Regarding the developmental cycle of Chlamydia trachomatis, which statement correctly describes its two morphological forms?
- A The reticulate body is the infectious extracellular form and the elementary body divides inside the inclusion
- B Both forms are infectious, but only the elementary body undergoes replication
- C The elementary body is the infectious, metabolically inactive form that converts to the dividing reticulate body within host cell inclusions ✓
- D The elementary body replicates by binary fission in the cytoplasm while the reticulate body remains dormant
Correct answer: C. The elementary body is the infectious, metabolically inactive form that converts to the dividing reticulate body within host cell inclusions
Explanation
Chlamydiae have a unique biphasic cycle. The elementary body (EB) is a small, rigid, spore-like, metabolically inert form specialized for extracellular survival and attachment; it is the infectious particle. After endocytosis it differentiates into the larger, fragile reticulate body (RB), which is metabolically active and multiplies by binary fission within a membrane-bound cytoplasmic inclusion. RBs then condense back into EBs, released by host cell lysis or extrusion. Confusing EB and RB functions is a common examination trap.
Reference: Prescott's Microbiology, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.