Bacterial genetics, zoonoses and miscellaneous bacteria

26 NEET-PG practice questions on Bacterial genetics, zoonoses and miscellaneous 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

   Why is a patient's Staphylococcus aureus isolate resistant to cloxacillin and to all other penicillins and cephalosporins except the anti-MRSA agents?

   1. AMethylation of the ribosomal target site
   2. BProduction of an extended-spectrum beta-lactamase enzyme
   3. CAn altered penicillin-binding protein with low beta-lactam affinity
   4. DEfflux pumps that expel the drug from the cytoplasm

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   Answer: C · An altered penicillin-binding protein with low beta-lactam affinity

   Methicillin resistance in staphylococci results from an acquired gene coding an additional penicillin-binding protein with low affinity for beta-lactams, so cell-wall synthesis continues despite the drug; this confers class-wide resistance, which is why vancomycin, linezolid or daptomycin is needed. Key point: MRSA resistance is an altered low-affinity penicillin-binding protein, giving class-wide beta-lactam resistance.

   • A: Ribosomal methylation causes macrolide resistance.
   • B: Extended-spectrum beta-lactamases are a gram-negative mechanism and would not explain this pattern.
   • D: Efflux contributes to some resistances but is not the basis of methicillin resistance.

2. Question 2 · Medium

   Which mechanism of bacterial gene transfer is mediated by a bacteriophage?

   1. AConjugation
   2. BSpontaneous point mutation
   3. CTransduction
   4. DTransformation

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   Answer: C · Transduction

   Transduction is the transfer of bacterial DNA from one cell to another inside a phage particle; transformation is uptake of free DNA from the surroundings, and conjugation needs cell-to-cell contact with a transfer apparatus. Several toxin and resistance genes are carried on phages in nature. Key point: Transduction is phage-mediated transfer; transformation uses free DNA, conjugation needs contact.

   • A: Conjugation requires direct contact between bacteria.
   • B: Mutation alters existing DNA rather than transferring it.
   • D: Transformation involves naked DNA taken up from the environment.

3. Question 3 · Medium

   Statements about antimicrobial resistance: 1. Resistance genes may be transferred between species. 2. Antibiotic use selects for resistant populations. 3. Resistance arises only by chromosomal mutation. 4. Stopping an antibiotic always restores full susceptibility in a ward. Which combination is correct?

   1. A2 and 4 only
   2. B3 and 4 only
   3. C1 and 2 only
   4. D1, 2 and 3 only

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   Answer: C · 1 and 2 only

   Resistance arises both by mutation and by acquisition of genes from other bacteria, and antibiotic exposure selects the resistant subpopulation that then predominates. Because resistance determinants persist on mobile elements and in colonised patients, withdrawing one drug does not promptly restore susceptibility across a unit. Key point: Resistance spreads by gene transfer as well as mutation, and does not reverse quickly when a drug is stopped.

   • A: Statement 4 is wrong while statement 1 is correct but omitted.
   • B: Statements 3 and 4 are both wrong.
   • D: Statement 3 is wrong: horizontal gene transfer is a major route.

4. Question 4 · Hard

   In a 20-bedded intensive care unit with no single rooms, six patients over three weeks are found to carry a carbapenem-resistant Klebsiella with the same resistance gene, although only two have clinical infection. Hand hygiene compliance is audited at 45%, three ventilators are shared between bays, and one nurse covers four beds at night. Two of the six are ventilated, environmental swabs from a shared procedure trolley have grown the same organism, and the unit has one sink for twelve beds. Which package of measures is most likely to end the outbreak?

   1. AClosing the unit for one day for fumigation and reopening it
   2. BCohorting carriers with dedicated staff, hand hygiene and enhanced cleaning
   3. CSwitching the whole unit's empirical therapy to a carbapenem
   4. DA course of colistin for all six patients to clear the organism

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   Answer: B · Cohorting carriers with dedicated staff, hand hygiene and enhanced cleaning

   Transmission is being driven by hands and shared equipment, and most of the reservoir is colonised rather than infected, so the effective response is cohorting carriers with dedicated nurses and devices, improving hand hygiene with audit and feedback, enhanced cleaning, admission screening and stewardship. Treating colonisation does not clear it. Key point: Carbapenem-resistant outbreaks end through cohorting, hand hygiene and cleaning, not by treating carriers.

   • A: A single fumigation day without changing practice is followed by recurrence.
   • C: More carbapenem use would select further resistance.
   • D: Antibiotics do not reliably clear colonisation and add toxicity and selection pressure.

5. Question 5 · Medium

   A hospital's microbiology unit reports that the same plasmid-borne resistance gene has appeared in Klebsiella, Escherichia coli and Enterobacter isolates from one intensive care unit within two months, and typing shows an identical plasmid profile. Which process best explains this pattern?

