mecA-positive methicillin-sensitive Staphylococcus aureus clinical isolates in Zenica-Doboj Canton, Bosnia and Herzegovina.

Forty-four mecA-positive and eight mecA-negative Staphylococcus aureus isolates confirmed by PCR were further tested by disc-diffusion (DD) oxacillin and cefoxitin, oxacillin Epsilon (E)-test, and oxacillin and cefoxitin minimal inhibitory concentration (MIC) Strip methicillin-resistant phenotype in S. aureus (MRSA) tests. Among 44 mecA-positive S. aureus isolates, two (4.5%) were detected as MRSA by DD-oxacillin, 17 (38.6%) by DD-cefoxitin test, and seven (15.9%) by the E-test. In the cefoxitin MIC Strip MRSA test, 19 (43.2%) isolates were resistant. In the oxacillin MIC Strip MRSA test, 18 (40.9%) isolates were resistant and 26 (59.1%) were sensitive, i. e. oxacillin-sensitive MRSA (OS-MRSA) (MIC range 0.25 <= 0.25 mg/l). Fifteen out of 26 OS-MRSA (57.7%) belonged to spa-CC 355/595, 78% of which belonged to the largest PFGE clone. Some discrepancies between the phenotypic methods for MRSA identification obtained in this study were caused by large proportion of OS-MRSA. Misidentification of OS-MRSA as MSSA might result in an appearance of highly resistant MRSA in patients treated with beta-lactam antibiotics.