Microbiology: microorganisms, infection and specimens

30 Kerala PSC Staff Nurse Gr II practice questions on Microbiology: microorganisms, infection and specimens, part of Anatomy, Physiology and 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

   All of the following are features of the lipopolysaccharide endotoxin of Gram-negative bacteria EXCEPT:

   1. AIt can cause fever and septic shock
   2. BIt is a lipopolysaccharide of Gram-negative bacteria
   3. CIt is relatively heat stable
   4. DIt is easily converted into a toxoid

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   Answer: D · It is easily converted into a toxoid

   Endotoxin is the lipopolysaccharide (lipid A) of the outer membrane of Gram-negative bacteria, released when they die. It is heat stable and causes fever, low blood pressure and septic shock. It is poorly antigenic and cannot be made into a toxoid, so there is no toxoid vaccine against it. Exotoxins, such as tetanus and diphtheria toxins, are proteins that are turned into toxoids with formalin.

   • A: Endotoxin indeed triggers fever and septic shock.
   • B: Endotoxin is indeed the lipopolysaccharide of the Gram-negative outer membrane.
   • C: Endotoxin indeed withstands heat that destroys most exotoxins.

2. Question 2 · Medium

   A patient with smear-positive pulmonary tuberculosis is admitted. The staff should wear an N95 respirator, not just a surgical mask, because TB spreads by:

   1. AContaminated food and water
   2. BDirect skin contact
   3. CAirborne droplet nuclei
   4. DLarge respiratory droplets

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   Answer: C · Airborne droplet nuclei

   Coughing releases tiny droplet nuclei under 5 µm, which stay suspended in the air for hours and reach the alveoli when inhaled. A surgical mask does not filter such small particles reliably, while an N95 respirator fits tightly and does. Patients are kept in a well-ventilated or negative-pressure room. The patient wears a surgical mask to reduce the release of droplets.

   • A: Food-borne spread applies to bovine TB through raw milk, not pulmonary TB in a ward.
   • B: TB is not spread by skin contact.
   • D: Large droplets travel only about 1-2 metres and fall quickly; this is the route for influenza.

3. Question 3 · Medium

   Why are specimens for culture collected before the first dose of antibiotic?

   1. AThe drug turns the organism into a resistant virus
   2. BThe drug makes the sample clot in the tube
   3. CThe drug raises the risk of contamination
   4. DThe drug may stop the organism growing in culture

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   Answer: D · The drug may stop the organism growing in culture

   Even one dose of an antibiotic can reduce bacteria in blood, urine or CSF enough to make the culture negative. A false-negative culture hides the cause and the drug sensitivity of the infection. Samples are therefore taken first, but life-saving antibiotics in sepsis or meningitis should not be delayed for long. The request form should state any antibiotics already given.

   • A: Antibiotics cannot turn bacteria into viruses.
   • B: Antibiotics do not cause clotting of a sample.
   • C: Antibiotics do not increase contamination; poor technique does.

4. Question 4 · Medium

   A patient develops profuse watery diarrhoea after a long course of broad-spectrum antibiotics. The most likely organism is:

   1. AVibrio cholerae
   2. BEntamoeba histolytica
   3. CClostridioides difficile
   4. DShigella dysenteriae

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   Answer: C · Clostridioides difficile

   Broad-spectrum antibiotics destroy the normal gut flora that usually keeps C. difficile in check. The organism then multiplies and its toxins cause diarrhoea and, in severe cases, pseudomembranous colitis. The diagnosis is made by testing stool for the toxins or toxin genes. Its spores resist alcohol, so contact precautions and soap-and-water hand washing are needed.

   • A: Cholera is acquired from contaminated water or food, not from antibiotics.
   • B: Amoebiasis spreads through contaminated food and water and is not linked to antibiotics.
   • D: Shigella causes bloody dysentery spread by the faecal-oral route.

5. Question 5 · Easy

   Which bacterium is the most common member of the normal flora of human skin?

   1. AClostridium tetani
   2. BEscherichia coli
   3. CStreptococcus pyogenes
   4. DStaphylococcus epidermidis

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   Answer: D · Staphylococcus epidermidis

   Staphylococcus epidermidis, a coagulase-negative staphylococcus, lives on almost all skin surfaces. It is usually harmless, but it can enter through IV cannulas and catheters and infect prosthetic devices. It is also the commonest contaminant of blood cultures, which is why the skin is cleaned well before venepuncture. Hand hygiene reduces transient flora, but resident flora such as this always return.

   • A: Clostridium tetani lives in soil and animal intestines, not on skin.
   • B: E. coli is normal flora of the large intestine.
   • C: Streptococcus pyogenes is a throat and skin pathogen, not the main skin resident.

6. Question 6 · Hard

   A woman without urinary symptoms gives a urine sample that grows three different organisms, each at 10^3 CFU/mL. The sample took 6 hours to reach the laboratory. What does the report most likely mean?

