Chlamydia trachomatis
One-Sentence Definition
Chlamydia trachomatis is an obligate intracellular Gram-negative bacterium with a biphasic developmental cycle that causes STI syndromes, neonatal infection, and trachoma — diagnosed primarily by nucleic acid amplification, not routine culture.
Taxonomy & Morphology
- Family Chlamydiaceae; related respiratory pathogens: C. pneumoniae, C. psittaci
- No peptidoglycan-rich wall suitable for Gram stain in practice — “atypical”
- Elementary body (EB) — infectious, extracellular; reticulate body (RB) — replicating, intracellular
- Serovars: A–C (trachoma), D–K (urogenital/neonatal), L1–L3 (LGV)
Virulence Highlights
- Type III secretion and inclusion formation inside epithelial cells
- Immune evasion via intracellular niche; chronic inflammation drives scarring (fallopian tube, conjunctiva)
- Antigenic variation of major outer membrane protein (MOMP) among serovars
Clinical Syndromes
- Urethritis, cervicitis, PID, epididymitis; often asymptomatic
- Neonatal conjunctivitis / pneumonia
- Trachoma (leading infectious cause of blindness historically)
- LGV: invasive inguinal/anorectal disease (MSM networks important)
Diagnosis
- NAAT / PCR on urine or swab — first-line (Isothermal Nucleic Acid Amplification / syndromic STI panels often include it)
- Culture rarely used clinically; serology limited (except some LGV contexts)
- Test-of-cure selectively (pregnancy, persistent symptoms)
Treatment Notes (conceptual)
- Doxycycline preferred for many urogenital infections; azithromycin alternatives in selected settings
- Treat partners; screen high-risk populations
- LGV needs longer courses — distinguish from non-LGV serovars when invasive
AMR
- Clinical failure more often reinfection/adherence than high-level chromosomal AMR
- Rising macrolide/tetracycline concern in some regions — surveillance evolving
- Not an ESKAPE organism; stewardship still matters for empiric STI regimens
Genomics & Computational Notes
- Small genome (~1 Mb); metabolic dependence on host
- Serovar/genotype from ompA or WGS for LGV outbreak work
- Links: Metagenomics less used than targeted NAAT for routine care
Related Notes
- Neisseria gonorrhoeae (coinfection common) · Genitourinary Infections · Vaccination (no routine human vaccine yet)
- MOCs: MOC - Bacteriology · MOC - Clinical Microbiology · MOC - Diagnostic & Lab Methods
Active Recall
- EB vs RB — which is infectious extracellularly?
- Why is Gram stain useless for diagnosing chlamydial urethritis?
- Which serovar group causes LGV?