MI1.{3-9,11} | General Microbiology II: Laboratory Diagnosis, Specimens & Professionalism — Graded Quiz

A 52-year-old diabetic farmer presents with a non-healing leg ulcer. Pus collected by surface swab grows abundant Staphylococcus epidermidis. The treating surgeon asks whether S. epidermidis is the causative organism. What is the most accurate assessment of this specimen?

The CRISPR-Cas9 diagnostic platform (SHERLOCK) for detecting SARS-CoV-2 works by: (i) reverse-transcribing viral RNA to cDNA, (ii) amplifying the cDNA target, (iii) using a guide RNA to direct Cas13 to cleave the target sequence, causing collateral cleavage of a reporter molecule that produces a detectable signal. Which step exploits the same thermodynamic principle as conventional PCR?

A laboratory receives two blood culture bottles from a 68-year-old post-operative patient. One bottle (aerobic) turns positive at 22 hours; the other (anaerobic) remains negative at 5 days. Gram stain of the positive broth shows Gram-positive cocci in clusters. The most clinically important next action, from a diagnostic standpoint, is:

A microbiology department conducts an outbreak investigation after 8 patients in a surgical ICU develop nosocomial infections with a Gram-negative rod identified as Klebsiella pneumoniae. To establish whether these cases share a common source, which molecular typing method would provide the highest discriminatory power?

A 22-year-old woman with vaginal discharge is instructed to collect a high vaginal swab herself at home and bring it to the laboratory the next morning without transport medium. Which organisms would most critically be lost by this pre-analytical error?

A microbiology registrar notices that a CSF sample from a 6-year-old child was processed by the laboratory 8 hours after collection and was stored at room temperature throughout. The Gram stain appears normal, but cultures are negative at 48 hours. The child has clinical features of bacterial meningitis. What is the most likely pre-analytical explanation for this discrepancy?

An intern in a government hospital sends a stool sample for culture from a 5-year-old child with bloody diarrhoea. The sample was collected in a sterile container with no preservative and reaches the laboratory 12 hours later at room temperature. The culture grows only normal commensal flora. Which organism is most likely to have been lost due to this delay?

A laboratory technologist discovers that a colleague has mislabelled a urine sample, resulting in an MSU culture being reported as 'no significant growth' for Patient A while the actual positive result belonged to Patient A but was filed under Patient B's name. Patient B has been started on antibiotics based on this error. What is the correct ethical and professional action?

During post-test counselling for a patient who has received a positive sputum AFB smear result, the laboratory physician uses the following language: 'Your sputum shows TB germs. You have tuberculosis and must start treatment immediately or you will infect your family.' Which communication principle is most violated?

A public health official requests the HIV status of all patients tested in a district hospital laboratory over the past month to 'plan preventive programmes'. The laboratory director reviews the request. Under which condition ONLY would it be ethically appropriate to share this data?

A district public health officer is investigating a cluster of 12 cases of leptospirosis in paddy farm workers in Tamil Nadu following monsoon flooding. To confirm that these cases share the same source exposure rather than representing sporadic, geographically unrelated cases, which epidemiological approach is MOST appropriate as an initial step?

A microbiologist is reviewing a urine culture report. The specimen was collected 10 hours before reaching the laboratory and was stored at room temperature throughout. The culture shows >10⁵ CFU/mL of three different organisms: E. coli, Klebsiella pneumoniae, and Enterococcus faecalis. How should this result be interpreted?