Mycobacteria (Tuberculosis, Leprosy, Atypical) MCQs

Microbiology · 79 free questions with answers & explanations.

1. A 35-year-old with AIDS (CD4 count 40 cells/μL) develops fever and generalized lymphadenopathy. Lymph node biopsy shows macrophages loaded with AFB but no granuloma formation. The most likely diagnosis is:
2. A leprosy patient has diffuse skin thickening, loss of eyebrows, and a Bacterial Index of 5+ on slit-skin smear. Lepromin test is negative. His biopsy shows Virchow cells (foam cells). Classification and the type of immunity is:
3. The primary tuberculosis complex in a child consists of a peripheral lung lesion and enlarged hilar lymph nodes. This combination was originally described as:
4. A 30-year-old patient on anti-TB therapy develops tingling and numbness in hands and feet after 2 months. The responsible drug acts by competing with pyridoxine (Vitamin B6). This side effect is most common in:
5. A sputum smear from a suspected TB patient is reported as 3+ AFB positive on Ziehl-Neelsen staining. In Ziehl-Neelsen staining, the primary stain used and the reason for acid-fastness of mycobacteria is:
6. A sputum sample from a suspected TB patient is processed using the Petroff's method (4% NaOH decontamination) before culture. What is the primary purpose of this decontamination step?
7. The phenomenon of 'cording' observed in virulent Mycobacterium tuberculosis colonies is attributed to which specific cell wall component?
8. A healthcare worker exposed to TB converts her tuberculin test from negative to positive. She is placed on isoniazid preventive therapy (IPT). The primary mechanism of isoniazid action is:
9. In leprosy, a borderline tuberculoid (BT) patient upgrades to tuberculoid (TT) type during reaction. This Type 1 (reversal) reaction is characterized by:
10. Mycobacterium avium-intracellulare complex (MAC) causes disseminated disease almost exclusively in patients with CD4+ T-cell counts below:
11. A patient on anti-TB treatment develops peripheral neuropathy. Investigation reveals pyridoxine deficiency induced by a first-line drug. Which mechanism explains why this drug causes pyridoxine deficiency?
12. Mycobacterium tuberculosis survives within macrophage phagosomes by a specific mechanism. The bacterial protein that prevents phagosome acidification and lysosome fusion is:
13. In lepromatous leprosy, despite high bacillary load, the lepromin test is negative. The immunological reason is:
14. Which atypical mycobacterium causes disseminated infection specifically in patients with idiopathic CD4+ lymphocytopenia or those with a genetic defect in the IFN-gamma/IL-12 axis?
15. A 35-year-old patient with smear-positive pulmonary TB is started on first-line treatment. After 2 months, sputum culture remains positive. DST reveals resistance to isoniazid (INH) and rifampicin but sensitivity to fluoroquinolones and injectable agents. Which drug resistance pattern is this?
16. In the immunohistochemistry of leprosy lesions, the Ridley-Jopling classification relies on the bacterial index (BI) and morphological index (MI) of AFB in slit-skin smears. Which form of leprosy has the highest bacterial index (6+) and lowest cell-mediated immunity?
17. A 45-year-old patient with HIV (CD4 = 75 cells/µL) develops fever, weight loss, diarrhoea, and elevated ALP. Blood culture yields acid-fast bacilli growing at 25–37°C on Löwenstein-Jensen medium. The organism forms smooth, nonpigmented colonies and does NOT produce niacin. The most likely organism and treatment are:
18. Rifampicin monoresistance in M. tuberculosis most commonly results from mutation in which specific region of the rpoB gene?
19. Isoniazid (INH) resistance in Mycobacterium tuberculosis most commonly arises from mutation in which gene, and what enzyme activity does INH normally inhibit?
20. In leprosy, the Ridley-Jopling classification defines the lepromatous pole (LL) as immunologically anergic to M. leprae antigens. Which T-cell subset dominance characterizes the lepromatous pole as compared to the tuberculoid pole?
21. A patient with HIV and CD4 count of 30 cells/μL presents with disseminated infection — fever, hepatosplenomegaly, anemia, and positive blood culture. Ziehl-Neelsen staining of buffy coat reveals non-chromogenic AFB forming serpentine cords. Which mycobacterium species is most likely responsible?
22. The Mantoux test uses 5TU of PPD (purified protein derivative) intradermally. In a patient recently vaccinated with BCG, a 12 mm induration is read at 48–72 hours. Which immunological mechanism underpins this reaction?
23. A patient with pulmonary tuberculosis is found to have an M. tuberculosis isolate resistant to both rifampicin and isoniazid on drug susceptibility testing (DST). This qualifies as MDR-TB. The molecular mechanism of rifampicin resistance in M. tuberculosis most commonly involves:
24. In leprosy, the Mitsuda (lepromin) test uses integral lepromin (Dharmendra antigen uses heat-killed lepromin). A positive Mitsuda reaction (late reaction at 3–4 weeks) indicates:
25. A 45-year-old patient with silicosis presents with progressive cavitary pulmonary disease. Sputum culture on Löwenstein-Jensen medium at 37°C grows smooth cream-colored colonies in 3 weeks that are Arylsulfatase-negative, Niacin-negative, and Nitrate-reduction-negative. Pigmentation develops only on exposure to light. The organism is most likely:
26. In the WHO classification of leprosy for treatment purposes, multibacillary (MB) leprosy is defined as having more than five skin lesions and/or positive slit-skin smear. Which regimen constitutes standard MB-MDT (multi-drug therapy) as per current WHO guidelines?
27. A patient with pulmonary tuberculosis develops peripheral neuropathy and sideroblastic anaemia after 2 months of anti-TB treatment. These adverse effects are most likely attributable to which drug and which mechanism?
28. Mycobacterium leprae is the only known pathogen that infects peripheral nerves and Schwann cells. What is the receptor through which M. leprae invades Schwann cells and causes nerve damage?
29. A patient with HIV (CD4 count 35/µL) develops disseminated Mycobacterium avium complex (MAC) infection with fever, weight loss, diarrhoea, and hepatosplenomegaly. Blood cultures confirm MAC. The first-line prophylaxis for MAC in HIV patients with CD4 <50/µL is:
30. The QuantiFERON-TB Gold In-Tube (QFT-GIT) assay measures IFN-γ release in response to M. tuberculosis–specific antigens. Which antigens are used in QFT-GIT that distinguish it from PPD-based tuberculin skin tests and avoid cross-reactions with BCG?
31. A 35-year-old HIV-positive man (CD4 = 80/µL) develops fever, night sweats and extensive lymphadenopathy. Blood cultures grow mycobacteria in the BACTEC system. The organism is non-chromogenic, grows at 37°C, and is resistant to isoniazid and pyrazinamide but sensitive to clarithromycin and ethambutol. Which organism is most likely?
32. A slit-skin smear from a borderline lepromatous (BL) leprosy patient shows a Bacterial Index (BI) of +4. After 6 months of MDT (multibacillary regimen), the patient develops a new painful nodular erythema of the skin with fever and neuritis. The reaction is classified as ENL (Erythema Nodosum Leprosum). Which immunological mechanism underlies ENL?
33. Which mycobacterium is the causative agent of Buruli ulcer, and what is the primary virulence factor responsible for the characteristic extensive skin and soft tissue necrosis with undermined edges?
34. In histopathological examination of a lymph node from a patient with primary TB, the central area of the granuloma shows structureless eosinophilic material. What is the correct term for this necrosis and which cell is characteristically central to the granuloma in TB?
35. A 28-year-old HIV-positive patient (CD4 count 80 cells/µL) has a positive Mantoux test (>5 mm is significant in HIV) but a normal chest X-ray. The recommended preventive therapy under the National TB Elimination Programme (NTEP) India is:
36. The CBNAAT (Xpert MTB/RIF) assay simultaneously detects M. tuberculosis DNA and resistance to rifampicin by probing which gene?
37. In the histopathological classification of leprosy, Virchow cells (lepra cells) are foamy macrophages packed with bacilli seen in which type of leprosy?
38. A 45-year-old immunocompetent patient with a history of hot-tub use develops multiple nodular skin lesions on the arms and trunk. A skin biopsy AFB culture at 30–33°C grows a scotochromogenic, rapidly-growing Mycobacterium. The most likely organism is:
39. A 32-year-old HIV-positive patient (CD4 count 45 cells/μL) presents with fever, night sweats, and cervical lymphadenopathy. Lymph node aspirate shows AFB on ZN stain. Culture on LJ medium at 37°C grows slowly (8 weeks) with smooth, buff-colored colonies. On molecular drug susceptibility testing (GenoType MTBDRplus), no rpoB or katG mutations are detected. This is MOST consistent with:
40. A 28-year-old leprosy patient on MDT (MB regimen) for 8 months develops sudden onset of erythema and tenderness over existing skin lesions, fever, and peripheral nerve thickening. New skin lesions appear. Nerve function assessment shows new sensory loss in the ulnar nerve territory. This reaction pattern is MOST consistent with:
41. GeneXpert MTB/RIF Ultra (Xpert Ultra) has improved sensitivity for TB detection compared to the original Xpert MTB/RIF. Which specific technical modification in Ultra accounts for its higher sensitivity in paucibacillary specimens such as CSF?
42. A patient is diagnosed with pre-XDR TB (extensively drug-resistant TB). According to the WHO 2022 revised definition, pre-XDR TB is defined as TB that is resistant to rifampicin AND:
43. A sputum sample from a suspected TB patient is smear-negative but culture-positive. Line probe assay (LPA) on a subsequent sputum sample detects wild-type rpoB band absence and mutation in codon 531. What does this indicate?
44. A leprosy patient on multidrug therapy (MDT) develops sudden onset painful erythematous skin nodules with fever, malaise, and leukocytosis. Nerve function is not impaired. What is this reaction and its management?
45. A 45-year-old patient with HIV (CD4 = 60) develops fever, night sweats, and markedly elevated alkaline phosphatase. Blood culture in BACTEC MYCO/F Lytic bottle grows slowly at 37°C and on Middlebrook agar shows flat, rough, non-pigmented colonies. ZN stain shows short acid-fast bacilli, negative for pigment. What is the most likely organism?
46. A sputum sample from a suspected TB patient is processed using the NALC-NaOH decontamination method. GeneXpert MTB/RIF (Xpert) is performed and returns: MTB DETECTED; Rifampicin RESISTANCE DETECTED. The next step for comprehensive drug susceptibility testing (DST) is:
47. A leprosy patient is classified as multibacillary by the Ridley-Jopling scale (borderline lepromatous, BI = 4+). After 1 year of WHO-MDT (rifampicin + clofazimine + dapsone), he develops erythema nodosum leprosum (ENL). Which of the following best describes the immunology and management of ENL?
48. An HIV-positive patient (CD4 = 50 cells/µL) is found to have Mycobacterium avium complex (MAC) bacteraemia. Which combination is currently preferred for treatment of disseminated MAC in HIV?
49. A 35-year-old HIV-positive man (CD4 count 80 cells/µL) presents with fever, weight loss, and a positive blood culture growing acid-fast bacilli. The organism grows on Löwenstein-Jensen medium as smooth, cream-coloured colonies at 37°C after 3 weeks and is negative for niacin accumulation and nitrate reduction. It is resistant to isoniazid and rifampicin at standard concentrations. Which organism is most likely?
50. A 28-year-old man presents with hypopigmented anaesthetic patches and thickened peripheral nerves. Slit-skin smear from the ear lobe shows an BI (bacteriological index) of 4+ on the logarithmic scale. Which Ridley-Jopling classification and which therapeutic regimen is most appropriate?
51. The Mantoux test (5 TU PPD intradermally) is performed in a 10-year-old child with BCG vaccination at birth. The induration reads 8 mm at 72 hours. How should this result be interpreted in the Indian context?
52. A 45-year-old man with confirmed pulmonary TB is found to have isoniazid (INH) resistance only on drug susceptibility testing. His sputum smear remains positive at 2 months. According to RNTCP/NTEP 2022 guidelines for HR-TB (isoniazid-resistant TB), what is the standard regimen?
53. A sputum sample sent for AFB culture grows mycobacteria on Lowenstein-Jensen (LJ) medium after 6 weeks as rough, buff-coloured colonies. Line probe assay (LPA) shows a mutation in the rpoB gene (S450L substitution). The most appropriate initial drug regimen is:
54. A patient with leprosy develops sudden painful swelling and redness of multiple existing skin patches along with fever and arthralgia. Nerve tenderness is also noted. The most likely reaction type and immediate management is:
55. A patient on anti-TNF therapy (infliximab) for rheumatoid arthritis is found to have IGRA (interferon-gamma release assay) positive but no active disease on chest X-ray. The preferred drug regimen for latent TB infection (LTBI) in this scenario is:
56. A Runyon group IV mycobacterium is identified in a post-surgical wound. It grows rapidly (within 7 days) on LJ medium, is non-photochromogen, and is resistant to most antibiotics except amikacin and clarithromycin. It is most likely:
57. The Mitsuda reaction (lepromin test — late reaction) is used to assess:
58. A 32-year-old HIV-positive patient (CD4 count 45 cells/µL) has disseminated infection with fever and cervical lymphadenopathy. Blood culture on BACTEC system grows a slow organism. Ziehl-Neelsen stain of lymph node biopsy shows weakly acid-fast rods with a beaded pattern. Colonies on Lowenstein-Jensen medium are non-chromogenic at 37°C. The most likely organism is:
59. A Line Probe Assay (LPA — Hain GenoType MTBDRplus) performed on sputum from a tuberculosis patient detects a probe-hybridization pattern showing absence of the rpoB wild-type band WT8 and presence of MUT3 band. This finding indicates resistance to which drug?
