Species-specific identification of methicillin resistance in staphylococci.
The ability to identify methicillin-resistant staphylococci by the disc diffusion method was evaluated using discs containing oxacillin (1, 5 and 10 micrograms), methicillin (10 micrograms) and cephalexin (30 micrograms). Strains of Staphylococcus aureus (67 strains) and coagulase-negative staphylococci (72 novobiocin-sensitive and 27 novobiocin-resistant strains) were studied using two inoculum densities (10(6) cfu/ml and 10(8) cfu/ml). Inhibitory zones were recorded after 18, 24 and 42 hours of incubation. A mecA-specific application of the polymerase chain reaction was used as a reference method. The inoculum of 10(8) cfu/ml and incubation for 24 hours were optimal for the identification of methicillin-resistant strains. However, one single disc was not sufficient for the identification of methicillin resistance in the different staphylococcal species. The mecA-positive strains of Staphylococcus aureus and novobiocin-resistant coagulase-negative species were clearly separated from the mecA-negative strains when the 5 micrograms oxacillin disc was used, whereas the 1 microgram oxacillin disc was optimal for the identification of the mecA-positive novobiocin-sensitive coagulase-negative strains.
Petersson
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Clinical Microbiology Laboratory, Lund University Hospital, Sweden.
Miörner
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D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001431:Bacteriological Techniques; D001483:Base Sequence; D002506:Cephalexin / Q000494:pharmacology; D003030:Coagulase; D004269:DNA, Bacterial / Q000032:analysis*; D004352:Drug Resistance, Microbial / Q000235:genetics*; D008712:Methicillin / Q000494:pharmacology; D016106:Methicillin Resistance / Q000235:genetics; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009675:Novobiocin / Q000494:pharmacology; D010068:Oxacillin / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D013210:Staphylococcus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification
D000900:Anti-Bacterial Agents; D003030:Coagulase; D004269:DNA, Bacterial; D009675:Novobiocin; D002506:Cephalexin; D008712:Methicillin; D010068:Oxacillin