Evaluation of phenotypic methods for methicillin resistance characterization in coagulase-negative staphylococci (CNS)

1 Fundação Faculdade Federal de Ciências Médicas de Porto Alegre, Rua Sarmento Leite 245/211, Porto Alegre, RS 90050-170, Brazil 2 Hospital Mãe de Deus, Porto Alegre, Brazil 3 Laboratório Central de Análises Clínicas da Irmandade Santa Casa de Misericórdia de Porto Alegre, RS, Brazil Correspondence Pedro A. d'Azevedo pedroaze{at}fffcmpa.tche.br Received April 9, 2004 Accepted August 5, 2004 Coagulase-negative staphylococci (CNS) are the major cause of nosocomial infections. Methicillin-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 determine the accuracy of an agar screening test (0.6 and 4 µg oxacillin ml –1 ), disc diffusion and the automated MicroScan system to characterize methicillin resistance among CNS. One hundred and seventy five strains were analysed: 41.1 % Staphylococcus epidermidis and 59.9 % other species; 69.1 % were mecA -positive. The results showed that the methods have optimal correlation with the detection of mecA gene for S. epidermidis , Staphylococcus hominis and Staphylococcus haemolyticus . However, accuracy of the tests is impaired when less common species are analysed. The only 100 % accurate test was agar screening with 4 µg oxacillin ml –1 . Abbreviations: CNS, coagulase-negative staphylococci; PBP, penicillin-binding protein.