Shigella is a genus of gram-negative, non-lactose-fermenting facultative intracellular Facultative intracellular Yersinia spp./Yersiniosis bacilli. Infection spreads most commonly via person-to-person contact or through contaminated food and water. Humans are the only known reservoir Reservoir Animate or inanimate sources which normally harbor disease-causing organisms and thus serve as potential sources of disease outbreaks. Reservoirs are distinguished from vectors (disease vectors) and carriers, which are agents of disease transmission rather than continuing sources of potential disease outbreaks. Humans may serve both as disease reservoirs and carriers. Escherichia coli. Because it is resistant to acid, Shigella spp. survive transit through the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy; thus, only a small amount of inoculum is needed to cause disease. Shigellosis (Shigella dysentery Dysentery Acute inflammation of the intestine associated with infectious diarrhea of various etiologies, generally acquired by eating contaminated food containing toxins, biological derived from bacteria or other microorganisms. Dysentery is characterized initially by watery feces then by bloody mucoid stools. It is often associated with abdominal pain; fever; and dehydration. Gastroenteritis) results in 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, abdominal pain Abdominal Pain Acute Abdomen, and bloody diarrhea Bloody diarrhea Diarrhea, which are effects of the toxins and epithelial-cell invasion of the organism. In the majority of cases, symptoms resolve within a few days. However, complications of dehydration Dehydration The condition that results from excessive loss of water from a living organism. Volume Depletion and Dehydration, hemolytic uremic syndrome Hemolytic uremic syndrome A syndrome that is associated with microvascular diseases of the kidney, such as renal cortical necrosis. It is characterized by hemolytic anemia; thrombocytopenia; and acute renal failure. Hypocoagulable Conditions, toxic megacolon Toxic megacolon An acute form of megacolon, severe pathological dilatation of the colon. It is associated with clinical conditions such as ulcerative colitis; Crohn disease; amebic dysentery; or Clostridium enterocolitis. Megacolon, or reactive arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis can arise. Treatment is primarily using fluid and electrolyte replacement and antibiotics.
Last updated: 16 Feb, 2021
Gram-negative
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:
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 can be classified according to a lab procedure called
Gram staining
Gram staining
Bacteriology.
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 with cell walls that have a thin layer of
peptidoglycan
Peptidoglycan
Penicillins do not retain the crystal violet stain utilized in
Gram staining
Gram staining
Bacteriology. 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 do, however, retain the safranin counterstain and thus appear as pinkish-red on the stain, making them
gram negative
Gram negative
Bacteria which lose crystal violet stain but are stained pink when treated by gram’s method.
Yersinia spp./Yersiniosis. 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 can be further classified according to morphology (diplococci, curved rods, bacilli, and coccobacilli) and their ability to grow in the presence of oxygen (aerobic versus anaerobic). 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 can be more narrowly identified by growing them on specific media (triple sugar
iron
Iron
A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen.
Trace Elements (TSI) agar) where their
enzymes
Enzymes
Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules.
Basics of Enzymes can be identified (
urease
Urease
An enzyme that catalyzes the conversion of urea and water to carbon dioxide and ammonia.
Nocardia/Nocardiosis,
oxidase
Oxidase
Neisseria) and their ability to ferment lactose can be tested.
* Stains poorly on
Gram stain
Gram stain
Klebsiella
**
Pleomorphic
Pleomorphic
Bacteroides rod/coccobacillus
*** Require special transport media
Serogroups defined by specific O antigens:
To help remember the modes of transmission of Shigella, remember the “4 Fs:”
Invasion and cell-to-cell spread by Shigella:
1. Pathogen invades and is engulfed by the M cell (transcytosis).
2. Pathogen reaches
subepithelial
Subepithelial
Membranoproliferative Glomerulonephritis
macrophages
Macrophages
The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood monocytes. Main types are peritoneal macrophages; alveolar macrophages; histiocytes; kupffer cells of the liver; and osteoclasts. They may further differentiate within chronic inflammatory lesions to epithelioid cells or may fuse to form foreign body giant cells or langhans giant cells.
