Rickettsia, Chlamydia, Mycoplasma, Spirochetes MCQs

Microbiology · 70 free questions with answers & explanations.

1. A 22-year-old college student presents with gradual onset fever, dry cough, and bilateral lower lobe infiltrates on chest X-ray disproportionate to his mild clinical condition. Cold agglutinin titer is elevated. The causative organism lacks a cell wall and cannot be Gram-stained. The drug of choice is:
2. A 35-year-old male presents with a painless genital ulcer followed by unilateral inguinal lymphadenopathy. Examination reveals enlarged lymph nodes above and below the inguinal ligament with a groove between them (groove sign). The causative organism is:
3. Chlamydia trachomatis has a unique biphasic life cycle. The elementary body (EB) and reticulate body (RB) differ in that the EB:
4. Weil-Felix test is a heterophile agglutination test used in rickettsial disease diagnosis. The test relies on cross-reactive antigens between Rickettsia species and certain Proteus OX strains. However, the test is NEGATIVE in which rickettsial disease?
5. Treponema pallidum cannot be cultivated in routine laboratory media. The cardinal laboratory confirmation of primary syphilis (chancre stage) is therefore best achieved by:
6. Mycoplasma pneumoniae causes atypical pneumonia and, on rare occasions, cold agglutinin-mediated hemolytic anemia. The cold agglutinins in M. pneumoniae infection are directed against which red blood cell antigen?
7. Treponema pallidum is not culturable in standard laboratory media. The serological diagnosis of syphilis uses two types of antibodies. The antigen used in the non-treponemal tests (VDRL/RPR) is:
8. Chlamydia trachomatis causes trachoma (serotypes A-C) and genital infections (D-K). The specific virulence mechanism by which C. trachomatis avoids phagolysosome fusion after entering epithelial cells is:
9. Weil-Felix reaction uses OX-2, OX-19, and OX-K Proteus antigens for serodiagnosis of rickettsial infections. The agglutination of OX-K strains but not OX-2 or OX-19 suggests infection with:
10. Borrelia burgdorferi, the agent of Lyme disease, causes arthritis partly through molecular mimicry. The outer surface protein that cross-reacts with LFA-1 on joint synoviocytes, contributing to autoimmune arthritis, is:
11. Scrub typhus (Orientia tsutsugamushi) is endemic in India. The characteristic eschar at the bite site results from which pathological process, and what is the confirmatory serological test?
12. Chlamydia trachomatis serovars L1, L2, L3 cause Lymphogranuloma Venereum (LGV). Which of the following best characterises the pathogenesis that distinguishes LGV from non-LGV chlamydia urogenital infections?
13. A 40-year-old woman who returned from rural Rajasthan develops high fever, headache, and rash 7 days after a tick bite. IgM ELISA for Rickettsia conorii is positive. Which pathophysiological mechanism accounts for the characteristic maculopapular rash and systemic manifestations of Rickettsia?
14. In tertiary neurosyphilis, the Treponema pallidum Particle Agglutination (TPPA) test is positive but VDRL is negative. This serological pattern is known as:
15. Treponema pallidum cannot be cultured in routine laboratory media. Which serological test combination is recommended for definitive diagnosis of syphilis, distinguishing biological false positives from true syphilis?
16. Chlamydia trachomatis serovars L1, L2, L3 cause lymphogranuloma venereum (LGV). What is the pathognomonic inguinal finding and the preferred diagnostic laboratory method for LGV?
17. Mycoplasma pneumoniae causes atypical pneumonia. A specific serology test uses the patient's serum to agglutinate human group O erythrocytes at 4°C. What are these antibodies called and what antigen do they recognize?
18. Weil's disease (icterohaemorrhagiae leptospirosis) is diagnosed by the microscopic agglutination test (MAT). What is the mechanism of renal injury in severe leptospirosis?
19. Treponema pallidum causes syphilis. The FTA-ABS (fluorescent treponemal antibody absorbed) test detects antibodies against treponemal-specific antigens. Which statement about FTA-ABS is most accurate?
