What is the purpose of a check culture in antimicrobial susceptibility testing?

• A. To verify media, inoculum, and procedures by testing a known organism with a known expected result
• B. To identify patient disease
• C. To compare antibiotic prices
• D. To determine sample source

Answer: (A)

Check culture in antimicrobial susceptibility testing serves as a quality-control step using a well-characterized reference organism with a known response to antibiotics. Its main purpose is to verify that the media, inoculum size, antibiotic potency, and the testing procedures (disk diffusion or dilution methods) are working correctly under the lab’s conditions by producing results within expected ranges. Running this organism helps catch problems with reagents, incubator conditions, timing, or technique before patient isolates are tested, ensuring that reported results are accurate and reliable. This approach is about validating the testing process, not about diagnosing a patient, comparing prices, or determining where a sample came from.