CLS CLS Clinical Microbiology and Immunology

Question 1

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

Accepted Answer

Pseudomonas aeruginosa

Answer

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

Question 2

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

Accepted Answer

Staphylococcus (positive) from Streptococcus (negative)

Answer

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

Question 3

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

Accepted Answer

MacConkey agar

Answer

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

Question 4

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

Accepted Answer

Syphilis

Answer

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

Question 5

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

Accepted Answer

Proteus mirabilis

Answer

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

CLS - Certified Laboratory Professional Practice Test

CLS - Certified Laboratory Professional Practice Test

CLS CLS Clinical Microbiology and Immunology