20. Chlamydia trachomatis has a unique biphasic life cycle. After uptake by mucosal epithelial cells, the infectious elementary body (EB) undergoes transformation to the reticulate body (RB) and replication. Which mechanism allows EBs to evade lysosomal fusion upon entry?
21. Borrelia recurrentis causes louse-borne relapsing fever. The recurrent febrile episodes are due to which immunological mechanism?
22. Mycoplasma pneumoniae causes atypical pneumonia. The Weil-Felix test uses which cross-reactive antigen and is positive in which conditions, but NOT in Mycoplasma infection?
23. A 30-year-old man from Andhra Pradesh presents with fever for 10 days, headache, generalised rash that started on the trunk and spread to limbs, and a necrotic eschar on the right groin with regional lymphadenopathy. Weil-Felix test shows agglutination with OX2 antigen. The causative organism is:
24. Chlamydia trachomatis causes trachoma (serovars A–C) and sexually transmitted disease (serovars D–K). Lymphogranuloma venereum (LGV) is caused by serovars L1, L2, L3. LGV classically differs from other urogenital Chlamydia infections by:
25. A 22-year-old man presents with urethral discharge and dysuria. Urethral swab culture on Eaton's agar (PPLO agar) grows tiny 'fried egg' colonies after 10 days. Gram stain shows no organisms. This pattern is consistent with infection by:
26. A 35-year-old rice-field worker from Tamil Nadu develops fever, jaundice, haematuria, and acute kidney injury. Serum creatinine is 5.2 mg/dL. Blood culture in EMJH medium is positive. Microscopic agglutination test (MAT) titre is ≥1:400 against Leptospira interrogans. The pathological mechanism of acute tubular injury in leptospirosis involves:
27. A 30-year-old man from Himachal Pradesh develops acute febrile illness, severe headache, rash starting from wrists/ankles spreading centripetally with petechiae, confusion and thrombocytopenia after a tick bite. Which Rickettsia species is responsible, and what is the specific laboratory test to confirm the diagnosis?
28. Chlamydia trachomatis serovars L1, L2, L3 cause lymphogranuloma venereum (LGV). Which diagnostic test is most specific for confirming active LGV and distinguishing it from other serovars of C. trachomatis?
29. A 28-year-old pregnant woman at 36 weeks develops painless jaundice, haematuria, thrombocytopenia and altered sensorium after exposure to flood water. Weil-Felix test is negative. Microscopic agglutination test (MAT) shows titre ≥1:200 against Leptospira icterohaemorrhagiae. Which organ failure pattern is most characteristic of Weil's disease and what is the first-line antibiotic?
30. A community of pneumonia cases occur in college students with atypical features: gradual onset, dry cough, minimal systemic toxicity, patchy interstitial infiltrates, cold agglutinins positive and failure to respond to beta-lactam antibiotics. Culture of Mycoplasma pneumoniae requires special media. Which component is absent from its cell structure that (a) explains antibiotic resistance to beta-lactams and (b) explains its inability to grow on standard media?
31. A 35-year-old man with a history of unprotected sexual contact 4 weeks ago presents with a painless genital ulcer. VDRL is reactive at 1:8 dilution. TPHA (Treponema pallidum haemagglutination assay) is also reactive. FTA-ABS is reactive. How should these results be interpreted and what is the significance of the TPHA remaining reactive lifelong?
32. A sexually active woman presents with mucopurulent cervical discharge and pelvic pain. NAAT (nucleic acid amplification test) of an endocervical swab is positive for Chlamydia trachomatis. Serovars responsible for genital tract infections and reactive arthritis (formerly Reiter's syndrome) are:
33. A patient with walking pneumonia (atypical pneumonia) has a positive cold agglutinin test at a titre of 1:256. Cold agglutinins in Mycoplasma pneumoniae pneumonia are IgM antibodies directed against which antigen?
