Lecture 6: Chlamydia (Obligate Intracellular Parasites)

Question 1

What are the key features of Chlamydia spp.?

Answer 1

Obligate intracellular Gram-negative bacteria, biphasic life cycle (EB/RB), lack peptidoglycan, energy parasites (depend on host ATP).

Question 2

Compare Elementary Bodies (EBs) and Reticulate Bodies (RBs).

Answer 2

EBs: Infectious, metabolically inactive, small, dense.

RBs: Non-infectious, metabolically active, replicate within host inclusions.

Question 3

Name 3 virulence factors of C. trachomatis.

Answer 3

MOMP (Major Outer Membrane Protein): Porin, antigenic variation (VS1-4).

LOS (Lipo-oligosaccharide): Weak endotoxin, triggers inflammation.

Inc Proteins: Prevent lysosome fusion, inhibit apoptosis.

Question 4

Match serovars to diseases:

Answer 4

A-C: Trachoma (chronic eye infection).

D-K: Genital infections (urethritis, PID, infertility).

L1-L3: Lymphogranuloma venereum (LGV; systemic, buboes).

Question 5

How does C. trachomatis cause pelvic inflammatory disease (PID)?

Answer 5

Ascending infection → endometritis/salpingitis → fibrosis/tubal blockage → infertility/ectopic pregnancy.

Question 6

How does Chlamydia evade host immunity?

Answer 6

Intracellular growth (hides from antibodies).

Downregulates MHC I (evades CD8+ T cells).

Inhibits phagolysosome fusion.

Question 7

What is the gold standard for diagnosing C. trachomatis?

Answer 7

NAATs (PCR) – detects bacterial DNA (high sensitivity/specificity). Culture is specific but insensitive.

Question 8

What antibiotics treat C. trachomatis?

Answer 8

Uncomplicated: Azithromycin (single dose) or doxycycline (7-day course).

PID: IV cefoxitin + doxycycline.

Question 9

Why is C. trachomatis highly prevalent?

Answer 9

Asymptomatic in ~70% of women/50% of men → silent transmission. Peak in teens/20s.

Question 10

Why is there no effective Chlamydia vaccine?

Answer 10

Short-lived antibody response (MOMP variation), intracellular niche, poor T-cell memory.