Caracterização fenotípica da resistência aos antimicrobianos e detecção do gene mecA em Staphylococcus spp. coagulasenegativos isolados de amostras animais e humanas

Abstract

Coagulasenegative staphylococci (SCN) take part of normal microbiota. Although it has been considered saprophytic, nowadays there is a concern about its pathogenic potential.Nevertheless, all advance in SCN identification assays, these microorganisms are continually neglected in laboratorial routine of infectious diseases, because of the wide range of species. In spite of the difficulties, it is necessary to make an appropriated species identification in order to differentiate the potential pathogenic agents and to determine its antimicrobial susceptibility pattern. Resistance in SCN is related to the presence of mecA gene, which expresses a heterogeneous pattern that can be detected through diverse phenotypics tests. In this study, 72 SCN isolates obtained from external ear conducts of dogs, bovine mastitis and human nosocomial infections were evaluated. Staphylococcus xylosus was the most prevalent microorganism in animal and S. cohnii subsp.urealyticus in human sample. The antimicrobial resistance patterns were evaluated through disc diffusion test, and a high level of resistance to penicillin and ampicillin were detected. The most efficient antibiotics evaluated were gentamicin, vancomicin and the association ampicillin+sulbactam. Oxacillin resistance was phenotypically detected by modified disc diffusion test, agar screen, broth microdilution and agar dilution. Presence of mecA gene where detected in 5,55% of the isolates by Polimerase Chain Reaction (PCR). Correlation with the detection of mecA gene was used as gold standard for evaluation of sensitivity and specificity of phenotypical assays. The low number of mecA positives isolates did not allowed the association between cefoxitin and oxacillin resistance as a test to detect the presence this gene. The broth microdilution and agar dilution tests presented the best accuracy in phenotypic detection of the oxacillin resistance.