ABSTRACT
Coagulase-negative staphylococci [CNS] are one of the major causes of nosocomial infections. Methicillin [oxacillin] resistant strains are particularly important because they narrow therapeutic options. Detecting methicillin resistance among CNS has been a challenge for years. The objective of this study was to evaluate the ability and accuracy of four phenotypic methods, disk diffusion [DD]; agar screening plate with 6 micro g of oxacillin per ml [OXA]; E-test and the MRSA-Screen latex agglutination test [Denka-Seiken, Tokyo, Japan], to determine the susceptibility of CNS to oxacillin. The methods were evaluated by using the presence of the mecA gene, as detected by PCR, as the "gold standard". One hundred and ninety seven strains of CNS of 7 species were analysed. 49.2% were mecA positive. For the different methods evaluated, the sensitivities and specificities were as follows: for disk diffusion, 93.8 and 93%, respectively; for the agar screen test 95.9 and 98%, respectively; for E-test, 100 and 95%, respectively; and for the slide latex agglutination test, 96.9 and 100%, respectively. The latex agglutination test sensitivity was increased to 100% when retested after induction. In conclusion, all of the phenotypic methods evaluated in the present study appeared to perform very well for the detection of oxacillin resistance in CNS. The MRSA-Screen latex agglutination test was not only the most sensitive, specific and accurate method but also rapid and technically simple method to be applied in routine laboratories for the detection of oxacillin resistance which is mediated by the mecA gene