   1. AContamination; collect a fresh midstream sample
   2. BMixed infection needing three antibiotics
   3. CSignificant bacteriuria needing antibiotics
   4. DUrinary tuberculosis needing AFB culture

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7. Question 7 · Easy

   Compared with an injection of ready-made immunoglobulin, the immunity from measles vaccine:

   1. AGives no immunological memory
   2. BActs at once but fades within months
   3. CDevelops slowly but lasts for years
   4. DIs passed on to the next generation

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8. Question 8 · Hard

   During a Nipah outbreak in Kozhikode, the first patient lived near fruit orchards, and later cases were relatives and health workers who nursed him. The natural reservoir of the virus is the:

   1. ADomestic rat
   2. BCulex mosquito
   3. CWild boar
   4. DFruit bat (Pteropus)

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9. Question 9 · Hard

   A 12-year-old has had a rising fever for 5 days, a coated tongue and a relative bradycardia. Typhoid is suspected and no antibiotic has been given. Which test is most useful now?

   1. AStool culture
   2. BBlood culture
   3. CUrine culture
   4. DWidal test on a single sample

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10. Question 10 · Easy

    In women of reproductive age, the vaginal pH is kept acidic mainly by:

    1. ACandida albicans
    2. BGardnerella vaginalis
    3. CLactobacilli (Döderlein's bacilli)
    4. DStaphylococcus aureus

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11. Question 11 · Easy

    Who is known as the father of antiseptic surgery?

    1. ALouis Pasteur
    2. BJoseph Lister
    3. CEdward Jenner
    4. DRobert Koch

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12. Question 12 · Medium

    A stool sample from a patient with suspected cholera cannot reach the laboratory for several hours. It should be sent in:

    1. ACary-Blair transport medium
    2. BBlood culture broth
    3. CRobertson's cooked meat medium
    4. DLowenstein-Jensen medium

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13. Question 13 · Hard

    A paddy field worker in Kerala has high fever, severe calf pain and red eyes a week after the monsoon floods. He has cuts on his feet. How did he most likely acquire the infection?

    1. ADrinking water contaminated by faeces
    2. BSkin cuts in water polluted by rat urine
    3. CBreathing droplets from a coughing patient
    4. DBite of an infected Aedes mosquito

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14. Question 14 · Easy

    From which site should the nurse collect urine for culture in a catheterised patient?

    1. AThe sampling port of the tubing
    2. BThe tip of the removed catheter
    3. CThe drainage bag outlet
    4. DThe junction after disconnecting the bag

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15. Question 15 · Hard

    MRSA is grown from a post-operative wound of a patient in bed 4. Two days later, the patient in bed 5, who has no wound contact with bed 4, grows the same MRSA from his IV site. What is the most likely route of spread?

    1. AHands of health care staff
    2. BInsect bites in the ward
    3. CAirborne spread through the ward
    4. DThe ward's drinking water

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16. Question 16 · Medium

    Before blood is drawn for culture, the skin is cleaned with antiseptic and allowed to dry mainly to:

    1. AMake the vein easier to see
    2. BReduce the pain of venepuncture
    3. CAvoid contamination with skin flora
    4. DPrevent haemolysis of the sample

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17. Question 17 · Medium

    What does a positive IgM antibody test against a virus usually indicate?

    1. AA booster dose given years ago
    2. BImmunity from an infection years ago
    3. CA recent or current infection
    4. DAntibody passed from the mother

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18. Question 18 · Easy

    Why does Clostridium tetani thrive in deep, dirty puncture wounds?

    1. AIt is an obligate anaerobe
    2. BIt is a microaerophile
    3. CIt is an obligate aerobe
    4. DIt needs extra carbon dioxide

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19. Question 19 · Medium

    What is the best specimen for culture of an abscess?

    1. AA dry swab of the skin surface
    2. BPus aspirated into a sterile syringe
    3. CA swab taken after antibiotics start
    4. DA swab moistened with antiseptic

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20. Question 20 · Medium

    Before giving a sputum sample for AFB, the patient is asked to rinse the mouth with water and cough deeply because:

    1. ASaliva alone is not suitable for testing
    2. BRinsing kills the oral tubercle bacilli
    3. CWater helps the bacilli to stain
    4. DCoughing raises the pH of the sputum

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21. Question 21 · Hard

    Pus from an infected surgical wound shows Gram-positive cocci in clusters. The colonies are golden yellow and coagulase positive. The organism is most likely:

    1. AStaphylococcus aureus
    2. BStaphylococcus epidermidis
    3. CStreptococcus pyogenes
    4. DMicrococcus luteus

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22. Question 22 · Medium

    Giving hepatitis B vaccine to all nursing students breaks the chain of infection at which link?

    1. AReservoir
    2. BPortal of exit
    3. CSusceptible host
    4. DMode of transmission

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23. Question 23 · Easy

    Which class of antibody crosses the placenta and protects the newborn in the first months?

    1. AIgM antibody
    2. BSecretory IgA
    3. CIgG antibody
    4. DIgD antibody

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24. Question 24 · Medium

    A food handler who has recovered from typhoid fever continues to excrete Salmonella Typhi in her stool for over a year. The organism usually persists in her:

    1. ATonsils
    2. BAppendix
    3. CUrinary bladder
    4. DGallbladder

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25. Question 25 · Easy

    Slow-growing buff colonies appear after four weeks on an egg-based slope inoculated with sputum. Which organism do they most likely belong to?

    1. ACorynebacterium diphtheriae
    2. BVibrio cholerae
    3. CNeisseria gonorrhoeae
    4. DMycobacterium tuberculosis

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