Chlamydia

General Characteristics

General characteristics

• Obligate intracellular 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:
  • Cannot produce their own adenosine Adenosine A nucleoside that is composed of adenine and d-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter. Class 5 Antiarrhythmic Drugs triphosphate (ATP)
  • Capable of synthesizing their own macromolecules
• Staining:
  • Visualized using Giemsa stain: nucleic acid stain
  • Classified as gram-negative bacteria gram-negative bacteria Bacteria which lose crystal violet stain but are stained pink when treated by gram’s method. Bacteriology, but exhibit poor Gram staining Gram staining Bacteriology 
  • Cell wall Cell wall The outermost layer of a cell in most plants; bacteria; fungi; and algae. The cell wall is usually a rigid structure that lies external to the cell membrane, and provides a protective barrier against physical or chemical agents. Cell Types: Eukaryotic versus Prokaryotic shows some characteristics of gram-negative bacteria gram-negative bacteria Bacteria which lose crystal violet stain but are stained pink when treated by gram’s method. Bacteriology, but lacks peptidoglycans.
  • Lack of peptidoglycans makes them insensitive to β-lactam antibiotics.
  • Iodine Iodine A nonmetallic element of the halogen group that is represented by the atomic symbol I, atomic number 53, and atomic weight of 126. 90. It is a nutritionally essential element, especially important in thyroid hormone synthesis. In solution, it has anti-infective properties and is used topically. Thyroid Hormones stain: to visualize inclusion bodies (replicating intracellular forms)
• Life cycle:
  • Elementary body (EB): infectious, metabolically inactive, spore-like
  • Reticulate body (RB): non-infectious, metabolically active, replicative form (seen only within host cells)
• Pathogenic species:
  • C. trachomatis 
  • C. psittaci 
  • C. pneumoniae

Mnemonic

To help recall the characteristics of the life cycle, remember the 3 Es and 2 Rs:

• Elementary bodies Enter the cells and are the “Enfectious” form.
• Reticular bodies Replicate.

Reservoirs, transmission, and risk factors

Clinical Relevance (C. trachomatis)

Epidemiology

• Most common bacterial cause of sexually transmitted genital infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease in the United States
• More prevalent in young adults (< 26 years of age)
• Higher incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency in African Americans, Alaskans, and Native Americans
• Co-infection with other sexually transmitted pathogens is common.
• Trachoma Trachoma A chronic infection of the conjunctiva and cornea caused by Chlamydia trachomatis. Chlamydial Infections (ocular infection) is endemic in some areas of Africa, Asia ASIA Spinal Cord Injuries, Latin America, the Middle East, and the Pacific Rim.
• Leading infectious cause of blindness Blindness The inability to see or the loss or absence of perception of visual stimuli. This condition may be the result of eye diseases; optic nerve diseases; optic chiasm diseases; or brain diseases affecting the visual pathways or occipital lobe. Retinopathy of Prematurity worldwide

Transmission

• 1 in 20 sexually active young women aged 14–24 years has chlamydia.
• Many infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease are asymptomatic, especially in women.
• Rates of transmission between symptomatic and asymptomatic individuals are unknown.
• Trachoma Trachoma A chronic infection of the conjunctiva and cornea caused by Chlamydia trachomatis. Chlamydial Infections:
  • Person-to-person through ocular and nasal secretions
  • Eye-seeking flies