34. In secondary syphilis, a patient presents with generalised maculopapular rash including palms and soles. The definitive confirmatory test (not screening) for syphilis is:
35. Leptospirosis diagnosis: In the first week of illness (leptospiraemic phase), the most reliable laboratory method to isolate the organism is:
36. A 25-year-old farmer from Rajasthan presents with fever, headache, eschar (tache noire) over the ankle, and a maculopapular rash that starts on the trunk and spreads peripherally. Weil-Felix test: OX-2 titer 1:320, OX-19 positive, OX-K negative. The MOST likely diagnosis is:
37. Mycoplasma pneumoniae infection in a 20-year-old college student is confirmed by cold agglutinin test (titer 1:128). Cold agglutinins in M. pneumoniae infection are directed against:
38. A 30-year-old sex worker presents with a painless ulcer on the penis (chancre) for 10 days. VDRL test is non-reactive. FTA-ABS (fluorescent treponemal antibody absorption) test is reactive. The interpretation of this discordance is MOST likely:
39. Leptospirosis diagnosis in the first week of illness (leptospiremic phase) is BEST confirmed by:
40. A 28-year-old paddy field worker in Tamil Nadu presents with fever, eschar on the leg, maculopapular rash, and lymphadenopathy. Weil-Felix reaction: OXK positive, OX2 and OX19 negative. The most likely organism is:
41. A 22-year-old male presents with urethral discharge. Gram stain shows no organisms. NAAT (Nucleic acid amplification test) on urethral swab is positive for Chlamydia trachomatis. The serovar responsible, and why culture is not the first-line diagnostic, are:
42. A patient with Lyme disease presents with migratory polyarthritis 4 months after the initial skin rash. Serology shows positive ELISA confirmed by Western blot (IgG bands to OspC and p41). First-line treatment for Lyme arthritis is:
43. A 35-year-old with atypical pneumonia shows 'walking pneumonia' pattern — lobar opacity on X-ray but ambulant patient. Cold agglutinin titre is 1:512. Sputum Gram stain is unremarkable. The causative organism lacks a cell wall, making it resistant to:
44. A patient with secondary syphilis (maculopapular rash including palms and soles, painless mucosal patches) has a positive RPR titre 1:64. A confirmatory test is performed. Which statement about FTA-ABS is correct?
45. A 30-year-old software engineer from Himachal Pradesh presents with fever for 10 days, eschar on the right ankle, generalised maculopapular rash, and severe headache. Weil-Felix test shows OX-K agglutinin titre 1:320, OX-2 negative, OX-19 negative. PCR for Orientia tsutsugamushi is positive. Regarding treatment, which is TRUE?
46. A 25-year-old sexually active man presents with urethral discharge. Gram stain of discharge shows only polymorphs but no gram-negative diplococci. NAAT (nucleic acid amplification test) is positive for Chlamydia trachomatis. Regarding the biology of C. trachomatis, which statement is CORRECT?
47. A 35-year-old patient with secondary syphilis (maculopapular rash on palms and soles, mucous patches) has VDRL positive at 1:32, TPHA positive. He is allergic to penicillin. What is the appropriate alternative treatment?
48. A 25-year-old man from rural Assam presents with fever for 10 days, an eschar on the axilla, and generalised macular rash. Weil-Felix reaction is OXK positive (titre 1:320), OX2 and OX19 negative. What is the most likely diagnosis and first-line treatment?
49. A 22-year-old man presents with painless urethral discharge. NAAT on urethral swab is positive for Chlamydia trachomatis. He is treated with a single dose of azithromycin 1 g. Six months later he returns with rectal bleeding and inguinal lymphadenopathy with grooves (groove sign/sign of the groove). Which Chlamydia trachomatis serovars are responsible for lymphogranuloma venereum (LGV)?
50. A 45-year-old man presents with fever, jaundice, myalgia, and haematuria 2 weeks after wading in floodwaters in Kerala. Leptospira-specific IgM ELISA is positive (titre 1:200). Blood urea is 80 mg/dL and bilirubin is 12 mg/dL. What complication and clinical syndrome does this represent?
51. A 28-year-old woman presents with a painless indurated ulcer (chancre) on the labium majorum that spontaneously resolves. Eight weeks later she develops a generalised maculopapular rash involving palms and soles, generalised lymphadenopathy, and condylomata lata. VDRL titre is 1:64. Which treponemal test is most appropriate to confirm the diagnosis and is non-reactive in false-positive VDRL?
