of oval-shaped gram-positive cocci that are arranged in pairs or short chains. Distinguishing factors include optochin resistance and the presence of pyrrolidonyl arylamidase (PYR) and Lancefield D antigen. Enterococcus is part of the normal flora of the human GI tract. Enterococcus): E. faecalis, E. faecium
S. gallolyticus (in group D and a member of the S. bovis group)
Appear in pairs, short chains, or singly Mostly in intestine, but oral cavity and vagina can be colonized
  • Ɣ-Hemolytic (nonhemolytic)
  • Grow in 6.5% NaCl
PYR: pyrrolidonyl-β-naphthylamide

Pathogenesis

Each pathogenic species of streptococci has key virulence factors that relate to their spread and clinical manifestations. See the charts below for a summary of these features in selected species:

Virulence factors and functions of S. pyogenes (group A strep)
Virulence factors Function
Capsule Inhibits phagocytosis
M protein (involved in rheumatic fever Rheumatic fever Acute rheumatic fever (ARF) is an autoimmune inflammatory process that usually follows Streptococcal pharyngitis. Acute rheumatic fever usually occurs 2-4 weeks after an untreated infection and affects the heart, skin, joints, and nervous system. Rheumatic Fever)
  • Antiphagocytic
  • Molecular mimicry ( type II hypersensitivity reaction Type II hypersensitivity reaction Type II hypersensitivity, also known as antibody-mediated cytotoxic hypersensitivity, is caused by immunoglobulin G (IgG) and IgM antibodies directed against antigens on cells or extracellular materials. The reaction leads to cytotoxic processes involving antibodies and the complement system. Type II Hypersensitivity Reaction) of myosin in heart valves: The mitral valve is affected most often and the aortic valve less commonly.
Streptolysin O Lyses RBCs
Streptokinase ( fibrinolysin Fibrinolysin A product of the lysis of plasminogen (profibrinolysin) by plasminogen activators. It is composed of two polypeptide chains, light (b) and heavy (a), with a molecular weight of 75, 000. It is the major proteolytic enzyme involved in blood clot retraction or the lysis of fibrin and quickly inactivated by antiplasmins. Hemostasis) Converts plasminogen to plasmin Plasmin A product of the lysis of plasminogen (profibrinolysin) by plasminogen activators. It is composed of two polypeptide chains, light (b) and heavy (a), with a molecular weight of 75, 000. It is the major proteolytic enzyme involved in blood clot retraction or the lysis of fibrin and quickly inactivated by antiplasmins. Hemostasis and lyses blood clots, allowing bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview to escape from the clot
DNAse
  • Depolymerizes DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure
  • Aids AIDS Chronic HIV infection and depletion of CD4 cells eventually results in acquired immunodeficiency syndrome (AIDS), which can be diagnosed by the presence of certain opportunistic diseases called AIDS-defining conditions. These conditions include a wide spectrum of bacterial, viral, fungal, and parasitic infections as well as several malignancies and generalized conditions. HIV Infection and AIDS in spread by liquefying pus, which owes its viscosity to DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure (mostly from dead neutrophils)
Hyaluronidase Aids AIDS Chronic HIV infection and depletion of CD4 cells eventually results in acquired immunodeficiency syndrome (AIDS), which can be diagnosed by the presence of certain opportunistic diseases called AIDS-defining conditions. These conditions include a wide spectrum of bacterial, viral, fungal, and parasitic infections as well as several malignancies and generalized conditions. HIV Infection and AIDS in spread by splitting hyaluronic acid, an important component of the ground substance of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue
Lipoteichoic acid (covers hairlike pili that project through capsule) Adhere to epithelial cells
3 types of streptococcal pyrogenic exotoxins:
  • SpeA: involved in scarlet fever Scarlet fever Scarlet fever is a clinical syndrome consisting of streptococcal pharyngitis accompanied by fever and a characteristic rash caused by pyrogenic exotoxins. Scarlet fever is a non-suppurative complication of streptococcal infection that is more commonly seen in children. Incidence peaks during the winter and spring in temperate climates. Scarlet Fever and streptococcal toxic shock syndrome Toxic Shock Syndrome Toxic shock syndrome (TSS) is an acute, multi-systemic disease caused by the toxin-producing bacteria, Staphylococcus aureus and Streptococcus pyogenes. Staphylococcal TSS is more common and associated with tampons and nasal packing. Toxic Shock Syndrome
  • SpeB: protease, involved in poststreptococcal glomerulonephritis Poststreptococcal Glomerulonephritis Post-streptococcal glomerulonephritis (PSGN) is a type of nephritis that is caused by a prior infection with group A beta-hemolytic Streptococcus (GAS). The clinical presentation of PSGN can range from asymptomatic, microscopic hematuria to full-blown acute nephritic syndrome, which is characterized by red-to-brown urine, proteinuria, edema, and acute kidney injury. Poststreptococcal Glomerulonephritis (bacterial infection-related glomerulonephritis)
  • SpeC: involved in scarlet fever Scarlet fever Scarlet fever is a clinical syndrome consisting of streptococcal pharyngitis accompanied by fever and a characteristic rash caused by pyrogenic exotoxins. Scarlet fever is a non-suppurative complication of streptococcal infection that is more commonly seen in children. Incidence peaks during the winter and spring in temperate climates. Scarlet Fever and streptococcal toxic shock syndrome Toxic Shock Syndrome Toxic shock syndrome (TSS) is an acute, multi-systemic disease caused by the toxin-producing bacteria, Staphylococcus aureus and Streptococcus pyogenes. Staphylococcal TSS is more common and associated with tampons and nasal packing. Toxic Shock Syndrome
SpeA and SpeC are called superantigens because they stimulate T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells to produce cytokines by binding to the V-beta region of the T-cell receptor.
  • In scarlet fever Scarlet fever Scarlet fever is a clinical syndrome consisting of streptococcal pharyngitis accompanied by fever and a characteristic rash caused by pyrogenic exotoxins. Scarlet fever is a non-suppurative complication of streptococcal infection that is more commonly seen in children. Incidence peaks during the winter and spring in temperate climates. Scarlet Fever: Blood vessels are dilated because the cutaneous cytokine milieu is altered.
  • In toxic shock syndrome Toxic Shock Syndrome Toxic shock syndrome (TSS) is an acute, multi-systemic disease caused by the toxin-producing bacteria, Staphylococcus aureus and Streptococcus pyogenes. Staphylococcal TSS is more common and associated with tampons and nasal packing. Toxic Shock Syndrome: The overwhelming release of inflammatory cytokines by T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells mediates shock.
  • In poststreptococcal glomerulonephritis Poststreptococcal Glomerulonephritis Post-streptococcal glomerulonephritis (PSGN) is a type of nephritis that is caused by a prior infection with group A beta-hemolytic Streptococcus (GAS). The clinical presentation of PSGN can range from asymptomatic, microscopic hematuria to full-blown acute nephritic syndrome, which is characterized by red-to-brown urine, proteinuria, edema, and acute kidney injury. Poststreptococcal Glomerulonephritis: Antigen–antibody complexes form on the glomerular basement membrane. The two most important group A strep antigens are SpeB and nephritis-associated plasmin Plasmin A product of the lysis of plasminogen (profibrinolysin) by plasminogen activators. It is composed of two polypeptide chains, light (b) and heavy (a), with a molecular weight of 75, 000. It is the major proteolytic enzyme involved in blood clot retraction or the lysis of fibrin and quickly inactivated by antiplasmins. Hemostasis receptor.
2 types of hemolysins:
  • Streptolysin O: stimulates production of antibody anti–streptolysin O (ASO); inactivated by oxygen
  • Streptolysin S: not antigenic
Lyse RBCs and also damage the membranes of other cells
Spe: Streptococcal pyrogenic exotoxins
Virulence factors and functions of S. agalactiae (group B strep)
Virulence factors Function
Capsule Inhibits phagocytosis
Virulence factors and functions of S. pneumoniae
Virulence factors Function
Capsule Inhibits phagocytosis
IgA protease Mucosal invasion
Virulence factors and functions of S. mutans
Virulence factors Function
Dextrans Platelet adhesion
In vivo biofilm production Adhesion

Diseases Caused by β-Hemolytic Streptococci

Streptococcus pyogenes

Streptococcus pyogenes is the most virulent pathogen in the Streptococcus family.

