[Short communication: Determination of methicillin resistance in staphylococci with different methods and detection of multiple antibiotic resistance].

The aims of this study were to determine the methicillin resistance of a total of 256 staphylococcus strains [213 Staphylococcus aureus and 43 coagulase negative staphylococci (CNS)], isolated from different clinical samples and hospital environmental specimens by different methods and to detect multiple antibiotic resistance in these isolates. Methicillin resistance of staphylococci was investigated by using oxacillin agar screening (OAS), oxacillin disk diffusion (ODD), cefoxitin disk diffusion (CDD), PBP2a latex agglutination (LA) and microdilution tests. The resistance of the strains against penicillin G, amoxycillin/clavulanate, cephalothin, tetracycline, erythromycin, fusidic asid, ofloxacin, vancomycin, co-trimoxazole and gentamicin was investigated by standard disk diffusion method. As a result, 152 (71.3%) S. aureus and 30 (69.7%) CNS isolates were found to be methicillin-resistant with the use of OAS and PBP2a LA tests, respectively. The numbers of the isolates which were detected as methicillin-resistant and methicillin-susceptible were 182 and 74 by OAS; 183 and 73 by ODD; 181 and 75 by SDD; 180 and 76 by PBP2a LA; 183 and 73 by microdilution tests, respectively. There was no statistically significant differences-between the results obtained by all of the methods (p > 0.05), however the sensitivity of PBP2a LA test was lower in the detection of methicillin resistance in S. aureus strains. CDD test which was found to be as sensitive as ODD test, may be preferred in the detection of methicillin resistance in staphylococci. In our study staphylococci which were sensitive to methicillin, were also found generally sensitive to the other antibiotics, whereas staphylococci which were resistant to methicillin were also resistant to the other antibiotics. The difference between methicillin sensitive and resistant staphylococci in terms of the rates of resistance against other antibiotics was found statistically significant with the exception of fusidic acid (p < 0.05). The resistance rates of isolates for fusidic acid were very low and all of the strains were susceptible to vancomycin. In conclusion, for better determination of methicillin resistance, agar screening test which is proposed as a confirmatory test by CLSI, should be used when necessary.