Pathogenesis

• Elementary bodies invade the host cell through endocytosis Endocytosis Cellular uptake of extracellular materials within membrane-limited vacuoles or microvesicles. Endosomes play a central role in endocytosis. The Cell: Cell Membrane.
• Inside the cell, they convert to the metabolically active reticulate bodies.
• Reticulate bodies replicate inside the host cell via fission.
• They then reorganize into elementary bodies that are released from the cell.
• Clusters of replicating reticulate bodies are known as inclusion bodies and can be visualized using Giemsa, Pap, or iodine Iodine A nonmetallic element of the halogen group that is represented by the atomic symbol I, atomic number 53, and atomic weight of 126. 90. It is a nutritionally essential element, especially important in thyroid hormone synthesis. In solution, it has anti-infective properties and is used topically. Thyroid Hormones staining.
• There are multiple serovars of C. trachomatis:
  • Serovars A–C: cause trachoma Trachoma A chronic infection of the conjunctiva and cornea caused by Chlamydia trachomatis. Chlamydial Infections
  • Serovars D–K:
    • Most common sexually transmitted infection Sexually Transmitted Infection Sexually transmitted infections (STIs) are infections that spread either by vaginal intercourse, anal sex, or oral sex. Symptoms and signs may include vaginal discharge, penile discharge, dysuria, skin lesions (e.g., warts, ulcers) on or around the genitals, and pelvic pain. Some infections can lead to infertility and chronic debilitating disease. Sexually Transmitted Infections (STIs) in the United States
    • Also associated with neonatal conjunctivitis Conjunctivitis Conjunctivitis is a common inflammation of the bulbar and/or palpebral conjunctiva. It can be classified into infectious (mostly viral) and noninfectious conjunctivitis, which includes allergic causes. Patients commonly present with red eyes, increased tearing, burning, foreign body sensation, and photophobia. Conjunctivitis and 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 (acquired during passage through the birth canal Birth canal Pelvis: Anatomy)
  • Serovars L1–L3:
    • Also sexually transmitted
    • Cause lymphogranuloma venereum Lymphogranuloma venereum Subacute inflammation of the inguinal lymph glands caused by certain immunotypes of Chlamydia trachomatis. It is a sexually transmitted disease in the U.S. But is more widespread in developing countries. It is distinguished from granuloma venereum, which is caused by calymmatobacterium granulomatis. Chlamydial Infections ( LGV LGV Subacute inflammation of the inguinal lymph glands caused by certain immunotypes of Chlamydia trachomatis. It is a sexually transmitted disease in the U.S. But is more widespread in developing countries. It is distinguished from granuloma venereum, which is caused by calymmatobacterium granulomatis. Chlamydial Infections)

Clinical presentation

Sexually transmitted:

