Detection of methicillin resistance in hospital environmental strains of coagulase-negative staphylococci.

The aim of this study was to evaluate methicillin resistance detection methods currently used when studying coagulase-negative staphylococci (CONS). The resistance to oxacillin of 142 strains from seven species of CoNS isolated from the Intensive Care Unit environments was tested. The methods used were: disc diffusion test with cefoxitin (FOX30) and oxacillin (OX1), oxacillin agar screen test with 6 mg/l of oxacillin (MHOXA), latex test for PBP2a (LA) and detection of mecA via PCR. One hundred and one isolates were methicillin-resistant in at least one of methods used, but only 74 were mecA-positive. Of the 68 mecA-negative strains: two were positive by OX1, the LA and MHOXA methods; three by the LA and MHOXA; and 22 only by OX1 test. Most of these strains were from the novobiocin-resistant CoNS group. The results obtained for all tested strains using FOX30 showed complete concordance with the presence of the mecA gene.