52. A patient from Andhra Pradesh presents with acute febrile illness, eschar (tache noire) at the site of tick bite, and rash. IgM serology for Rickettsia is positive. Weil-Felix reaction shows agglutination of OX-2 proteus strain but not OX-19 or OX-K. The most likely organism is:
53. Mycoplasma pneumoniae causes community-acquired pneumonia (CAP) particularly in younger adults. The hallmark cold agglutinin test becomes positive because M. pneumoniae infection induces antibodies that also agglutinate human O-group red blood cells at 4°C. These antibodies are:
54. A pregnant woman in her first trimester is found to have a reactive VDRL (1:16) and a reactive TPHA (TPPA). She has no symptoms. The most appropriate management is:
55. A 35-year-old from Himachal Pradesh presents with sudden-onset fever, severe headache, and an eschar (tache noire) on the ankle with regional lymphadenopathy. Serology by Weil-Felix test shows agglutination with OX2 proteus antigen but not OX19 or OXK. The most likely diagnosis is:
56. A 24-year-old woman has mucopurulent cervicitis. NAAT (nucleic acid amplification test) from cervical swab is positive for Chlamydia trachomatis. She is not allergic to any antibiotics. The recommended first-line treatment per Indian STI guidelines is:
57. A patient with early secondary syphilis has a positive VDRL at 1:128 and a positive TPPA. After treatment with benzathine penicillin 2.4 MU IM, VDRL is repeated at 6 months and shows 1:16. How should this serological response be interpreted?
58. A 25-year-old man presents with fever, rash starting on wrists and ankles then spreading to trunk, and history of tick bite. Weil-Felix test shows OX-19 and OX-2 agglutination but not OX-K agglutination. Specific serology (IFA) confirms Rickettsia rickettsii. What is the treatment of choice?
59. A 30-year-old man has urethral discharge. Gram stain shows no intracellular diplococci (NGNUD). NAAT on urethral swab is positive for Chlamydia trachomatis. Which serovars of C. trachomatis cause non-gonococcal urethritis?
60. A 28-year-old woman presents with secondary syphilis — diffuse maculopapular rash involving palms and soles. RPR titre is 1:64. Which further test must be performed to confirm the diagnosis?
61. A patient from a forested area of Himachal Pradesh presents with fever, eschar at site of scrub tick attachment, headache and rash. IgM by ELISA for Orientia tsutsugamushi returns positive. Which antibiotic is the drug of choice and why?
62. A sexually active 24-year-old man presents with urethral discharge. Gram stain shows no diplococci. Nucleic acid amplification test (NAAT) from first-void urine is positive for Chlamydia trachomatis but negative for Neisseria gonorrhoeae. What is the recommended treatment per current WHO/NACO STI guidelines?
63. Borrelia burgdorferi infection (Lyme disease) has a characteristic three-stage clinical progression. The earliest and most pathognomonic skin manifestation in stage 1 is:
64. Mycoplasma pneumoniae atypical pneumonia is associated with a specific cold agglutinin. These cold agglutinins are IgM antibodies directed against:
65. Chlamydia trachomatis serovars L1, L2, and L3 cause lymphogranuloma venereum (LGV). The diagnostic test of choice in a patient with painful inguinal lymphadenopathy following unprotected sexual contact is:
66. A 30-year-old male presents with urethral discharge and dysuria for 5 days. NAAT on urethral swab is positive for Chlamydia trachomatis serovars D–K. Three weeks later he develops sterile arthritis, conjunctivitis, and oral ulcers. What is this clinical triad called, and which is the MOST common causative organism in the current era?
67. Mycoplasma pneumoniae causes atypical pneumonia. Which of the following laboratory findings is a DIRECT consequence of M. pneumoniae infection and helps distinguish it from bacterial pneumonia?
68. Mycoplasma pneumoniae causes atypical pneumonia. A key diagnostic feature that differentiates it from typical bacterial pneumonia is:
69. Lyme disease is caused by Borrelia burgdorferi (sensu lato). The two-tier serological testing algorithm used for diagnosis consists of:
70. Chlamydia trachomatis serovars L1, L2, and L3 cause lymphogranuloma venereum (LGV). The diagnostic confirmatory test distinguishing LGV from other C. trachomatis genital infections is: