Gentamicin and amikacin disk susceptibility tests with Pseudomonas aeruginosa: definition of minimal inhibitory concentration correlates for susceptible and resistant categories.

With currently recommended disk susceptibility tests, minimal inhibitory concentration correlates for amikacin were greater than 16 micrograms/ml for resistance and less than or equal to 12 micrograms/ml (not less than or equal to 8 micrograms/ml) for susceptibility. For gentamicin, they were greater than 8 micrograms/ml for resistance and less than or equal to 6 micrograms/ml (not less than or equal to 4 micrograms/ml) for susceptibility. Minor discrepancies between disk tests and minimal inhibitory concentration determinations will occur if only doubling dilutions of drug are used for measuring minimal inhibitory concentration values.