   1. AConjugative transfer of the plasmid between species
   2. BSpore formation by these gram-negative bacteria
   3. CIndependent spontaneous mutation arising in each of the three species
   4. DLoss of the bacterial chromosome in all three species

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   Answer: A · Conjugative transfer of the plasmid between species

   Conjugation transfers plasmids through direct cell-to-cell contact and crosses species boundaries, so one successful plasmid can carry the same resistance determinant into several genera within a unit. Identical gene and plasmid patterns in different species therefore point to plasmid spread rather than repeated independent mutation. Key point: The same plasmid-borne resistance gene in several species means conjugative plasmid spread.

   • B: Enterobacteriaceae do not form spores.
   • C: Identical mutations arising separately in three species within weeks is highly improbable.
   • D: Bacteria cannot lose the chromosome and survive.

6. Question 6 · Medium

   During a leptospirosis outbreak after floods, the district health officer must advise men clearing debris from waterlogged streets for the next three weeks. Which single preventive package is most appropriate?

   1. ADaily blood counts for a month for each worker
   2. BProtective footwear with doxycycline for high-risk exposure
   3. CChlorination of the standing floodwater in the streets
   4. DTyphoid vaccination of all the workers before deployment

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7. Question 7 · Medium

   A confirmed case of cutaneous anthrax in a village is reported to the district health office, and three cattle died there in the preceding fortnight. Which is the most appropriate public-health response?

   1. AMass vaccination of all villagers with human anthrax vaccine
   2. BClosure of the village school and anganwadi for one month
   3. CBlood cultures from every villager, whether symptomatic or not
   4. DTrace the animal source and ensure safe carcass disposal

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8. Question 8 · Hard

   Which observation would best support the conclusion that a ward's rise in resistant organisms is due to patient-to-patient transmission rather than to antibiotic selection pressure alone?

   1. AIsolates from several patients share an identical typing profile
   2. BResistance rates are rising nationally in surveillance reports too
   3. CEach affected patient had received a different antibiotic class
   4. DTotal antibiotic consumption on the ward has risen over the same period

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9. Question 9 · Medium

   Statements about brucellosis: 1. Transmission follows contact with infected animals or their products. 2. Relapse after treatment is recognised. 3. Single-drug therapy for one week is adequate. 4. Spondylitis is a recognised complication. Which combination is correct?

   1. A1 and 3 only
   2. B2, 3 and 4 only
   3. C1, 3 and 4 only
   4. D1, 2 and 4 only

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10. Question 10 · Hard

    A man treated with doxycycline for presumed scrub typhus is still febrile on day four of treatment, with worsening thrombocytopenia, a rising creatinine and new basal crepitations. Serum taken on day two of illness was negative for scrub typhus IgM, and he lives in a flood-affected block. His oxygen saturation is 93% on room air and the urine shows no casts. What is the most appropriate next step?

    1. ADeclare doxycycline resistance and stop the drug altogether
    2. BManage him as dengue shock syndrome without further testing
    3. CContinue the same treatment unchanged for two further weeks
    4. DReconsider the diagnosis and repeat testing with supportive care

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11. Question 11 · Easy

    A veterinarian in Rajasthan has three months of fever with drenching night sweats, low backache and tenderness over both sacroiliac joints. He has been handling aborted goat material with bare hands, and his serum agglutination titre is strongly positive. Which is the treatment of choice?

    1. ACiprofloxacin for five days
    2. BAmoxicillin for seven days
    3. CAzithromycin for three days
    4. DDoxycycline with rifampicin for six weeks

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12. Question 12 · Medium

    A woman who drinks unpasteurised milk from her own buffaloes has had three months of fever, weight loss and sweats, and now has a new early diastolic murmur with splenomegaly and microscopic haematuria. Three sets of blood cultures taken before antibiotics are reported negative at five days, and the echocardiogram shows aortic valve vegetations. Which diagnosis must be actively excluded, and how?

    1. AViral myocarditis, by serial troponin estimation alone
    2. BNothing further: negative cultures have excluded endocarditis
    3. CBrucella endocarditis, by serology with prolonged culture
    4. DRheumatic carditis, by a throat swab and antistreptolysin titre

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13. Question 13 · Medium

    Under integrated disease surveillance, which event in animals should prompt immediate notification to human health authorities in a rural block?

    1. ASudden unexplained cattle deaths or a rodent die-off
    2. BThe annual shearing of sheep before the summer months
    3. CA seasonal reduction in milk yield among village cattle
    4. DRoutine deworming of livestock by the veterinary officer

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14. Question 14 · Easy

    Which clinical form of plague most requires respiratory precautions because of person-to-person spread?

    1. ACutaneous plague
    2. BPneumonic plague
    3. CBubonic plague
    4. DAsymptomatic pharyngeal carriage

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15. Question 15 · Medium

    Which feature best distinguishes the cutaneous lesion of anthrax from a staphylococcal boil at the bedside?

    1. ASevere tenderness with surrounding spreading cellulitis
    2. BRapid fluctuation developing within about two days
    3. CA central punctum discharging thick yellow pus
    4. DPainlessness with a black eschar and marked oedema

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16. Question 16 · Easy

    Which measure most directly limits the spread of resistance genes within a hospital ward?

