Which laboratory test grows bacteria from an infected area to identify the organism and determine antibiotic sensitivity?

• A. Gram Stain
• B. Urine Culture
• C. PCR
• D. Culture and Sensitivity (C&S)

Answer: (D)

Growing the organism in culture provides live bacteria to identify what species is present and to test how it responds to different antibiotics. This is done through culture followed by susceptibility testing (often disk diffusion or broth microdilution), which yields a profile of antibiotics that can effectively inhibit or kill the organism. Without culture, you might know there’s bacteria, but you wouldn’t have a reliable guide to which drugs will work.

Rapid Gram staining can tell you the general category of bacteria (whether Gram-positive or Gram-negative) and some features, but it doesn’t reveal antibiotic susceptibility. A urine culture specifically targets bacteria in urine to diagnose a urinary tract infection, and while it cultures the organism, susceptibility testing isn’t necessarily done unless the test is specifically ordered as part of a sensitivity workup. PCR detects genetic material and can identify pathogens or resistance genes quickly, but it does not measure how the organism grows in the presence of antibiotics or provide a phenotypic susceptibility profile. Hence, the test that both grows the bacteria and determines antibiotic sensitivity is culture and sensitivity.