Pharyngitis:

  • Most common infection caused by S. pyogenes 
  • In infants and small children: subacute nasopharyngitis, palatal petechiae, cervical lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy; may lead to middle-ear infection
  • In older children and adults: intense nasopharyngitis, tonsillitis Tonsillitis Tonsillitis is inflammation of the pharynx or pharyngeal tonsils, and therefore is also called pharyngitis. An infectious etiology in the setting of tonsillitis is referred to as infectious pharyngitis, which is caused by viruses (most common), bacteria, or fungi. Tonsillitis, purulent exudates, high fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, cervical lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy
  • Asymptomatic infections: 20%
  • Many other etiologies of pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis: adenovirus Adenovirus Adenovirus (member of the family Adenoviridae) is a nonenveloped, double-stranded DNA virus. Adenovirus is transmitted in a variety of ways, and it can have various presentations based on the site of entry. Presentation can include febrile pharyngitis, conjunctivitis, acute respiratory disease, atypical pneumonia, and gastroenteritis. Adenovirus, infectious mononucleosis Mononucleosis Infectious mononucleosis (IM), also known as "the kissing disease," is a highly contagious viral infection caused by the Epstein-Barr virus. Its common name is derived from its main method of transmission: the spread of infected saliva via kissing. Clinical manifestations of IM include fever, tonsillar pharyngitis, and lymphadenopathy. Mononucleosis, gonococcal infection, diphtheria Diphtheria Diphtheria is an infectious disease caused by Corynebacterium diphtheriae that most often results in respiratory disease with membranous inflammation of the pharynx, sore throat, fever, swollen glands, and weakness. The hallmark sign is a sheet of thick, gray material covering the back of the throat. Diphtheria
Streptococcal pharyngitis

Streptococcal pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis:
Redness and edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema of the throat and palatal petechiae

Image: “Streptococcal pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis” by CDC/Dr. Heinz F. Eichenwald. License: Public Domain

Skin and soft tissue infections:

  • Impetigo Impetigo Impetigo is a highly contagious superficial bacterial infection typically caused by Staphylococcus aureus (most common) and Streptococcus pyogenes. Impetigo most commonly presents in children aged 2 to 5 years with lesions that evolve from papules to vesicles to pustules, which eventually break down to form characteristic "honey-colored" crusts. Impetigo
    • “Honey-crusted” skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin lesions
    • Mostly affects children 2–5 years of age
    • Highly communicable, especially in hot, humid climates
    • May progress to cellulitis Cellulitis Cellulitis is a common infection caused by bacteria that affects the dermis and subcutaneous tissue of the skin. It is frequently caused by Staphylococcus aureus and Streptococcus pyogenes. The skin infection presents as an erythematous and edematous area with warmth and tenderness. Cellulitis
    • May also be caused by Staphylococcus Staphylococcus Staphylococcus is a medically important genera of Gram-positive, aerobic cocci. These bacteria form clusters resembling grapes on culture plates. Staphylococci are ubiquitous for humans, and many strains compose the normal skin flora. Staphylococcus aureus
  • Erysipelas Erysipelas Erysipelas is a bacterial infection of the superficial layer of the skin extending to the skin's superficial lymphatic vessels. This infection presents as a raised, well-defined, tender, and bright red rash. Typically on the legs or face, but erysipelas can occur anywhere on the skin. Erysipelas
    • Infection of upper dermis and superficial lymphatics
    • Red, raised, rapidly advancing, and well-demarcated margin of infection (being raised and well demarcated differentiates it from cellulitis Cellulitis Cellulitis is a common infection caused by bacteria that affects the dermis and subcutaneous tissue of the skin. It is frequently caused by Staphylococcus aureus and Streptococcus pyogenes. The skin infection presents as an erythematous and edematous area with warmth and tenderness. Cellulitis)
  • Cellulitis: 
    • Infection of deep dermis and subcutaneous fat
    • Red, not raised, and not well-demarcated margin of infection (not being raised and not being well demarcated differentiates it from erysipelas)
  • Abscess: 
    • Localized collection of pus in a newly created cavity
    • S. pyogenes and Staphylococcus Staphylococcus Staphylococcus is a medically important genera of Gram-positive, aerobic cocci. These bacteria form clusters resembling grapes on culture plates. Staphylococci are ubiquitous for humans, and many strains compose the normal skin flora. Staphylococcus aureus (MRSA) are the most common causes of abscesses on the trunk, extremities, axillae, or head and neck.
  • Necrotizing fasciitis Necrotizing fasciitis Necrotizing fasciitis is a life-threatening infection that causes rapid destruction and necrosis of the fascia and subcutaneous tissues. Patients may present with significant pain out of proportion to the presenting symptoms and rapidly progressive erythema of the affected area. Necrotizing Fasciitis (“flesh-eating bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview” or “streptococcal gangrene”)
    • A necrotizing soft tissue infection [NSTI] that also includes necrotizing forms of myositis and cellulitis Cellulitis Cellulitis is a common infection caused by bacteria that affects the dermis and subcutaneous tissue of the skin. It is frequently caused by Staphylococcus aureus and Streptococcus pyogenes. The skin infection presents as an erythematous and edematous area with warmth and tenderness. Cellulitis  
    • Fulminant tissue destruction, systemic signs of toxicity, and high mortality; usually polymicrobial, with aerobic and anaerobic bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview
    • Overlying skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin may seem only mildly warm, with no clear portal of entry.
    • Predisposing factors: diabetes, trauma, immunosuppression
    • Pyrogenic exotoxins most likely contribute to shock via cytokines.
    • Surgical emergency: debridement and administration of antibiotics urgently needed
Impetigo on face of a child

