Microbiology
Summary
Chlamydia species are obligate intracellular, gram-indeterminate bacteria (they take up Gram stain poorly due to little or no muramic acid (a component of peptidoglycan) in their cell walls). Chlamydia spp. exhibit a unique developmental cycle with elementary bodies being the extracellular, infectious form and reticulate bodies being the intracellular, replicating form. The intracytoplasmic reticulate bodies can be seen as intracellular inclusion bodies on microscopy and can be visualized using Giemsa stain. Nucleic acid amplification tests (NAATs) are the preferred method for detection.
Chlamydia trachomatis serovars D-K and L1-L3 cause sexually transmitted infections (chlamydia) with symptoms such as watery discharge. These STIs may lead to pelvic inflammatory disease or be transmitted from mother to child during delivery, causing conjunctivitis or pneumonia. Chlamydia trachomatis serovars L1-L3 cause lymphogranuloma venereum (LGV) and A-C can lead to trachoma, an eye infection. Reiter's syndrome, characterized by uveitis, urethritis, and arthritis, can develop as a complication. Chlamydophila pneumoniae and Chlamydophila psittaci can cause atypical pneumonia, and macrolides and tetracyclines are effective against Chlamydia spp. For suspected chlamydial infection with Neisseria gonorrhoeae coinfection, ceftriaxone should be administered alongside azithromycin or doxycycline.
Lesson Outline
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FAQs
Giemsa stain is often used in cytological studies to visualize Chlamydia, helping in its initial detection. However, it is not as specific or sensitive as nucleic acid amplification tests (NAATs), which are today's gold standard for detecting Chlamydia infections. NAATs are highly sensitive and specific, making them the preferred method for diagnosing Chlamydia trachomatis, Chlamydophila pneumoniae, and Chlamydophila psittaci.
Chlamydia infections might be asymptomatic or can present with a range of symptoms based on the infecting species. Chlamydia trachomatis, often involved in sexually transmitted infections, can lead to symptoms such as urethritis, cervicitis, and pelvic inflammatory disease. Reactive arthritis can be a complication. On the other hand, Chlamydophila pneumoniae can cause atypical pneumonia, while Chlamydophila psittaci are associated with a systemic illness that may include pneumonia.
Muramic acid is unique to bacterial cell walls and traditionally used to distinguish bacterial from eukaryotic cells. However, the cell wall of Chlamydia species, such as Chlamydia trachomatis, Chlamydophila pneumoniae, and Chlamydophila psittaci, are characterized by the little or no muramic acid, making them resistant to antibiotics like penicillin that target cell walls. This characteristic contributes to difficulties in treating infections caused by these species.
Macrolides, such as azithromycin, and tetracyclines, specifically doxycycline, are commonly used to treat Chlamydia infections. They are effective due to their intracellular penetration and their ability to inhibit protein synthesis in the Chlamydia organism. This disrupts the life cycle of the bacteria and prevents it from surviving and replicating within host cells.
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