Innate Immunity: Phagocytes and Antigen Presentation and
dendritic cells
Dendritic cells
Specialized cells of the hematopoietic system that have branch-like extensions. They are found throughout the lymphatic system, and in non-lymphoid tissues such as skin and the epithelia of the intestinal, respiratory, and reproductive tracts. They trap and process antigens, and present them to T-cells, thereby stimulating cell-mediated immunity. They are different from the non-hematopoietic follicular dendritic cells, which have a similar morphology and immune system function, but with respect to humoral immunity (antibody production).
Skin: Structure and Functions, then induces macrophage
apoptosis
Apoptosis
A regulated cell death mechanism characterized by distinctive morphologic changes in the nucleus and cytoplasm, including the endonucleolytic cleavage of genomic DNA, at regularly spaced, internucleosomal sites, I.e., DNA fragmentation. It is genetically-programmed and serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth.
Ischemic Cell Damage. Shigella sp. is released along with
interleukin-1
Interleukin-1
A soluble factor produced by monocytes; macrophages, and other cells which activates T-lymphocytes and potentiates their response to mitogens or antigens. Interleukin-1 is a general term refers to either of the two distinct proteins, interleukin-1alpha and interleukin-1beta. The biological effects of il-1 include the ability to replace macrophage requirements for t-cell activation.
Interleukins (IL-1) and other
cytokines
Cytokines
Non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner.
Adaptive Immune Response. The pathogen is then engulfed into the adjacent epithelial cell in a membrane-bound compartment (epithelial-cell entry).
3. Released
interleukins
Interleukins
Interleukins are a type of cytokines (signaling proteins) that communicate messages between different parts of the immune system. The majority of interleukins are synthesized by helper CD4 T lymphocytes along with other cells such as monocytes, macrophages, and endothelial cells.
Interleukins also recruit polymorphonuclear
leukocytes
Leukocytes
White blood cells. These include granular leukocytes (basophils; eosinophils; and neutrophils) as well as non-granular leukocytes (lymphocytes and monocytes).
White Myeloid Cells: Histology (PMNs), which destabilize the cellular junctions. This is another entryway for the pathogen (PMN
transmigration
Transmigration
Leukocyte Adhesion Deficiency Type 1).
4. Shigella sp. passes through the disrupted
tight junctions
Tight junctions
Cell-cell junctions that seal adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other.
The Cell: Cell Junctions and then the pathogen enters the epithelial cell. Once inside, the host cell
actin
Actin
Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle.
Skeletal Muscle Contraction nucleators are hijacked.
Actin
Actin
Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle.
Skeletal Muscle Contraction-based
motility
Motility
The motor activity of the gastrointestinal tract.
Gastrointestinal Motility (ABM;
actin
Actin
Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle.
Skeletal Muscle Contraction tail) propels the pathogen to reach the
plasma membrane
Plasma membrane
A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules.
The Cell: Cell Membrane, where the infected cell contacts another cell.
5. Multiplication and intercellular spread are facilitated by cellular protrusion (with Shigella) and
elongation
Elongation
Polymerase Chain Reaction (PCR) into the adjacent cell. The protrusion resolves as a double-membrane vacuole. The pathogen lyses the membrane, escapes, and enters the adjacent cell. The adjacent cell is infected and this process is repeated in other cells.
6. As each invaded epithelial cell dies, fluids are lost.
Shigellosis (“Shigella dysentery Dysentery Acute inflammation of the intestine associated with infectious diarrhea of various etiologies, generally acquired by eating contaminated food containing toxins, biological derived from bacteria or other microorganisms. Dysentery is characterized initially by watery feces then by bloody mucoid stools. It is often associated with abdominal pain; fever; and dehydration. Gastroenteritis”): Stool sample from a patient with shigellosis ( diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea with bloody stools, 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, and abdominal cramps Cramps Ion Channel Myopathy). Shigella seen as rods in the smear
Image: “Shigella stool” by Centers for Disease Control and Prevention Public Health Image Library. License: Public DomainShigella on Hektoen enteric (HE) agar: Colonies of S. boydii grown on HE agar have a raised, green, and moist appearance.