Impetigo Impetigo Impetigo is a highly contagious superficial bacterial infection typically caused by Staphylococcus aureus (most common) and Streptococcus pyogenes. Impetigo most commonly presents in children aged 2 to 5 years with lesions that evolve from papules to vesicles to pustules, which eventually break down to form characteristic "honey-colored" crusts. Impetigo in a child:
The image shows characteristic “honey-crusted” lesions around the mouth.

Image: “Microbio 21 02 impetigo” by CNX OpenStax. License: CC BY 4.0

Puerperal fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever: occurs when S. pyogenes enters uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Posterior Abdominal Wall after delivery, causing  endometritis Endometritis Endometritis is an inflammation of the endometrium, the inner layer of the uterus. The most common subtype is postpartum endometritis, resulting from the ascension of normal vaginal flora to the previously aseptic uterus. Endometritis and bacteremia

Bacteremia or sepsis Sepsis Organ dysfunction resulting from a dysregulated systemic host response to infection separates sepsis from uncomplicated infection. The etiology is mainly bacterial and pneumonia is the most common known source. Patients commonly present with fever, tachycardia, tachypnea, hypotension, and/or altered mentation. Sepsis and Septic Shock caused by:

  • Infected traumatic or surgical wounds
  • Skin infections (e.g., cellulitis Cellulitis Cellulitis is a common infection caused by bacteria that affects the dermis and subcutaneous tissue of the skin. It is frequently caused by Staphylococcus aureus and Streptococcus pyogenes. The skin infection presents as an erythematous and edematous area with warmth and tenderness. Cellulitis)
  • Pharyngitis (rare)

Toxin-mediated diseases

Scarlet fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever:

  • Usually in association with pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis
  • Mediated by toxins (superantigen A or C) 
  • Diffuse papular erythematous rash; palms, soles, and face usually spared
  • “Strawberry tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Oral Cavity: Lips and Tongue
  • Circumoral pallor
Scarlet fever rash

Rash of scarlet fever Scarlet fever Scarlet fever is a clinical syndrome consisting of streptococcal pharyngitis accompanied by fever and a characteristic rash caused by pyrogenic exotoxins. Scarlet fever is a non-suppurative complication of streptococcal infection that is more commonly seen in children. Incidence peaks during the winter and spring in temperate climates. Scarlet Fever

