title: Reliability of high-content disks and modified broth dilution tests for detecting staphylococcal resistance to the penicillinase-resistant penicillins.
abstract: In vitro susceptibility tests were performed with 271 isolates of Staphylococcus species (204 Staphylococcus aureus), including 110 strains resistant to the penicillinase-resistant penicillins. Disks containing 5 or 10 micrograms of methicillin, 1 or 4 micrograms of oxacillin, and 1 or 4 micrograms of nafcillin were evaluated. After a full 24 h of incubation at 35 degrees C, tests with 1-microgram oxacillin disks provided optimal results. Use of the more potent oxacillin, nafcillin, or methicillin disks only increased the number of false-susceptible test results. For broth microdilution tests, 2% NaCl should be added to cation-supplemented Mueller-Hinton broth, and MICs should be recorded after a full 24 h at 35 degrees C. Microdilution tests with oxacillin in broth with 2% NaCl were more reliable than similar tests with methicillin.
mesh_terms: D003470:Culture Media; D008712:Methicillin / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D009254:Nafcillin / Q000494:pharmacology; D010068:Oxacillin / Q000494:pharmacology; D010403:Penicillin Resistance; D010405:Penicillinase / Q000378:metabolism; D011237:Predictive Value of Tests; D012965:Sodium Chloride; D013210:Staphylococcus / Q000187:drug effects* / Q000201:enzymology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000201:enzymology
chemical_list: D003470:Culture Media; D012965:Sodium Chloride; D009254:Nafcillin; D010405:Penicillinase; D008712:Methicillin; D010068:Oxacillin