AGAR DISK DIFFUSION METHOD FOR THE DETERM INATION OF PHENOTYPIC CLASSES IN METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS

Four stable classes of phenotypic expression in methicillin resistant Staphylococcus aureus were described : three of them showed heterogene ous resistance. The fourth was homogeneous. Methicillin resistance dep end on the gene mecA encoding an altered penicillin-binding protein. T he phenotypic expression was controlled by chromosomic factors (fem an d aux genes) and was modified by test conditions : (temperature - pH - NaCl 4%). The conventional method for determination of these differen t classes was the population analysis method using methicillin as anti biotic indicator. This fastidious method cannot use in routine laborat ory. In this work, the authors developed a common method using the dif fusion agar method. Four antibiotic disks (methicillin 2.5, 15, 100 mu g oxacillin 30 mug) and three incubation temperatures (30 - 35 - 40-de grees-C). The determination of the penotypic classes could be an epide miologic marker for the survey of epidemic MRSA in hospital.