Image: “The rash of scarlet fever Scarlet fever Scarlet fever is a clinical syndrome consisting of streptococcal pharyngitis accompanied by fever and a characteristic rash caused by pyrogenic exotoxins. Scarlet fever is a non-suppurative complication of streptococcal infection that is more commonly seen in children. Incidence peaks during the winter and spring in temperate climates. Scarlet Fever” by Alicia Williams. License: CC BY 2.5

Toxic shock syndrome ( TSS TSS Toxic shock syndrome (TSS) is an acute, multi-systemic disease caused by the toxin-producing bacteria, Staphylococcus aureus and Streptococcus pyogenes. Staphylococcal TSS is more common and associated with tampons and nasal packing. Toxic Shock Syndrome):

  • Early-onset shock, bacteremia, respiratory failure Respiratory failure Respiratory failure is a syndrome that develops when the respiratory system is unable to maintain oxygenation and/or ventilation. Respiratory failure may be acute or chronic and is classified as hypoxemic, hypercapnic, or a combination of the two. Respiratory Failure, and multiorgan failure
  • Fatal in 30% of cases
  • May be preceded by minor trauma with local signs of infection
  • Mediated by superantigen toxins
  • Toxic shock syndrome can also be caused by Staphylococcus Staphylococcus Staphylococcus is a medically important genera of Gram-positive, aerobic cocci. These bacteria form clusters resembling grapes on culture plates. Staphylococci are ubiquitous for humans, and many strains compose the normal skin flora. Staphylococcus aureus, which can also express superantigen toxins.

Postinfectious sequelae

Rheumatic fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever:

  • 2–3 weeks after pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis
  • Early antibiotic treatment of pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis decreases the incidence.
  • Associated with antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins to streptolysin O, hyaluronidase, and streptokinase
  • J♡NES criteria:
    • Joint involvement (polyarthritis)
    • (mitral valve stenosis, myocarditis Myocarditis Myocarditis is an inflammatory disease of the myocardium, which may occur alone or in association with a systemic process. There are numerous etiologies of myocarditis, but all lead to inflammation and myocyte injury, most often leading to signs and symptoms of heart failure. Myocarditis, pericarditis Pericarditis Pericarditis is an inflammation of the pericardium, often with fluid accumulation. It can be caused by infection (often viral), myocardial infarction, drugs, malignancies, metabolic disorders, autoimmune disorders, or trauma. Acute, subacute, and chronic forms exist. Pericarditis)
    • Nodules (subcutaneous; on extensor surfaces)
    • Erythema marginatum (rash)
    • Sydenham’s chorea (neurologic)

Poststreptococcal glomerulonephritis ( PSGN PSGN Post-streptococcal glomerulonephritis (PSGN) is a type of nephritis that is caused by a prior infection with group A beta-hemolytic Streptococcus (GAS). The clinical presentation of PSGN can range from asymptomatic, microscopic hematuria to full-blown acute nephritic syndrome, which is characterized by red-to-brown urine, proteinuria, edema, and acute kidney injury. Poststreptococcal Glomerulonephritis):

  • Caused by specific nephritogenic strains that have the 2 most important antigens (SpeB and nephritis-associated plasmin Plasmin A product of the lysis of plasminogen (profibrinolysin) by plasminogen activators. It is composed of two polypeptide chains, light (b) and heavy (a), with a molecular weight of 75, 000. It is the major proteolytic enzyme involved in blood clot retraction or the lysis of fibrin and quickly inactivated by antiplasmins. Hemostasis receptor)
  • Occurs 2–3 weeks after pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis or impetigo
  • Deposition of immune complexes within glomerular basement membrane (type 3 hypersensitivity reaction)
  • Hematuria/proteinuria, edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema, hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
  • Usually (but not always) benign and self-limited

Streptococcus agalactiae: The Group B Streptococci (GBS)

