A newly joined nurse has these pre-employment results: HBsAg negative, total anti-HBc negative, anti-HBs 85 mIU/mL. These results mean she is:

Immune because of hepatitis B vaccination

Chronically infected with hepatitis B

Immune because of a past natural infection

Susceptible and in need of vaccination

Which pairing of item and sterilisation method is correct?

Glass syringes and powders: hot air oven

Rubber catheters: hot air oven at 160 °C

Fibre-optic endoscope: autoclave at 134 °C

Surgical gowns and linen: hot air oven

A surgical patient, five days after operation, is afebrile with a normal WBC count. Of two blood culture sets drawn at the same time from different sites, one bottle grows coagulase-negative staphylococci after 3 days; the other set is sterile. The most likely explanation is:

Skin contamination during collection

Bacteraemia with Staphylococcus aureus

A line-related septicaemia needing vancomycin

On a Ziehl-Neelsen stained sputum smear reported as positive, the tubercle bacilli appear as:

Pink rods on a purple background

Purple cocci in grape-like clusters

A stool sample is sent to look for motile trophozoites of Entamoeba histolytica in a patient with bloody diarrhoea. The nurse should make sure it is:

Examined within about 30 minutes of passage

Placed in formalin before microscopy

Refrigerated overnight before it is sent

Collected from stool mixed with urine

Microbiology, immunity and laboratory specimens

18 AIIMS NORCET (Nursing Officer) practice questions on Microbiology, immunity and laboratory specimens, part of Anatomy, Physiology and Microbiology. The first 18 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A newly joined nurse has these pre-employment results: HBsAg negative, total anti-HBc negative, anti-HBs 85 mIU/mL. These results mean she is:
1. AChronically infected with hepatitis B
2. BImmune because of a past natural infection
3. CImmune because of hepatitis B vaccination
4. DSusceptible and in need of vaccination
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Answer: C · Immune because of hepatitis B vaccination
The vaccine contains only the surface antigen, so a vaccinated person makes anti-HBs but not anti-HBc. Anti-HBc appears only after real infection, so a negative anti-HBc with a protective anti-HBs (at least 10 mIU/mL) means vaccine immunity. Past infection would show both anti-HBc and anti-HBs, and chronic infection would show HBsAg for over six months. She needs no further doses.
- A: Chronic infection needs a positive HBsAg, which is negative here.
- B: Natural infection would also give a positive anti-HBc, which is negative here.
- D: An anti-HBs of 85 mIU/mL is protective, so she is not susceptible.
Question 2 · Hard
Which pairing of item and sterilisation method is correct?
1. ARubber catheters: hot air oven at 160 °C
2. BFibre-optic endoscope: autoclave at 134 °C
3. CGlass syringes and powders: hot air oven
4. DSurgical gowns and linen: hot air oven
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Answer: C · Glass syringes and powders: hot air oven
The hot air oven (160 °C for 2 hours) suits items that moist heat cannot penetrate or would damage, such as glassware, powders, oils and sharp metal instruments. Rubber and plastics melt in dry heat and are autoclaved if heat-stable or sterilised with ethylene oxide. Flexible endoscopes are heat-sensitive and are reprocessed by high-level disinfection, for example with 2% glutaraldehyde. Fabrics such as gowns and linen are autoclaved, because steam penetrates them and dry heat would scorch them.
- A: Rubber is damaged by 160 °C dry heat; it is autoclaved or gas-sterilised.
- B: Fibre-optic endoscopes are damaged by steam and need chemical high-level disinfection.
- D: Fabrics are sterilised by autoclaving; dry heat at 160 °C chars them.
Question 3 · Hard
A surgical patient, five days after operation, is afebrile with a normal WBC count. Of two blood culture sets drawn at the same time from different sites, one bottle grows coagulase-negative staphylococci after 3 days; the other set is sterile. The most likely explanation is:
1. ASkin contamination during collection
2. BBacteraemia with Staphylococcus aureus
3. CA line-related septicaemia needing vancomycin
4. DEarly infective endocarditis
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Answer: A · Skin contamination during collection
Coagulase-negative staphylococci live on normal skin and are the commonest blood culture contaminants. Growth in only one of two sets, late growth, and a well patient with no fever and a normal count all point to contamination. True CoNS bacteraemia usually shows in several sets, often with a prosthetic device or central line. Good skin antisepsis with chlorhexidine-alcohol that is allowed to dry prevents most contaminants.
- B: S. aureus is coagulase-positive, so it does not match this isolate.
- C: A single positive set in a well patient does not justify treating line sepsis.
- D: Endocarditis gives continuous bacteraemia, so multiple sets would be positive in an unwell patient.
Question 4 · Easy
On a Ziehl-Neelsen stained sputum smear reported as positive, the tubercle bacilli appear as:
1. ABlue rods on a red background
2. BPink rods on a purple background
3. CPurple cocci in grape-like clusters
4. DRed rods on a blue background
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Answer: D · Red rods on a blue background
Mycobacteria have a cell wall rich in mycolic acid, which holds the hot carbol fuchsin even after acid-alcohol is applied. They therefore stay red while other organisms and cells take the blue methylene blue counterstain. This is the basis of sputum smear microscopy for TB. M. leprae is also acid-fast, though more weakly.
- A: This reverses the colours: the bacilli hold the red carbol fuchsin and the background is blue.
