Final answer:
A 17 mm zone of inhibition around a rifampin disk implies that the organism is susceptible to the antibiotic, based on comparing the measurement to standard values outlined in a reference table for interpreting disk diffusion test results.
Step-by-step explanation:
The Kirby-Bauer disk diffusion test is a method used to determine the susceptibility of a bacterium to various antimicrobial drugs by measuring the zone of inhibition (ZOI) around an antibiotic-infused disk. After placing a rifampin disk on an agar plate with bacterial inoculum and incubating it, any clear areas lacking bacterial growth—an inhibition zone—indicate susceptibility. In the scenario provided, measuring a 17 mm diameter zone of inhibition suggests that the organism is susceptible to rifampin, assuming this measurement corresponds to the standards outlined in a reference table for interpreting results.
It is essential to use a reference table of standard values to accurately report susceptibility; zones of inhibition that fall within a specific range correlate with resistance, intermediate susceptibility, or susceptibility. For rifampin, if the table indicates that a 17 mm ZOI is within the susceptible range, the organism would be reported as susceptible to the drug. Notably, the Kirby-Bauer assay does not differentiate between bacteriostatic (inhibiting bacterial growth) and bactericidal (killing bacteria) effects and cannot compare drug potencies directly.