  • Frequently colonize genital (in 5%–30% of women) and GI tracts 
  • In older adults with chronic medical conditions:
    • Most common infection: cellulitis Cellulitis Cellulitis is a common infection caused by bacteria that affects the dermis and subcutaneous tissue of the skin. It is frequently caused by Staphylococcus aureus and Streptococcus pyogenes. The skin infection presents as an erythematous and edematous area with warmth and tenderness. Cellulitis
    • Sepsis
    • Less common: cystitis, pyelonephritis Pyelonephritis Pyelonephritis is infection affecting the renal pelvis and the renal parenchyma. This condition arises mostly as a complication of bladder infection that ascends to the upper urinary tract. Pyelonephritis can be acute or chronic (which results from persistent or chronic infections). Typical acute symptoms are flank pain, fever, and nausea with vomiting. T Pyelonephritis and Perinephric Abscess, pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia, septic arthritis Septic arthritis Septic arthritis is an infection of the joint due to direct inoculation, contiguous extension, or hematogenous spread of infectious organisms into the joint space. This process causes an acute, inflammatory, monoarticular arthritis. Septic Arthritis, endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis, meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis
  • In pregnant women:
    • Urinary tract infection (or asymptomatic bacteriuria)
    • Chorioamnionitis Chorioamnionitis Chorioamnionitis, commonly referred to as intraamniotic infection (IAI), is a common obstetric complication involving infection and inflammation of the fetal membranes, amniotic fluid, placenta, or the fetus itself. Chorioamnionitis is typically caused by a polymicrobial infection that ascends from the lower genitourinary tract. Chorioamnionitis
    • Postpartum endometritis Endometritis Endometritis is an inflammation of the endometrium, the inner layer of the uterus. The most common subtype is postpartum endometritis, resulting from the ascension of normal vaginal flora to the previously aseptic uterus. Endometritis
  • In neonates:
    • Acquired in utero by ascending infection or during passage through vagina
    • Early (within 6 days) or late (up to 90 days) onset
    • Can present with:
      • Bacteremia (without focus)
      • Sepsis
      • Meningitis
      • Pneumonia
      • Respiratory distress syndrome

Diseases Caused by α-Hemolytic Streptococci

Streptococcus pneumoniae

  • Most common bacterial cause of community-acquired pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia
    • Presents with hypoxia, cough, tachypnea, tachycardia, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever
    • Human-to-human transmission by aerosols or close contact
  • Nasopharyngeal colonization is common (5%–40%). Aspiration of nasopharyngeal secretions into the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs can lead to pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia if:
    • Very large bacterial inoculum
    • Normal clearance mechanisms impaired by smoking, viral infections, alcohol or drug intoxication, systemic illness, heart failure
  • Can also spread and cause bacteremia, which can result in bacterial seeding of other organs:
    • CNS: meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis, otitis media, 
    • Cardiac: endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis, pericarditis Pericarditis Pericarditis is an inflammation of the pericardium, often with fluid accumulation. It can be caused by infection (often viral), myocardial infarction, drugs, malignancies, metabolic disorders, autoimmune disorders, or trauma. Acute, subacute, and chronic forms exist. Pericarditis
    • Rheumatic: septic arthritis Septic arthritis Septic arthritis is an infection of the joint due to direct inoculation, contiguous extension, or hematogenous spread of infectious organisms into the joint space. This process causes an acute, inflammatory, monoarticular arthritis. Septic Arthritis, osteomyelitis Osteomyelitis Osteomyelitis is an infection of the bone that results from the spread of microorganisms from the blood (hematogenous), nearby infected tissue, or open wounds (non-hematogenous). Infections are most commonly caused by Staphylococcus aureus. Osteomyelitis
Endocarditis ultrasound

Infective endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis:
A bacterial vegetation (arrow) is seen on the tricuspid valve on an echocardiogram.