• Urogenital infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease (serovars D–K):
  • In women:
    • Often asymptomatic 
    • Cervicitis Cervicitis Inflammation of the uterine cervix. Gonorrhea
    • Urethritis Urethritis Inflammation involving the urethra. Similar to cystitis, clinical symptoms range from vague discomfort to painful urination (dysuria), urethral discharge, or both. Urinary Tract Infections (UTIs)
    • Salpingitis
    • Pelvic inflammatory disease Pelvic inflammatory disease Pelvic inflammatory disease (PID) is defined as a polymicrobial infection of the upper female reproductive system. The disease can affect the uterus, fallopian tubes, ovaries, and adjacent structures. Pelvic inflammatory disease is closely linked with sexually transmitted diseases, most commonly caused by Chlamydia trachomatis, Neisseria gonorrhoeae, and Gardnerella vaginalis. Pelvic Inflammatory Disease ( PID PID Pelvic inflammatory disease (PID) is defined as a polymicrobial infection of the upper female reproductive system. The disease can affect the uterus, fallopian tubes, ovaries, and adjacent structures. Pelvic inflammatory disease is closely linked with sexually transmitted diseases, most commonly caused by Chlamydia trachomatis, Neisseria gonorrhoeae, and gardnerella vaginalis. Pelvic Inflammatory Disease)
    • Symptoms include mucopurulent discharge, dysuria Dysuria Painful urination. It is often associated with infections of the lower urinary tract. Urinary Tract Infections (UTIs), and pyuria Pyuria The presence of white blood cells (leukocytes) in the urine. It is often associated with bacterial infections of the urinary tract. Pyuria without bacteriuria can be caused by tuberculosis, stones, or cancer. Urinary Tract Infections (UTIs)
  • In men:
    • Urethritis Urethritis Inflammation involving the urethra. Similar to cystitis, clinical symptoms range from vague discomfort to painful urination (dysuria), urethral discharge, or both. Urinary Tract Infections (UTIs)
    • Epididymitis Epididymitis Epididymitis and orchitis are characterized by acute inflammation of the epididymis and the testicle, respectively, due to viral or bacterial infections. Patients typically present with gradually worsening testicular pain and scrotal swelling along with systemic symptoms such as fever, depending on severity. Epididymitis and Orchitis
    • Proctitis Proctitis Inflammation of the mucous membrane of the rectum, the distal end of the large intestine. Chronic Granulomatous Disease
• Systemic disease:
  • Usually follows a sexually transmitted infection Sexually Transmitted Infection Sexually transmitted infections (STIs) are infections that spread either by vaginal intercourse, anal sex, or oral sex. Symptoms and signs may include vaginal discharge, penile discharge, dysuria, skin lesions (e.g., warts, ulcers) on or around the genitals, and pelvic pain. Some infections can lead to infertility and chronic debilitating disease. Sexually Transmitted Infections (STIs)
  • Arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis
  • Dermatitis Dermatitis Any inflammation of the skin. Atopic Dermatitis (Eczema)
  • Reactive arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis; reactive arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis triad (RAT):
    • Arthritis Arthritis Acute or chronic inflammation of joints. Osteoarthritis, urethritis Urethritis Inflammation involving the urethra. Similar to cystitis, clinical symptoms range from vague discomfort to painful urination (dysuria), urethral discharge, or both. Urinary Tract Infections (UTIs), and uveitis Uveitis Uveitis is the inflammation of the uvea, the pigmented middle layer of the eye, which comprises the iris, ciliary body, and choroid. The condition is categorized based on the site of disease; anterior uveitis is the most common. Diseases of the Uvea
    • More common in men
• Lymphogranuloma venereum Lymphogranuloma venereum Subacute inflammation of the inguinal lymph glands caused by certain immunotypes of Chlamydia trachomatis. It is a sexually transmitted disease in the U.S. But is more widespread in developing countries. It is distinguished from granuloma venereum, which is caused by calymmatobacterium granulomatis. Chlamydial Infections (serovars L1–L3):
  • Primary infection Primary infection Herpes Simplex Virus 1 and 2: genital ulcer, usually small and painless
  • Secondary infection:
    • Involvement of regional lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy (inguinal, perianal)
    • Presents with severe inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation and scarring Scarring Inflammation

Neonatal infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease (serovars D–K):

• Neonatal conjunctivitis Conjunctivitis Conjunctivitis is a common inflammation of the bulbar and/or palpebral conjunctiva. It can be classified into infectious (mostly viral) and noninfectious conjunctivitis, which includes allergic causes. Patients commonly present with red eyes, increased tearing, burning, foreign body sensation, and photophobia. Conjunctivitis:
  • Occurs 2–30 days following birth
  • Causes eyelid swelling Swelling Inflammation, hyperemia, and purulent discharge Purulent Discharge Dacryocystitis
  • Can lead to conjunctival scarring Scarring Inflammation and corneal vascularization
  • Prevention: routine topical erythromycin Erythromycin A bacteriostatic antibiotic macrolide produced by streptomyces erythreus. Erythromycin a is considered its major active component. In sensitive organisms, it inhibits protein synthesis by binding to 50s ribosomal subunits. This binding process inhibits peptidyl transferase activity and interferes with translocation of amino acids during translation and assembly of proteins. Macrolides and Ketolides after birth
• Infant 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:
  • Occurs 2–3 weeks after birth
  • Causes diffuse interstitial 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 untreated

Trachoma Trachoma A chronic infection of the conjunctiva and cornea caused by Chlamydia trachomatis. Chlamydial Infections (serovars A–C):

