CLT CLT Microbiology & Urinalysis 2 — Questions and Answers
Question 1: Waxy casts found in urine sediment are associated with which clinical condition?
- Early glomerulonephritis
- Severe chronic renal failure (Correct answer)
- Acute cystitis
- Dehydration
Correct answer: Severe chronic renal failure
Waxy casts form from the degeneration of granular casts in nephrons with very slow urine flow and indicate severe chronic renal disease.
Question 2: A urine dipstick is positive for nitrites. What does this finding indicate?
- Renal tubular acidosis
- The presence of nitrite-reducing bacteria (gram-negative organisms) (Correct answer)
- Fungal infection
- Proteinuria
Correct answer: The presence of nitrite-reducing bacteria (gram-negative organisms)
Many gram-negative bacteria reduce dietary nitrates to nitrites; a positive nitrite result on dipstick suggests a bacterial UTI caused by gram-negative organisms.
Question 3: Which agar is used for the isolation of Neisseria gonorrhoeae and other fastidious organisms?
- MacConkey agar
- Mannitol salt agar
- Thayer-Martin agar (Correct answer)
- Eosin methylene blue agar
Correct answer: Thayer-Martin agar
Thayer-Martin agar is an enriched selective medium containing antibiotics (VCN — vancomycin, colistin, nystatin) that inhibit normal flora while supporting growth of Neisseria species.
Question 4: In urine microscopy, which finding is most associated with acute glomerulonephritis?
- Hyaline casts
- RBC casts (Correct answer)
- Epithelial cell casts
- Mucus threads
Correct answer: RBC casts
RBC casts indicate that red blood cells have leaked through damaged glomeruli and formed casts in the tubules, which is pathognomonic for glomerulonephritis.
Question 5: The coagulase test is used to differentiate which two clinically important Staphylococcus species?
- S. aureus (positive) from S. epidermidis (negative) (Correct answer)
- S. saprophyticus from S. haemolyticus
- S. aureus from S. pyogenes
- S. epidermidis from S. saprophyticus
Correct answer: S. aureus (positive) from S. epidermidis (negative)
Coagulase production distinguishes the pathogenic S. aureus (coagulase-positive) from coagulase-negative staphylococci such as S. epidermidis.
Question 6: When a urine specimen for culture cannot be processed within 2 hours, what is the recommended storage condition?
- Room temperature up to 24 hours
- Refrigeration at 2–8°C for up to 24 hours (Correct answer)
- Freezing at -20°C immediately
- Addition of boric acid and room temperature storage for 72 hours
Correct answer: Refrigeration at 2–8°C for up to 24 hours
Refrigeration at 2–8°C preserves urine specimens for culture for up to 24 hours by inhibiting bacterial growth without altering colony counts.
CLT CLT Microbiology & Urinalysis 2
Waxy casts found in urine sediment are associated with which clinical condition?