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MI1.{3-9,11} | General Microbiology II: Laboratory Diagnosis, Specimens & Professionalism — Practice Quiz
Practice
10 questions · Untimed · Unlimited attempts
Click any question card to reveal the correct answer.
A 35-year-old woman is suspected to have pulmonary tuberculosis. Her sputum is sent for PCR, which returns positive for Mycobacterium tuberculosis. She had completed a 6-month anti-TB course 3 months ago and is now asymptomatic. What is the most likely explanation for the positive PCR result?
A
Treatment failure with drug-resistant TB
B
Persistence of dead mycobacterial DNA after successful therapy
✓
C
Re-infection with a new TB strain
D
PCR cross-reactivity with non-tuberculous mycobacteria
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In a district hospital microbiology laboratory, a blood culture from a febrile patient turns positive after 18 hours of incubation. Which of the following is the most appropriate immediate next step?
A
Report the result as 'blood culture positive' and await final identification
B
Perform a Gram stain on the positive broth and call the treating clinician with the result
✓
C
Subculture onto blood agar and wait 48 hours for colony identification before reporting
D
Repeat the blood culture from the same site to confirm contamination
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A medical student is asked to collect a midstream urine (MSU) sample from a 28-year-old woman with suspected urinary tract infection. Which instruction to the patient is MOST critical before collection?
A
Collect the first 10 mL of urine to capture organisms from the urethra
B
Clean the periurethral area with a sterile wipe, discard the initial stream, then collect mid-stream urine in a sterile container
✓
C
Collect the specimen any time of day in a clean household container
D
Refrigerate the specimen for up to 48 hours before transport
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Which of the following staining techniques is MOST appropriate for the rapid identification of Cryptococcus neoformans in cerebrospinal fluid?
A
Gram stain
B
Ziehl-Neelsen stain
C
India ink preparation
✓
D
Giemsa stain
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A throat swab for culture is collected from a 10-year-old child with fever and exudative pharyngitis. The sample reaches the microbiology laboratory 6 hours later without a transport medium. What is the most likely consequence?
A
Overgrowth of Streptococcus pyogenes masking other organisms
B
Drying and death of fastidious organisms such as Haemophilus influenzae and Neisseria species, causing false-negative results
✓
C
No significant effect if the swab was collected with a nylon-flocked swab
D
The specimen remains valid for 24 hours as long as it is refrigerated
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Which of the following best describes the epidemiological triad as applied to the spread of tuberculosis in an overcrowded Indian slum?
A
Agent: M. tuberculosis; Host: immunocompetent individuals only; Environment: any climate
B
Agent: M. tuberculosis; Host: persons with poor nutrition/immunosuppression; Environment: overcrowding, poor ventilation facilitating airborne spread
✓
C
Agent: M. tuberculosis; Host: elderly patients; Environment: hospital settings only
D
Agent: HIV; Host: TB patients; Environment: tropical climate
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A junior resident in the microbiology laboratory is processing samples. She handles a high-risk HIV specimen with bare hands, arguing it is 'just a tube.' Which principle of laboratory professionalism does this most directly violate?
A
Confidentiality of laboratory results
B
Universal precautions — treating all specimens as potentially infectious
✓
C
Informed consent for laboratory testing
D
Pre-test patient counselling
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A clinician calls the microbiology laboratory requesting the HIV rapid test result for one of their patients. A nurse passing by overhears the conversation and asks the lab technician about the result. Which is the most appropriate action?
A
Share the result with the nurse because she is healthcare staff
B
Decline to share the result with the nurse and communicate results only through secure, need-to-know channels
✓
C
Share the result but ask the nurse to keep it confidential
D
Document the result in the ward register for all staff to access
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ELISA is used as a screening test for HIV infection. A blood donor tests ELISA-positive. What is the most appropriate next step before informing the donor of the result?
A
Immediately notify the donor in the waiting room
B
Repeat the ELISA on the same sample and, if reactive, perform Western blot or another confirmatory test
✓
C
Start the donor on antiretroviral therapy immediately
D
Discard the result as a false positive and recall the donor in 3 months
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A medical intern is explaining the procedure for sputum collection to a patient with suspected pulmonary TB. The patient speaks only Tamil. The intern, who does not speak Tamil, proceeds to collect the sample without interpretation. Which communication competency is most deficient in this interaction?
A
Failure to document the sample collection in the case notes
B
Failure to obtain informed co-operation through language-appropriate communication before specimen collection
✓
C
Failure to wear gloves during specimen collection
D
Failure to order the correct test
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