• Early-stage ( active trachoma Active Trachoma Chlamydial Infections):
  • Conjunctivitis Conjunctivitis Conjunctivitis is a common inflammation of the bulbar and/or palpebral conjunctiva. It can be classified into infectious (mostly viral) and noninfectious conjunctivitis, which includes allergic causes. Patients commonly present with red eyes, increased tearing, burning, foreign body sensation, and photophobia. Conjunctivitis
  • Redness Redness Inflammation, light sensitivity, mucopurulent discharge
• Late-stage (cicatrical trachoma Trachoma A chronic infection of the conjunctiva and cornea caused by Chlamydia trachomatis. Chlamydial Infections):
  • Conjunctival scarring Scarring Inflammation
  • Repeated infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease lead to eyelid scarring Scarring Inflammation, entropion Entropion The turning inward (inversion) of the edge of the eyelid, with the tarsal cartilage turned inward toward the eyeball. Sjögren Syndrome, and eventually corneal damage and blindness Blindness The inability to see or the loss or absence of perception of visual stimuli. This condition may be the result of eye diseases; optic nerve diseases; optic chiasm diseases; or brain diseases affecting the visual pathways or occipital lobe. Retinopathy of Prematurity.

Identification Identification Defense Mechanisms

• Nucleic acid amplification Nucleic acid amplification Laboratory techniques that involve the in-vitro synthesis of many copies of DNA or RNA from one original template. Septic Arthritis testing (NAAT): gold standard
• Other tests mostly used for research Research Critical and exhaustive investigation or experimentation, having for its aim the discovery of new facts and their correct interpretation, the revision of accepted conclusions, theories, or laws in the light of newly discovered facts, or the practical application of such new or revised conclusions, theories, or laws. Conflict of Interest purposes:
  • Serology Serology The study of serum, especially of antigen-antibody reactions in vitro. Yellow Fever Virus
  • Culture (needs to be grown in tissue culture)
  • Antigen detection Antigen detection Respiratory Syncytial Virus
  • Genetic probe Probe A device placed on the patient’s body to visualize a target Ultrasound (Sonography) methods

Clinical Relevance (C. psittaci and C. pneumoniae)

C. psittaci

• Causes about 1% of community-acquired pneumonia Community-Acquired Pneumonia Pneumonia in Children (psittacosis or “parrot 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”)
• Transmitted from birds, usually by inhalation of dried feces
• Human-to-human transmission is possible.
• Incubation Incubation The amount time between exposure to an infectious agent and becoming symptomatic. Rabies Virus period 5–14 days
• Systemic symptoms (may be more prominent than respiratory):
  • 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, myalgias Myalgias Painful sensation in the muscles. Tick-borne Encephalitis Virus, sweats, rigors Rigors Fever
  • Headache Headache The symptom of pain in the cranial region. It may be an isolated benign occurrence or manifestation of a wide variety of headache disorders. Brain Abscess (may be severe), photophobia Photophobia Abnormal sensitivity to light. This may occur as a manifestation of eye diseases; migraine; subarachnoid hemorrhage; meningitis; and other disorders. Photophobia may also occur in association with depression and other mental disorders. Migraine Headache
• Respiratory symptoms: cough, dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, chest pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways, hemoptysis Hemoptysis Hemoptysis is defined as the expectoration of blood originating in the lower respiratory tract. Hemoptysis is a consequence of another disease process and can be classified as either life threatening or non-life threatening. Hemoptysis can result in significant morbidity and mortality due to both drowning (reduced gas exchange as the lungs fill with blood) and hemorrhagic shock. Hemoptysis
• Complications (renal, neurological, hematological) are uncommon, but may occur.

C. pneumoniae

• Responsible for 1%–20% cases of community-acquired pneumonia Community-Acquired Pneumonia Pneumonia in Children
• Human-to-human transmission through respiratory droplets Droplets Varicella-Zoster Virus/Chickenpox or contact
• Presents with 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, cough, shortness of breath Shortness of breath Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea
• Varies in severity from mild to lethal
• Can cause 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 and upper respiratory symptoms
• Chronic infection may contribute to the pathogenesis of atherosclerosis Atherosclerosis Atherosclerosis is a common form of arterial disease in which lipid deposition forms a plaque in the blood vessel walls. Atherosclerosis is an incurable disease, for which there are clearly defined risk factors that often can be reduced through a change in lifestyle and behavior of the patient. Atherosclerosis (nucleic acid of other 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 and viruses Viruses Minute infectious agents whose genomes are composed of DNA or RNA, but not both. They are characterized by a lack of independent metabolism and the inability to replicate outside living host cells. Virology have also been found in atherosclerotic plaques).