Image: “Endocarditis ultrasound” by Daisuke Koya et al. License: CC BY 2.0

Viridans Streptococci

  • Most prevalent bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview of the normal microbiota of the upper respiratory tract
  • Important for the healthy state of the mucous membranes
  • Most commonly get into the bloodstream through breaks in oral mucosa (e.g., during dental procedures)
  • Have been associated with:
    • Sinusitis Sinusitis Sinusitis refers to inflammation of the mucosal lining of the paranasal sinuses. The condition usually occurs concurrently with inflammation of the nasal mucosa (rhinitis), a condition known as rhinosinusitis. Acute sinusitis is due to an upper respiratory infection caused by a viral, bacterial, or fungal agent. Sinusitis in immunocompromised patients
    • S. mutans: dental caries, endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis
    • S. mitis: endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis, bacteremia, high level of resistance to penicillin
    • S. bovis: endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis, biliary disease, common blood isolate in colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix cancer
    • S. anginosus group: pyogenic infections in brain, liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver, lung
    • S. salivarius group: bacteremia, endocarditis Endocarditis Endocarditis is an inflammatory disease involving the inner lining (endometrium) of the heart, most commonly affecting the cardiac valves. Both infectious and noninfectious etiologies lead to vegetations on the valve leaflets. Patients may present with nonspecific symptoms such as fever and fatigue. Endocarditis, meningitis Meningitis Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Meningitis

Enterococci

  • Reclassified into their own genus, Enterococcus Enterococcus Enterococcus is a genus of oval-shaped gram-positive cocci that are arranged in pairs or short chains. Distinguishing factors include optochin resistance and the presence of pyrrolidonyl arylamidase (PYR) and Lancefield D antigen. Enterococcus is part of the normal flora of the human GI tract. Enterococcus
  • Very similar to Streptococcus in physical appearance and characteristics
  • Commensal organisms in human intestines
  • Have been associated with:
    • Urinary tract infections Urinary tract infections Urinary tract infections (UTIs) represent a wide spectrum of diseases, from self-limiting simple cystitis to severe pyelonephritis that can result in sepsis and death. Urinary tract infections are most commonly caused by Escherichia coli, but may also be caused by other bacteria and fungi. Urinary Tract Infections
    • Diverticulitis
    • Spontaneous bacterial peritonitis
    • Endocarditis (commonly after manipulation of GI or urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract)
    • Meningitis (rare)

Identification and Prevention

Identification and prevention
Species Identification Prevention
S. pyogenes Group A strep (GAS)
  • Gram stain (cannot differentiate from a viridans streptococcus)
  • Rapid streptococcal antigen test (“strep test”): specificity high, but sensitivity 77%–92%
  • Throat culture: 24–48 hours
  • Beta-hemolysis
  • PCR PCR Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. Polymerase Chain Reaction (PCR) testing: not always available
  • ASO titer, anti-DNAse titer: if rheumatic fever Rheumatic fever Acute rheumatic fever (ARF) is an autoimmune inflammatory process that usually follows Streptococcal pharyngitis. Acute rheumatic fever usually occurs 2-4 weeks after an untreated infection and affects the heart, skin, joints, and nervous system. Rheumatic Fever or acute poststreptococcal glomerulonephritis Poststreptococcal Glomerulonephritis Post-streptococcal glomerulonephritis (PSGN) is a type of nephritis that is caused by a prior infection with group A beta-hemolytic Streptococcus (GAS). The clinical presentation of PSGN can range from asymptomatic, microscopic hematuria to full-blown acute nephritic syndrome, which is characterized by red-to-brown urine, proteinuria, edema, and acute kidney injury. Poststreptococcal Glomerulonephritis is suspected
Early (before day 8) antibiotic treatment of pharyngitis Pharyngitis Pharyngitis is an inflammation of the back of the throat (pharynx). Pharyngitis is usually caused by an upper respiratory tract infection, which is viral in most cases. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and hoarseness. Pharyngitis to prevent rheumatic fever Rheumatic fever Acute rheumatic fever (ARF) is an autoimmune inflammatory process that usually follows Streptococcal pharyngitis. Acute rheumatic fever usually occurs 2-4 weeks after an untreated infection and affects the heart, skin, joints, and nervous system. Rheumatic Fever (RF) and continued chemoprophylaxis for years in persons who have had an attack of RF to prevent relapse of RF activity
S. agalactiae group B strep (GBS)
  • PCR PCR Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. Polymerase Chain Reaction (PCR)-based tests on urine
  • Cultures: beta-hemolysis and biochemical testing
Screen all pregnant women at 35–37 weeks for GBS and administer IV antibiotics (penicillin) during labor Labor Labor is the normal physiologic process defined as uterine contractions resulting in dilatation and effacement of the cervix, which culminates in expulsion of the fetus and the products of conception. Normal and Abnormal Labor to prevent neonatal infection
S. pneumoniae
  • Sputum Gram stain and culture
  • Blood culture: alpha-hemolysis, then biochemical testing, molecular testing, or a mass spectrometry method
Immunization, following U.S. Advisory Committee on Immunization Practices (ACIP) guidelines for different ages and medical conditions, with:
  • Pneumococcal conjugate vaccine Vaccine A vaccine is usually an antigenic, non-virulent form of a normally virulent microorganism. Vaccinations are a form of primary prevention and are the most effective form due to their safety, efficacy, low cost, and easy access. Vaccination (Prevnar 13)
  • Pneumococcal polysaccharide vaccine Vaccine A vaccine is usually an antigenic, non-virulent form of a normally virulent microorganism. Vaccinations are a form of primary prevention and are the most effective form due to their safety, efficacy, low cost, and easy access. Vaccination (Pneumovax 23)
Viridans streptococci: S. mutans, S. bovis, S. mitis Blood cultures, then biochemical testing (often unreliable for viridans species, so molecular testing or a mass spectrometry method increasingly being used) Prophylactic antibiotics in patients with high-risk conditions (e.g., prosthetic heart valves, unrepaired cyanotic congenital heart disease) who are undergoing a dental procedure
Enterococcus Enterococcus Enterococcus is a genus of oval-shaped gram-positive cocci that are arranged in pairs or short chains. Distinguishing factors include optochin resistance and the presence of pyrrolidonyl arylamidase (PYR) and Lancefield D antigen. Enterococcus is part of the normal flora of the human GI tract. Enterococcus Cultures (growth in 6.5% NaCl), then biochemical testing, molecular testing, or mass spectrometry methods