    1. ARotating patient bed numbers each week
    2. BHand hygiene with isolation of colonised patients
    3. CDaily chest radiographs of every inpatient on the ward
    4. DRoutine serological testing of all ward nursing staff

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17. Question 17 · Easy

    Resistance genes in hospital gram-negative bacteria most often spread between organisms on which element?

    1. APolysaccharide capsule
    2. BRibosome
    3. CPlasmid
    4. DNucleoid-associated protein

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18. Question 18 · Hard

    An infection control committee reviews the policy that applies across the whole hospital. Statements about hospital spread of resistance: 1. A single plasmid may carry resistance to several antibiotic classes. 2. Antibiotic exposure favours survival of already resistant organisms. 3. Contact precautions for colonised patients reduce transmission. 4. Resistance in one ward cannot affect another ward in the same hospital. Which combination is correct?

    1. A1 and 4 only
    2. B2 and 4 only
    3. C1, 2 and 3 only
    4. D1, 3 and 4 only

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19. Question 19 · Hard

    In the casualty of a district hospital, a shepherd from a high-altitude district has four days of high fever, cough with blood-streaked sputum and breathlessness, with bilateral patchy shadowing on the chest film and a respiratory rate of 36 per minute. Two family members have similar fever and one died at home yesterday. Marmot deaths were reported near his grazing ground a week earlier. He has received no antibiotics so far, and the nearest referral centre is six hours away by road. Which combination of actions is most appropriate immediately?

    1. AStandard precautions with azithromycin for community-acquired pneumonia
    2. BOseltamivir with isolation while influenza testing is awaited
    3. CEmpirical antituberculous treatment with discharge and follow-up
    4. DDroplet isolation, immediate streptomycin or doxycycline, notification and contact chemoprophylaxis

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20. Question 20 · Medium

    On the ninth day of a febrile illness, a man who cleans drains in Kochi has deep jaundice, severe calf myalgia, subconjunctival haemorrhage and oliguria. Bilirubin is 11 mg/dL, creatinine 4.1 mg/dL, platelets 70,000/microL and the urine shows granular casts. He gives no history of alcohol use and ultrasound shows normal-sized kidneys. Which antibiotic is most appropriate while dialysis is arranged?

    1. AOral metronidazole in divided doses
    2. BIntravenous vancomycin with dose adjustment
    3. CIntravenous penicillin or ceftriaxone
    4. DOral fluconazole for a fungal infection

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21. Question 21 · Medium

    Fever of 39 degrees C with a tender, matted, exquisitely painful swelling in the right groin develops in a man from a plague-endemic district two days after a reported rodent die-off in his village. He is tachycardic and prostrated, with a temperature of 39.4 degrees C and no cough or chest signs. Which treatment should be started?

    1. ABenzathine penicillin as a single intramuscular dose
    2. BStreptomycin, gentamicin or doxycycline
    3. COral metronidazole with clavulanate
    4. DIncision and drainage of the swelling alone

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22. Question 22 · Medium

    In a Jharkhand village, four people who cleared scrub vegetation develop fever with headache and an eschar over the trunk or groin. One of them is a woman at 20 weeks of pregnancy, with a temperature of 39 degrees C and a platelet count of 110,000/microL. The fetal heart sounds are normal and her liver enzymes are twice the upper reference limit. Which drug is preferred for her?

    1. AAzithromycin
    2. BDoxycycline for seven days
    3. CCiprofloxacin twice daily for a week
    4. DChloramphenicol by the intravenous route

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23. Question 23 · Medium

    Which statement about carriage of resistant organisms is most useful when planning hospital control measures?

    1. AColonised patients without symptoms can transmit resistant organisms
    2. BCarriage of resistant organisms usually lasts less than 24 hours
    3. COnly patients with active clinical infection transmit resistance to others
    4. DCarriage can be cleared reliably with a course of oral antibiotics

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24. Question 24 · Medium

    A man living in a crowded relief shelter in Himachal Pradesh has ten days of fever, severe headache and myalgia with a maculopapular rash that began on the trunk and spread outwards, sparing palms and soles. Body lice are found in the seams of his clothing, and two shelter residents have similar illness. Which treatment is appropriate?

    1. ADoxycycline
    2. BAmoxicillin with clavulanic acid
    3. CFluconazole for a fungal infection
    4. DMetronidazole with ornidazole

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25. Question 25 · Easy

    A farmer in Vidarbha comes to the CHC a week after skinning a cow that had died suddenly in his field. There is a painless ulcer on his right forearm with a black central eschar, surrounding small vesicles and marked non-pitting oedema up to the elbow, with tender axillary nodes and a temperature of 38.3 degrees C. Which treatment is appropriate?

    1. ATopical antiseptic dressings alone with daily review
    2. BWide surgical excision of the eschar under anaesthesia
    3. CCiprofloxacin or doxycycline
    4. DOral antifungal therapy for a cutaneous mycosis

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