In antibiotic susceptibility testing, what does 'Resistant' mean?

In antibiotic susceptibility testing, what does 'Resistant' mean?

• A. Drug is not effective against that organism
• B. The organism is susceptible to drug
• C. The zone of inhibition is large
• D. The drug should be used immediately

Answer: (A)

Resistant means the antimicrobial would not reliably stop or kill the organism at concentrations that can be safely achieved in the patient. In susceptibility testing, the lab compares the measured MIC or the observed zone of inhibition to established breakpoints; if the result falls into the resistant range, the drug is not considered effective for treating that organism at standard dosing. This reflects factors like the drug not reaching effective levels in the body or the organism having defenses such as enzymatic inactivation, efflux pumps, or target changes. It’s specific to the particular drug and organism pair, not a blanket statement about all antibiotics. A large zone of inhibition would indicate susceptibility, while the idea of using the drug immediately does not align with a resistant result.

Resistant means the antimicrobial would not reliably stop or kill the organism at concentrations that can be safely achieved in the patient. In susceptibility testing, the lab compares the measured MIC or the observed zone of inhibition to established breakpoints; if the result falls into the resistant range, the drug is not considered effective for treating that organism at standard dosing. This reflects factors like the drug not reaching effective levels in the body or the organism having defenses such as enzymatic inactivation, efflux pumps, or target changes. It’s specific to the particular drug and organism pair, not a blanket statement about all antibiotics. A large zone of inhibition would indicate susceptibility, while the idea of using the drug immediately does not align with a resistant result.