[Evaluation of different methods for detecting resistance of staphylococcus aureus strains to methicillin]

Resistance to methicillin of 70 Staphylococcus aureus isolates from infection and 6 standard strains was evaluated by screening and disc diffusion techniques. Amongst wild S. aureus isolates 28 were identified as methicillin-susceptible (MSSA), 18 as heterogeneously resistant and 24 as homogeneously resistant to methicillin (MRSA). The best detection of methicillin-resistance was obtained by two screening techniques 1) on Mueller-Hinton agar with 6 mg oxacillin per litre and incubation for 40 hours at 37 degrees C. The evaluation of commercial test Crystal MRSA ID System proved its high usefulness in proper detection of MRSA and allowed to get results in 4 hours. Disk diffusion with 1 microgram oxacillin disk and incubation for 20 hours at 30 degrees C prove to be the most reliable out of all disc diffusion techniques studied although inferior to screening techniques.