References

  1. Group A Streptococcal Disease (GAS). Centers for Disease Control and Prevention. Accessed December 27, 2020.
  2. Haslam DB, St Gemelli JW (2018). Viridans Streptococci, Abiotrophia and Granulicatella Species, and Streptococcus bovis Group. Retrieved December 27, 2020, from https://www.sciencedirect.com/topics/medicine-and-dentistry/viridans-streptococci
  3. Patterson MJ (1996). Streptococcus. Retrieved December 26, 2020, from https://www.ncbi.nlm.nih.gov/books/NBK7611/
  4. Puopolo KM, Baker CJ (2019). Group B streptococcal infection in neonates and young infants. Retrieved December 26, 2020, from https://www.uptodate.com/contents/group-b-streptococcal-infection-in-neonates-and-young-infants
  5. Stevens DL (2020). Invasive group A streptococcal infection and toxic shock syndrome: Epidemiology, clinical manifestations, and diagnosis. Retrieved December 26, 2020, from https://www.uptodate.com/contents/invasive-group-a-streptococcal-infection-and-toxic-shock-syndrome-epidemiology-clinical-manifestations-and-diagnosis
  6. Tuomanen EI (2019). Microbiology and pathogenesis of Streptococcus pneumoniae. Retrieved December 26, 2020, from https://www.uptodate.com/contents/microbiology-and-pathogenesis-of-streptococcus-pneumoniae
  7. Wald ER (2020). Group A streptococcal tonsillopharyngitis in children and adolescents: Clinical features and diagnosis. Retrieved 26 December 2020, from https://www.uptodate.com/contents/group-a-streptococcal-tonsillopharyngitis-in-children-and-adolescents-clinical-features-and-diagnosis
  8. Martin CS, Bradshaw JL, Pipkins HR, McDaniel LS (2018). Pulmonary disease associated with nonencapsulated streptococcus pneumoniae. Open Forum Infectious Diseases. 2018;5(7). https://doi.org/10.1093/ofid/ofy135
  9. Riedel S, Hobden JA (2019). In Riedel, S, Morse, S.A., Mietzner, T., Miller, S. (Eds.), Jawetz, Melnick, & Adelberg’s Medical Microbiology (28th ed., pp. 215-233).
  10. Advisory Committee on Immunization Practices (ACIP). CDC. (2020, December 22). https://www.cdc.gov/vaccines/acip/index.html

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