[Comparison of several methods for detection of methicillin resistance in clinical strains of Staphylococcus sp]

108 Staphylococcus spp. strains from 300 clinical specimens from hospitalized patients were isolated. Identification and drug resistance were determined using automated ATB system. 37 S. aureus strains, 44 S. epidermides strains and 27 strains of other coagulase-negative staphylococci were cultured. Sensitivity to methicillin of S. aureus was determined with four methods: ATB system, disc-diffusion (Oxa 1 microgram), Crystal MRSA ID System and agar screen test in TSA medium with methicillin (25 micrograms/ml). 13 S. aureus strains (about 1/3 of strains) were methicillin-resistant (MRSA). Complete conformity of the results was obtained with Crystal MRSA ID, disc-diffusion and agar screen tests. In the case of three S. aureus strains the results of determination in ATB system were not consistent with the results obtained with the use of the methods mentioned above. Susceptibility to methicillin of 71 coagulase-negative strains (CNS) was determined using two methods at first: ATB and disc-diffusion. In the case of 25 methicillin-resistant strains identical results were obtained. For 20 coagulase-negative strains non-conformity with the results of these two methods was observed. As the decisive method, the agar screen test (TSA-MET) was applied. 18 of these 20 CNS strains were categorized as methicillin-resistant. Finally, 43 MRCNS (i.e. 60%) were detected among 71 coagulase-negative strains. The results of methicillin resistance determination of staphylococci in an automated system should be confirmed with a second test such as agar screen, disc-diffusion or Crystal MRSA ID System (in the case of S. aureus).