Sexually Transmitted Infection Microbiology (Syphilis Serology, GC/Chlamydia NAAT) MCQs

Microbiology · 28 free questions with answers & explanations.

1. A 22-year-old woman presents with cervical discharge and dysuria. NAAT (Aptima Combo 2 assay) on a cervical swab tests positive for both Neisseria gonorrhoeae and Chlamydia trachomatis. Culture for N. gonorrhoeae is requested. The selective medium for N. gonorrhoeae culture is:
2. A reactive VDRL titer of 1:64 is found in a 28-year-old man without symptoms. He is confirmed HIV-positive with CD4 count 350 cells/μL. CSF is examined to exclude neurosyphilis. CSF shows: WBC 12 lymphocytes, protein 55 mg/dL, CSF VDRL reactive (1:2). The MOST appropriate treatment is:
3. A male patient presents with urethral discharge; Gram stain shows intracellular gram-negative diplococci within neutrophils. Culture on modified Thayer-Martin medium at 37°C in 5% CO2 grows oxidase-positive, catalase-positive colonies. To confirm Neisseria gonorrhoeae and rule out N. meningitidis, the definitive test is:
4. A woman with a painless indurated ulcer on the vulva has an RPR titre 1:256. TPHA confirms positivity. CSF examination shows 12 lymphocytes/mm³ and CSF VDRL is reactive. She is pregnant at 16 weeks. The diagnosis and treatment are:
5. A 30-year-old woman has VDRL 1:4 reactive, TPHA positive, FTA-ABS positive. She has no history of syphilis treatment. She is 12 weeks pregnant. What is the recommended treatment?
6. A VDRL positive result at 1:16 is found incidentally in a 28-year-old man with no symptoms. TPHA is positive. He claims he completed penicillin treatment for syphilis 6 months ago. What serological response confirms adequate treatment?
7. A 35-year-old man is found to have a positive treponemal test (TPPA positive) on screening but a negative VDRL. He has no history of syphilis treatment. Which scenario best explains this 'reverse algorithm' pattern?
8. For N. gonorrhoeae (GC) detection in a male with urethral discharge and a female with suspected cervical gonorrhoea, NAAT is preferred over culture. What is the primary advantage of NAAT over culture for gonorrhoea diagnosis?
9. A patient is tested for syphilis: VDRL is reactive at 1:64, TPHA is reactive, and FTA-ABS is reactive. After treatment with benzathine penicillin, which serological test best monitors treatment response?
10. NAAT (nucleic acid amplification testing) is the gold standard for diagnosis of chlamydial infections. Chlamydia trachomatis NAAT on first-catch urine has significantly higher sensitivity than culture because:
11. A 26-year-old man has a painless genital ulcer for 2 weeks. VDRL is reactive at 1:32; TPHA is positive. Dark-field microscopy of exudate shows motile corkscrew-shaped organisms with 6–14 regular spiral coils. The drug of choice for early syphilis is:
12. A 22-year-old man presents with painful inguinal lymphadenopathy (buboes) that are fluctuant and mat together. He has a history of a transient painless genital papule 3 weeks ago that has healed. NAAT from inguinal aspirate is positive for Chlamydia trachomatis. Which serovars are responsible for this condition?
13. A 24-year-old woman is found to have a painless indurated genital ulcer. Serology shows RPR reactive 1:8, TPPA positive, IgM anti-Treponema positive. HIV test is negative. She is 10 weeks pregnant. What is the preferred treatment for primary syphilis in pregnancy?
14. A 22-year-old man presents with purulent urethral discharge. Gram stain of the discharge shows Gram-negative intracellular diplococci. The isolate grows on modified Thayer-Martin (MTM) medium. The isolate is found to produce beta-lactamase (PPNG). What is the first-line treatment?
15. A patient with a genital ulcer and inguinal lymphadenopathy has the following serological results: RPR 1:32 (reactive), TPHA positive. 6 months earlier, RPR was 1:16 with TPHA positive after treatment with 2.4 MU benzathine penicillin IM. Current RPR is now 1:32. What does this represent?
16. Neisseria gonorrhoeae is increasingly resistant to standard antibiotics. NACO/WHO currently recommends which first-line treatment for uncomplicated urogenital gonorrhoea given the high rates of fluoroquinolone resistance in India?
17. A 32-year-old man with a painless genital ulcer has the following syphilis serology: VDRL reactive (1:64 titer), TPHA reactive, FTA-ABS reactive. He has no prior syphilis history. The most appropriate management is:
18. In the reverse syphilis screening algorithm (EIA/CLIA first, then VDRL), a specimen tests reactive on treponemal EIA but non-reactive on VDRL. The recommended next step is:
19. NAAT (nucleic acid amplification test) is preferred over culture for detection of Chlamydia trachomatis in urogenital specimens because:
20. Donovanosis (granuloma inguinale) is caused by Klebsiella granulomatis. Its characteristic histological finding and the stain used to demonstrate it are:
21. A 26-year-old man has a painless penile ulcer with indurated edges for 3 weeks. VDRL is reactive at 1:32 dilution. TPHA is also reactive. He denies prior history of syphilis or treatment. What is the interpretation of these results?
22. NAAT (nucleic acid amplification test) for Chlamydia trachomatis on a first-void urine sample from an asymptomatic 22-year-old woman is positive. The specimen was collected into a validated NAAT transport medium. Which of the following is true about chlamydial NAAT?
23. A patient with secondary syphilis (diffuse maculopapular rash including palms and soles, VDRL reactive 1:64) is treated with benzathine penicillin G 2.4 MU IM single dose. When should post-treatment VDRL be repeated to confirm adequate serological response?
24. Gonorrhea caused by Neisseria gonorrhoeae is diagnosed in a 24-year-old male using NAAT on urethral swab. The isolate (on culture) is tested for antibiotic susceptibility. Ceftriaxone MIC is 0.125 µg/mL (resistance breakpoint >0.125 µg/mL per EUCAST). What does this represent?
25. A patient's syphilis serology shows: VDRL reactive 1:32, TPHA reactive. After treatment with benzathine penicillin G 2.4 MU IM, retesting at 6 months shows VDRL 1:4, TPHA reactive. How should this result be interpreted?
26. A patient with syphilis serology shows a 'prozone phenomenon' on VDRL testing. This occurs due to:
27. NAAT for Neisseria gonorrhoeae and Chlamydia trachomatis is the preferred diagnostic method over culture. An important limitation of NAAT for N. gonorrhoeae is:
28. A patient with a painless genital ulcer has negative dark-field microscopy and VDRL is non-reactive on day 5 of the ulcer. The MOST appropriate next diagnostic step is: