Mycobacteria, spirochaetes and atypical bacteria

26 NEET-PG practice questions on Mycobacteria, spirochaetes and atypical bacteria, part of Microbiology. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Medium

   A 40-year-old farm worker from Vellore has had fever and headache for eight days. There is a painless black-crusted eschar in the right axilla with tender axillary nodes. Platelets are 80,000/µL and ALT is 110 U/L; the malaria rapid test is negative. What is the drug of choice?

   1. ACiprofloxacin
   2. BCeftriaxone
   3. CArtesunate
   4. DDoxycycline

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   Answer: D · Doxycycline

   Fever with an eschar, regional lymphadenopathy, thrombocytopenia and raised transaminases in a rural worker is scrub typhus, caused by Orientia tsutsugamushi and transmitted by the larval trombiculid mite (chigger). Doxycycline is the drug of choice; azithromycin is used in pregnancy and young children. Diagnosis is supported by scrub typhus IgM ELISA, but treatment should start on clinical grounds because delay leads to pneumonitis, myocarditis or meningoencephalitis.

   • A: Fluoroquinolones are not reliable for scrub typhus and have been linked to treatment failure.
   • B: Ceftriaxone does not act against Orientia, an obligate intracellular organism.
   • C: Artesunate treats malaria; the eschar and negative malaria test point elsewhere.

2. Question 2 · Medium

   A 40-year-old farmer from Kottayam is admitted on day 12 of an illness with fever, jaundice and oliguria after working in flooded fields. Consider these statements about laboratory diagnosis of leptospirosis: 1. Blood culture gives the best yield in the first week of illness. 2. Leptospires are shed in urine from about the second week. 3. The microscopic agglutination test uses live leptospires. 4. The Weil-Felix test is positive. Which statements are correct?

   1. A2, 3 and 4 only
   2. B1 and 2 only
   3. C1, 2 and 3 only
   4. D2 and 4 only

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   Answer: C · 1, 2 and 3 only

   Statements 1, 2 and 3 are correct. Leptospires circulate in blood (and CSF) in the first, leptospiraemic week, when blood culture in EMJH or Korthof's medium is most useful; antibodies and urinary shedding follow from the second, immune phase. The reference MAT mixes serum with live leptospires of several serovars and is read under dark-field microscopy. The Weil-Felix test uses Proteus antigens and detects rickettsial antibodies, so it has no place in leptospirosis.

   • A: Includes statement 4 and leaves out blood culture in the first week.
   • B: Leaves out statement 3; MAT uses live leptospires.
   • D: Includes the Weil-Felix test and leaves out statements 1 and 3.

3. Question 3 · Medium

   A 34-year-old man with multibacillary leprosy completes 12 months of MDT. His bacteriological index has fallen from 5+ to 4+, and the morphological index is now 0% (earlier 12%). He has no new lesions. How should these smear results be interpreted?

   1. AThe bacilli are dead and are cleared slowly
   2. BDapsone resistance has developed
   3. CThe disease has relapsed during therapy
   4. DMDT should be extended for another twelve months

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   Answer: A · The bacilli are dead and are cleared slowly

   The morphological index (MI) is the percentage of solid, uniformly stained bacilli, which are taken as viable; it falls to zero within months of effective MDT. The bacteriological index (BI) counts all bacilli, living and dead, on a logarithmic scale, and falls slowly, by about one log a year, because dead bacilli are removed slowly by macrophages. A falling BI with an MI of zero therefore shows a good response, and MDT ends at the fixed duration. A rise in BI or the reappearance of solid bacilli would suggest relapse or resistance.

   • B: Resistance would leave solid-staining bacilli, so MI would not fall to zero.
   • C: Relapse shows new lesions and a rising BI, not a falling one.
   • D: MDT is given for a fixed duration; a slowly falling BI is not a reason to extend it.

4. Question 4 · Medium

   Sputum from a 42-year-old man with suspected TB in a Pune hospital is inoculated on Lowenstein-Jensen medium. Which component of the medium suppresses contaminating bacteria?

   1. AMalachite green
   2. BAsparagine
   3. CCoagulated egg
   4. DGlycerol

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   Answer: A · Malachite green

   Lowenstein-Jensen medium is an egg-based medium in which malachite green inhibits most contaminating bacteria that survive decontamination of the sputum. Egg supplies lipids and coagulates on inspissation to give a solid slope. Glycerol and asparagine improve growth of M. tuberculosis. Colonies are rough, buff and tough and take 2-8 weeks to appear, which is why liquid culture and NAAT are used for faster results.

   • B: Asparagine is a nitrogen source that supports growth.
   • C: Egg provides nutrients and solidifies the medium; it has no selective action.
   • D: Glycerol promotes growth of M. tuberculosis; it does not inhibit contaminants.

5. Question 5 · Easy

   A 35-year-old sewage worker in Mumbai is admitted after the monsoon with fever, calf pain, conjunctival suffusion and jaundice. The physician suspects leptospirosis. Which serological test is the reference (gold standard) test for this infection?

   1. AWidal tube agglutination test
   2. BMicroscopic agglutination test
   3. CWeil-Felix agglutination test
   4. DPaul-Bunnell heterophile test

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   Answer: B · Microscopic agglutination test

   The microscopic agglutination test (MAT) is the reference serological test for leptospirosis. Patient serum is mixed with live leptospires of a panel of serovars and agglutination is read under dark-field microscopy; a fourfold rise between paired samples, or a high single titre, supports the diagnosis and suggests the serogroup. Because MAT needs live cultures and expertise, IgM ELISA and rapid IgM tests are used for routine diagnosis. MAT is mainly done in reference laboratories.

   • A: Widal detects antibodies to Salmonella Typhi and Paratyphi.
   • C: Weil-Felix uses Proteus antigens to detect rickettsial antibodies, not leptospiral ones.
   • D: Paul-Bunnell detects heterophile antibodies of infectious mononucleosis.

6. Question 6 · Medium

   A 6-year-old girl from a village near Gorakhpur is admitted in September with acute encephalitis syndrome. Japanese encephalitis IgM in CSF and serum is negative, and malaria tests are negative. No eschar is found. Which test should be sent next to look for a common treatable cause in this region?

   1. AWeil-Felix OX19 titre
   2. BWidal tube test
   3. CDengue NS1 antigen
   4. DScrub typhus IgM ELISA

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7. Question 7 · Easy

   A slit-skin smear is taken from the ear lobe of a 28-year-old man with nodular skin lesions and thickened ulnar nerves. In the Ziehl-Neelsen stain for Mycobacterium leprae, which decolouriser is used?

   1. A1% sulphuric acid
   2. B95% ethyl alcohol
   3. C5% sulphuric acid
   4. D20% sulphuric acid

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8. Question 8 · Medium

   A 48-year-old homeless man in a Kashmir night shelter is admitted in winter with high fever, severe headache and a rash that began on the trunk and spread outwards, sparing the face, palms and soles. He is infested with body lice. Weil-Felix test: OX19 1:640, OX2 1:40, OXK 1:20. What is the most likely cause?

   1. AOrientia tsutsugamushi
   2. BCoxiella burnetii
   3. CRickettsia prowazekii
   4. DRickettsia conorii

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9. Question 9 · Medium

   A 22-year-old woman in a Tamil Nadu village has two hypopigmented, anaesthetic patches on her back and no thickened nerves. A slit-skin smear from one patch shows acid-fast bacilli. How should she be classified and treated under the national programme?

   1. AMultibacillary; 24 months of MB-MDT
   2. BMultibacillary; 12 months of MB-MDT
   3. CPaucibacillary; 6 months of PB-MDT
   4. DPaucibacillary; single-dose rifampicin

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10. Question 10 · Medium

    A 30-year-old labourer in a crowded Bihar hostel has a second bout of high fever, a week after a first bout ended with a crisis of sweating. Several room-mates have body lice. A thick and thin blood smear taken during the fever shows long, loosely coiled spiral organisms between red cells. What is the most likely organism?

    1. ABorrelia recurrentis
    2. BLeptospira interrogans
    3. CPlasmodium vivax
    4. DTreponema pallidum

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11. Question 11 · Hard

    Four weeks after laparoscopic cholecystectomy in a private hospital, a 44-year-old woman has a discharging, non-healing nodule at one port site. Gram stain shows no organisms, but a ZN stain shows acid-fast bacilli. Culture on LJ medium gives non-pigmented colonies within 5 days. Two other patients operated in the same week have similar lesions. What is the most likely cause?

    1. ARapidly growing non-tuberculous mycobacteria
    2. BNocardia asteroides from soil
    3. CMycobacterium leprae from a carrier
    4. DMycobacterium tuberculosis from reactivation

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12. Question 12 · Medium

    A 24-year-old nursing student who received BCG at birth has a tuberculin skin test of 14 mm before starting ward duties. An interferon-gamma release assay (IGRA) on the same day is negative, and she has no symptoms. Why does BCG not make the IGRA positive?

    1. AIGRA measures antibodies rather than T-cell responses
    2. BBCG lacks the ESAT-6 and CFP-10 antigens
    3. CBCG causes T-cell tolerance to PPD
    4. DBCG immunity wanes within one year

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13. Question 13 · Easy

    A 26-year-old man is treated with benzathine penicillin for secondary syphilis at a Suraksha clinic. Which test is used to follow his response to treatment?

    1. AQuantitative TPHA titre
    2. BQuantitative VDRL titre
    3. CFTA-ABS test
    4. DDark-ground microscopy

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14. Question 14 · Medium

    A 38-year-old man with pulmonary TB in Kolkata has a sputum NAAT showing M. tuberculosis with rifampicin resistance not detected. First-line line probe assay shows an inhA promoter mutation, with no katG mutation. What does this result imply?

    1. ALow-level isoniazid resistance, with ethionamide likely to fail
    2. BFluoroquinolone resistance needing a longer regimen
    3. CHigh-level isoniazid resistance, with ethionamide still active
    4. DRifampicin resistance missed by NAAT

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15. Question 15 · Medium

    A 4-year-old boy in a district hospital in Odisha has had fever and weight loss for a month, and his father has sputum-positive TB. He cannot bring up sputum. Which sample is preferred to confirm TB in him?

    1. ASerum for anti-TB IgG antibodies
    2. BNasal swab for Ziehl-Neelsen stain
    3. CBlood culture in an automated liquid system
    4. DEarly morning gastric aspirate for NAAT

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16. Question 16 · Medium

    A 50-year-old man with cough for 3 weeks gives a sputum sample at a designated microscopy centre. On Ziehl-Neelsen staining, the technician counts 6 acid-fast bacilli in 100 oil-immersion fields. How should this smear be reported?

    1. APositive, grade 2+
    2. BScanty, with the count recorded
    3. CNegative for acid-fast bacilli
    4. DPositive, grade 1+

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17. Question 17 · Hard

    A baby is born at 36 weeks in a district hospital to a mother who had no antenatal care. The mother's RPR titre is 1:8 and TPHA is reactive. The baby has hepatosplenomegaly and a desquamating rash on the soles. Which result in the baby best confirms congenital syphilis?

    1. ARPR titre of 1:4 in the baby
    2. BReactive IgG FTA-ABS in the baby
    3. CRPR titre of 1:64 in the baby
    4. DReactive TPHA in the baby

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18. Question 18 · Medium

    A 9-year-old boy from Karnataka who plays with ticks on his pet dog has fever for 8 days and a maculopapular rash on his limbs, palms and soles. Two days later the tips of three fingers turn dusky and cold. What is the basic pathological process behind the finger changes?

    1. ARickettsial infection of endothelial cells causing vasculitis
    2. BCold agglutinins blocking digital capillaries
    3. CImmune complexes deposited in the glomeruli
    4. DToxin-mediated spasm of the digital arteries

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19. Question 19 · Hard

    A 7-year-old girl from a dairy-farming family in Haryana, who drinks unboiled milk, has a painless cervical lymph node mass. The aspirate grows a slowly growing, non-pigmented mycobacterium after 5 weeks. Tests: niacin negative, nitrate reduction negative, growth inhibited by thiophene-2-carboxylic acid hydrazide (TCH), and resistant to pyrazinamide. What is the most likely organism?

    1. AMycobacterium fortuitum
    2. BMycobacterium kansasii
    3. CMycobacterium tuberculosis
    4. DMycobacterium bovis

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20. Question 20 · Medium

    A 24-year-old man attends the STI clinic with a painless, indurated ulcer on the penis that appeared 6 days ago, with firm, non-tender inguinal nodes. VDRL is non-reactive. What is the best investigation now?

    1. ADark-ground microscopy of ulcer exudate
    2. BTzanck smear from the floor of the ulcer
    3. CGram stain of the ulcer base
    4. DRepeat VDRL in the same sample

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21. Question 21 · Hard

    A 23-year-old man has a generalised copper-coloured rash including palms and soles, mucous patches in the mouth and patchy hair loss. The undiluted VDRL is non-reactive, but TPHA is reactive. He had a painless genital ulcer 2 months ago. What should the laboratory do next?

    1. AReport latent syphilis and stop testing
    2. BRepeat VDRL on serially diluted serum
    3. CSend serum for HIV viral load first
    4. DRepeat TPHA on a fresh sample

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22. Question 22 · Easy

    A 30-year-old woman who harvests paddy in Himachal Pradesh has fever for a week and a painless black eschar under her right breast. Scrub typhus IgM ELISA is positive. Which arthropod transmits this infection?

    1. ALarval trombiculid mite
    2. BRat flea
    3. CHuman body louse
    4. DHard tick

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23. Question 23 · Hard

    A 32-year-old man was treated with benzathine penicillin for secondary syphilis 12 months ago. His RPR titre was 1:64 at diagnosis and is now 1:4; TPHA remains reactive. Consider these statements: 1. He has had an adequate serological response. 2. TPHA should turn non-reactive if he is cured. 3. He needs a repeat course of penicillin now. 4. A later rise of RPR to 1:32 would suggest reinfection or relapse. Which statements are correct?

    1. A1, 2 and 4 only
    2. B2 and 3 only
    3. C3 and 4 only
    4. D1 and 4 only

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24. Question 24 · Easy

    A 45-year-old man from Chhattisgarh with lepromatous leprosy agrees to give a skin biopsy for research on M. leprae antigens. The laboratory cannot grow the bacillus on any artificial medium. In which host is M. leprae grown in large numbers for such work?

    1. ALowenstein-Jensen slope
    2. BNine-banded armadillo
    3. CGuinea pig peritoneum
    4. DEmbryonated hen's egg

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25. Question 25 · Medium

    A dermatology postgraduate in Delhi reads lepromin tests in patients across the leprosy spectrum. Consider these statements: 1. The Mitsuda reaction is read 3-4 weeks after injection. 2. The test is strongly positive in lepromatous leprosy. 3. The test indicates prognosis rather than establishing the diagnosis. 4. The Fernandez reaction is read at 48 hours. Which statements are correct?

    1. A1, 2, 3 and 4
    2. B1, 3 and 4 only
    3. C1 and 4 only
    4. D2 and 3 only

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