If you use an expired antibiotic disk in a KB assay, what is the likely result?

Prepare for the CAMLPR Microbiology Test. Utilize flashcards and engaging multiple-choice questions, each equipped with descriptions and explanations. Ready yourself for an excellent performance!

In a Kirby-Bauer disk diffusion test, the size of the inhibition zone depends on how much active antibiotic is released from the disk. An expired disk often has reduced potency, so it releases less drug into the agar. That makes the bacteria appear less inhibited, resulting in a smaller zone or no zone. Because interpretation of susceptibility relies on zone size, this can be read as resistance even though the organism might be susceptible if the disk were still potent. So, the likely outcome is the organism being labeled falsely resistant.