Image: “Shigella boydii 01” by CDC. License: Public DomainShigella and Salmonella Salmonella Salmonellae are gram-negative bacilli of the family Enterobacteriaceae. Salmonellae are flagellated, non-lactose-fermenting, and hydrogen sulfide-producing microbes. Salmonella enterica, the most common disease-causing species in humans, is further classified based on serotype as typhoidal (S. typhi and paratyphi) and nontyphoidal (S. enteritidis and typhimurium). Salmonella invade the gastrointestinal tract, causing diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea.
Shigella | Salmonella Salmonella Salmonellae are gram-negative bacilli of the family Enterobacteriaceae. Salmonellae are flagellated, non-lactose-fermenting, and hydrogen sulfide-producing microbes. Salmonella enterica, the most common disease-causing species in humans, is further classified based on serotype as typhoidal (S. typhi and paratyphi) and nontyphoidal (S. enteritidis and typhimurium). Salmonella | |
---|---|---|
Gram stain Gram stain Klebsiella/structure | Gram-negative bacilli | Gram-negative bacilli |
Lactose fermentation | Non-lactose-fermenting | Non-lactose-fermenting |
Oxidase Oxidase Neisseria | Negative | Negative |
H2S production | No | Yes |
Motility Motility The motor activity of the gastrointestinal tract. Gastrointestinal Motility | No | Yes (with flagella Flagella A whiplike motility appendage present on the surface cells. Prokaryote flagella are composed of a protein called flagellin. Bacteria can have a single flagellum, a tuft at one pole, or multiple flagella covering the entire surface. In eukaryotes, flagella are threadlike protoplasmic extensions used to propel flagellates and sperm. Flagella have the same basic structure as cilia but are longer in proportion to the cell bearing them and present in much smaller numbers. Helicobacter) |
Virulence factors Virulence factors Those components of an organism that determine its capacity to cause disease but are not required for its viability per se. Two classes have been characterized: toxins, biological and surface adhesion molecules that affect the ability of the microorganism to invade and colonize a host. Haemophilus | Endotoxin Endotoxin Toxins closely associated with the living cytoplasm or cell wall of certain microorganisms, which do not readily diffuse into the culture medium, but are released upon lysis of the cells. Proteus, Shiga toxin Shiga toxin A class of toxins that inhibit protein synthesis by blocking the interaction of ribosomal RNA; with peptide elongation factors. They include shiga toxin which is produced by Shigella dysenteriae and a variety of shiga-like toxins that are produced by pathologic strains of Escherichia coli such as Escherichia coli o157. Diarrheagenic E. coli | Endotoxin Endotoxin Toxins closely associated with the living cytoplasm or cell wall of certain microorganisms, which do not readily diffuse into the culture medium, but are released upon lysis of the cells. Proteus, Vi capsular antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination |
Reservoir Reservoir Animate or inanimate sources which normally harbor disease-causing organisms and thus serve as potential sources of disease outbreaks. Reservoirs are distinguished from vectors (disease vectors) and carriers, which are agents of disease transmission rather than continuing sources of potential disease outbreaks. Humans may serve both as disease reservoirs and carriers. Escherichia coli | Humans | Humans (S. typhi), animals Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, animalia was one of the kingdoms. Under the modern three domain model, animalia represents one of the many groups in the domain eukaryota. Cell Types: Eukaryotic versus Prokaryotic |
Dose to produce disease | Small inoculum (acid stable) | Large dose (inactivated by acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance) |
Infection spread | Cell-to-cell (no hematogenous Hematogenous Hepatocellular Carcinoma (HCC) and Liver Metastases spread) | Can spread hematogenously |