- B: A purple background is not part of the ZN stain; the counterstain is methylene blue.
- C: Purple cocci in clusters describe staphylococci on a Gram stain.
Question 5 · Medium
A stool sample is sent to look for motile trophozoites of Entamoeba histolytica in a patient with bloody diarrhoea. The nurse should make sure it is:
1. AExamined within about 30 minutes of passage
2. BPlaced in formalin before microscopy
3. CRefrigerated overnight before it is sent
4. DCollected from stool mixed with urine
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Answer: A · Examined within about 30 minutes of passage
Trophozoites of E. histolytica die and stop moving soon after the stool cools, and motility with ingested red cells is the key feature that identifies them. So a fresh, warm sample is examined within about 30 minutes, or placed in a preservative such as PVA if a delay is unavoidable. Urine, water and barium also destroy them. Cysts are hardier and can be seen in formed stools.
- B: Formalin kills trophozoites, so motility can no longer be seen.
- C: Cooling kills trophozoites and stops their motility, so they are missed.
- D: Urine destroys trophozoites and dilutes the sample.
Question 6 · Medium
For sputum microscopy and testing for pulmonary tuberculosis, the most useful specimen is:
1. ASputum pooled from several days in one jar
2. BAn early-morning sample from a deep cough
3. CSaliva collected after rinsing the mouth
4. DThroat swab taken during the evening
Answer and explanation in LearnFree account
Question 7 · Easy
Blood for culture in a patient with suspected sepsis should ideally be drawn:
1. AOne hour after the first antibiotic
2. BFrom the existing IV cannula line
3. CBefore the first dose of antibiotic
4. DOnly when the temperature has settled
Answer and explanation in LearnFree account
Question 8 · Easy
The standard autoclave cycle for wrapped surgical instruments uses saturated steam at:
1. A160 °C, dry heat, for 2 hours
2. B100 °C, 0 psi, for 30 minutes
3. C121 °C, 15 psi, for 15 minutes
4. D80 °C, 5 psi, for 10 minutes
Answer and explanation in LearnFree account
Question 9 · Medium
A cerebrospinal fluid sample has been collected from a child with suspected bacterial meningitis. How should it be handled before it reaches the microbiology laboratory?
1. AFrozen at -20 °C to preserve it
2. BHeld on the ward until the next round
3. CRefrigerated at 4 °C until sent
4. DSent at once at room temperature
Answer and explanation in LearnFree account
Question 10 · Easy
A tuberculin (Mantoux) skin test is injected intradermally. The induration should be read after:
1. A6-12 hours
2. B15-20 minutes
3. C7-10 days
4. D48-72 hours
Answer and explanation in LearnFree account
Question 11 · Hard
A staff nurse sustains a needlestick injury from a patient who is HBsAg-positive. Her records show a full hepatitis B vaccine course with a documented anti-HBs level of 120 mIU/mL. The appropriate hepatitis B management is:
1. AHepatitis B immunoglobulin plus a vaccine booster
2. BNo further hepatitis B treatment is needed
3. CHepatitis B immunoglobulin twice, a month apart
4. DRestart the full three-dose vaccine schedule
Answer and explanation in LearnFree account
Question 12 · Medium
After a contaminated municipal water supply, several people in a town develop jaundice. One of them, a woman 32 weeks pregnant, is at particular risk of fulminant liver failure. The most likely virus is:
1. AHepatitis C virus
2. BHepatitis B virus
3. CHepatitis D virus
4. DHepatitis E virus
Answer and explanation in LearnFree account
Question 13 · Easy
In a Gram-stained smear, Gram-positive bacteria appear purple because they:
1. AAbsorb iodine as their only bound stain
2. BHave a waxy coat that holds carbol fuchsin
3. CRetain crystal violet in a thick peptidoglycan wall
4. DTake up safranin through an outer lipid membrane
Answer and explanation in LearnFree account
Question 14 · Medium
A patient using an inhaled corticosteroid for asthma develops creamy white patches on the tongue and palate that can be scraped off, leaving a red, raw surface. The most likely organism is:
1. AHerpes simplex virus
2. BStreptococcus pyogenes
3. CCandida albicans
4. DAspergillus fumigatus
Answer and explanation in LearnFree account
Question 15 · Hard
A 19-year-old hostel student has fever, neck stiffness and a non-blanching purpuric rash. Gram stain of his CSF shows Gram-negative diplococci inside neutrophils. Which isolation precaution should the nurse start?
1. AStandard precautions alone, as the disease is not spread
2. BAirborne precautions in a negative-pressure room
3. CContact precautions with gown and gloves only
4. DDroplet precautions until 24 hours of effective antibiotic
Answer and explanation in LearnFree account
Question 16 · Medium
A clean-catch midstream urine sample for culture is collected at 10 pm, but the laboratory will receive it only the next morning. The nurse should:
1. AKeep it in an incubator at 37 °C
2. BRefrigerate it at 2-8 °C until it is sent
3. CAdd a drop of spirit to preserve it
4. DLeave it at room temperature overnight
Answer and explanation in LearnFree account
Question 17 · Medium
A labourer with a deep, soil-contaminated wound and no record of tetanus immunisation is given tetanus immunoglobulin. The protection it gives is:
1. ANaturally acquired active immunity
2. BArtificially acquired passive immunity
3. CArtificially acquired active immunity
4. DNaturally acquired passive immunity
Answer and explanation in LearnFree account
Question 18 · Medium
Blood culture bottles, a sodium citrate (coagulation) tube and an EDTA (complete blood count) tube are to be filled from one venepuncture. The correct order of filling is:
1. ACulture bottles, then citrate, then EDTA
2. BCulture bottles, then EDTA, then citrate
3. CEDTA, then citrate, then culture bottles
4. DCitrate, then EDTA, then culture bottles
Answer and explanation in LearnFree account

