CLS Clinical Microbiology and Immunology Flashcards

Which organism is identified by oxidase-positive results, blue-green pigment (pyocyanin), and a grape-like odor?

Answer: Pseudomonas aeruginosa

Pseudomonas aeruginosa produces pyocyanin (blue-green pigment), has a characteristic grape-like odor, is oxidase-positive, and does not ferment lactose.

The catalase test is used to differentiate which two clinically important genera?

Answer: Staphylococcus (positive) from Streptococcus (negative)

The catalase test differentiates Staphylococcus (catalase-positive, bubbles with H₂O₂) from Streptococcus (catalase-negative, no bubbles).

Which agar medium is both selective (for gram-negatives) and differential (for lactose fermentation)?

Answer: MacConkey agar

MacConkey agar selects for gram-negative bacteria using bile salts and crystal violet, and differentiates lactose fermenters (pink colonies) from non-fermenters (colorless).

The VDRL (Venereal Disease Research Laboratory) test is used to screen for which sexually transmitted infection?

Answer: Syphilis

The VDRL is a non-treponemal flocculation test that screens for syphilis by detecting reagin antibodies produced in response to Treponema pallidum infection.

Which gram-negative rod produces urease, causes struvite kidney stones, and displays 'swarming' motility on agar?

Answer: Proteus mirabilis

Proteus mirabilis hydrolyzes urea with urease, raising urine pH and promoting struvite (magnesium ammonium phosphate) stone formation, and characteristically swarms on non-inhibitory agar.

What is the gold standard method for definitive diagnosis of Mycobacterium tuberculosis infection?

Answer: Mycobacterial culture

Mycobacterial culture remains the gold standard because it confirms viable organisms and allows antibiotic susceptibility testing for drug-resistant TB.