A breakpoint is a chosen concentration (mg/L) of an antibiotic which defines whether a species of bacteria is susceptible or resistant to the antibiotic. If the MIC is less than or equal to the susceptibility breakpoint the bacteria is considered susceptible to the antibiotic. If the MIC is greater than this value the bacteria is considered intermediate or resistant to the antibiotic.
Isolate is a pure culture of bacteria, all the same species and strain.
MIC is the Minimum Inhibitory Concentration. This is the lowest concentration of an antibiotic required to inhibit the growth of an organism. To identify the MIC the bacteria are added to plates containing varying concentrations of the antibiotic. The concentration of antibiotic is doubled in each successive plate and the MIC is found by identifying the first plate in which there is no visible colony after an incubation period.