60. A patient from Tamil Nadu presents with a pale hypoesthetic skin lesion with absent sweating and hair fall. Skin slit smear shows 0 AFB per 100 fields; biopsy shows epithelioid cell granulomas with Langhans giant cells and no detectable bacilli. Lepromin test (Mitsuda reaction at 28 days) shows a 10 mm indurated nodule. This patient is classified as:
61. The Xpert MTB/RIF Ultra assay differs from the first-generation Xpert MTB/RIF in which important diagnostic feature?
62. A 35-year-old HIV-positive patient (CD4 count 40 cells/µL) presents with fever, weight loss, and hepatosplenomegaly. Blood culture on BACTEC 13A medium grows acid-fast bacilli after 3 weeks. The isolate grows at 37°C and 42°C but not 25°C, and produces smooth, non-pigmented colonies. It is resistant to isoniazid and susceptible to clarithromycin. Which organism is this?
63. In the Ridley-Jopling classification of leprosy, a patient has 4 skin lesions, poorly defined borders, reduced but not absent sensation, and biopsy shows foamy macrophages with many bacilli and no lymphocytic infiltrate. What type of leprosy is this, and what is the lepromin test result?
64. A patient on a standard anti-TB regimen for 3 months remains sputum smear-positive. Drug susceptibility testing via Line Probe Assay (LPA) shows rpoB gene mutation (D516V) and absence of wild-type band for rpoB. What do these findings indicate?
65. An immunocompetent patient with a history of aquarium fish handling presents with a chronic nodular ulcer on the right hand tracking up the forearm in a sporotrichoid pattern. Biopsy culture grows M. marinum. What is the preferred treatment?
66. A 35-year-old patient with pulmonary tuberculosis fails to respond to Category I DOTS regimen after 5 months. Sputum culture on LJ medium grows M. tuberculosis. Line probe assay (LPA — MTBDRplus) shows absence of wild-type band and presence of mutant band for rpoB codon 531 (Ser531Leu). No inhA or katG mutation detected. What is the drug susceptibility profile of this isolate?
67. A 45-year-old HIV-negative chronic cough patient from Kerala has sputum AFB smear-negative but GenXpert Ultra positive for Mycobacterium tuberculosis complex with RIF 'INDETERMINATE.' Sputum culture grows AFB at 6 weeks. What is the most appropriate next diagnostic step?
68. A patient with borderline tuberculoid (BT) leprosy has a single hypopigmented macule with partial sensory loss. Slit-skin smear (SSS) bacteriological index (BI) is 0. Which immunological test, if performed, would show the strongest delayed-type hypersensitivity reaction?
69. M. avium complex (MAC) infection is the most common opportunistic mycobacterial infection in HIV-positive patients with CD4 counts below a threshold. At what CD4 cell count does NACO and WHO recommend MAC prophylaxis with azithromycin?
70. A patient with HIV and CD4 of 40 cells/µL presents with disseminated infection. Blood cultures on BACTEC grow an organism after 10 days; colonies on LJ medium at 37°C appear as smooth buff-coloured colonies. The organism is pigmented only when grown in the dark. Niacin test is negative and nitrate reduction is negative. This most likely represents:
71. In leprosy, the Mitsuda (lepromin) reaction is read at 4 weeks and represents a granulomatous response to M. leprae antigens. A positive Mitsuda reaction indicates:
72. The recommended treatment for MDR-TB (resistant to at least INH and rifampicin) under current WHO 2022 guidelines uses a 6-month all-oral BPaL regimen. Which drugs compose this regimen?
73. A 60-year-old COPD patient (heavy smoker, no immunosuppression) develops progressive pulmonary disease with upper-lobe fibronodular infiltrates. BAL grows AFB that are acid-fast, rapidly growing (colonies within 7 days on LJ medium), non-chromogenic, and resistant to isoniazid and rifampicin but susceptible to amikacin and clarithromycin. Which organism is most likely?
74. In leprosy, the Ridley-Jopling classification is based on the immune spectrum. A patient has 4 skin lesions with well-defined edges, diminished sensation, negative slit-skin smear (BI = 0), and positive lepromin test. Where does this patient fall on the spectrum, and what WHO treatment regimen applies?
75. A patient on standard first-line TB treatment (HRZE) for 2 months has a persistently positive sputum culture. DST reveals isoniazid resistance (katG mutation) with preserved rifampicin susceptibility. This is classified as:
76. Leprosy reaction Type 1 (reversal reaction) must be distinguished from Type 2 (erythema nodosum leprosum, ENL). Which feature is characteristic of Type 1 reversal reaction?
77. Mycobacterium kansasii causes pulmonary disease resembling TB in immunocompromised patients. Which antibiotic regimen is recommended for M. kansasii pulmonary disease?
78. A sputum culture from a patient with previously treated pulmonary TB grows M. tuberculosis resistant to isoniazid and rifampicin but susceptible to fluoroquinolones and injectable agents (amikacin/kanamycin). This drug resistance pattern defines:
79. The IGRA (interferon-gamma release assay) for latent TB uses M. tuberculosis-specific antigens absent in BCG and most NTM. These antigens are encoded in the 'region of difference 1' (RD1). Which antigens are used in commercial IGRA assays?