title: Modification of interpretive breakpoints for netilmicin disk susceptibility tests with Pseudomonas aeruginosa.
abstract: Regression analysis of data correlating 30-micrograms netilmicin disk zone diameters with microdilution MICs, obtained by testing close-interval dilution steps, was performed with 77 selected strains of Pseudomonas aeruginosa, each tested in three independent laboratories. A zone of greater than or equal to 15 mm correlated with an MIC of less than or equal to 12 micrograms/ml (susceptible), and a zone of less than or equal to 12 mm correlated with an MIC of greater than 16 micrograms/ml (resistant). Additional disk tests were performed with 256 strains having known resistance mechanisms and 280 susceptible strains: the majority were appropriately categorized by these interpretive zone standards. The previously recommended standards of greater than or equal to 17 mm (MIC, less than or equal to 8.0 micrograms/ml) for the susceptible category inappropriately placed a significant number of truly susceptible P. aeruginosa strains in the intermediate category.
mesh_terms: D004352:Drug Resistance, Microbial; D005839:Gentamicins / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009428:Netilmicin / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects*
chemical_list: D005839:Gentamicins; D009428:Netilmicin