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Microbiology, immunity and laboratory specimens

A newly joined nurse has these pre-employment results: HBsAg negative, total anti-HBc negative, anti-HBs 85 mIU/mL. These results mean she is:

Which pairing of item and sterilisation method is correct?

A surgical patient, five days after operation, is afebrile with a normal WBC count. Of two blood culture sets drawn at the same time from different sites, one bottle grows coagulase-negative staphylococci after 3 days; the other set is sterile. The most likely explanation is:

On a Ziehl-Neelsen stained sputum smear reported as positive, the tubercle bacilli appear as:

A stool sample is sent to look for motile trophozoites of Entamoeba histolytica in a patient with bloody diarrhoea. The nurse should make sure it is:

For sputum microscopy and testing for pulmonary tuberculosis, the most useful specimen is:

Blood for culture in a patient with suspected sepsis should ideally be drawn:

The standard autoclave cycle for wrapped surgical instruments uses saturated steam at:

A cerebrospinal fluid sample has been collected from a child with suspected bacterial meningitis. How should it be handled before it reaches the microbiology laboratory?

A tuberculin (Mantoux) skin test is injected intradermally. The induration should be read after:

A staff nurse sustains a needlestick injury from a patient who is HBsAg-positive. Her records show a full hepatitis B vaccine course with a documented anti-HBs level of 120 mIU/mL. The appropriate hepatitis B management is:

After a contaminated municipal water supply, several people in a town develop jaundice. One of them, a woman 32 weeks pregnant, is at particular risk of fulminant liver failure. The most likely virus is:

In a Gram-stained smear, Gram-positive bacteria appear purple because they:

A patient using an inhaled corticosteroid for asthma develops creamy white patches on the tongue and palate that can be scraped off, leaving a red, raw surface. The most likely organism is:

A 19-year-old hostel student has fever, neck stiffness and a non-blanching purpuric rash. Gram stain of his CSF shows Gram-negative diplococci inside neutrophils. Which isolation precaution should the nurse start?

A clean-catch midstream urine sample for culture is collected at 10 pm, but the laboratory will receive it only the next morning. The nurse should:

A labourer with a deep, soil-contaminated wound and no record of tetanus immunisation is given tetanus immunoglobulin. The protection it gives is:

Blood culture bottles, a sodium citrate (coagulation) tube and an EDTA (complete blood count) tube are to be filled from one venepuncture. The correct order of filling is: