Análise genotípica e proteômica na identificação de Staphylococcus spp. coagulase-positivos isolados do leite e sua cadeia produtiva e caracterização da resistência a beta-lactâmicos

Abstract

Staphylococcus aureus is considered the principal etiological agent of bovine mastitis. However, other coagulase-positive Staphylococcus (CPS) associated to this disease are frequently misidentified as S. aureus. This misidentification can lead to several problems in the phenotypic detection of beta-lactamic resistance. Several genotypic methods have been developed for the identification of S. aureus and other CPSs. In the other hand, proteomic identification by the MALDI-TOF MS technique for species characterization provides faster and more accurate results. S. aureus and other CPSs can show high antimicrobial resistance, especially to beta-lactams, favoring their persistence in herd environment. The monitoring of antibiotic resistance is essential in mastitis control and the use of interpretative criteria in susceptibility assays readings can be used for the detection of unusual profiles, avoiding drugs that will exert positive selective pressure in resistant strains. It can also help in the prediction of the implicated resistance mechanism, detecting phenotypic resistance markers. Two different mechanisms determine resistance to beta-lactamic antimicrobials: beta-lactamases production, encoded by the blaZ gene, and PBP2a production, a modified PBP coded by the mecA gene. Isolates expressing blaZ are frequently resistant to penicillin and ampicillin. Alternatively, mecA expression confers resistance to all beta-lactams. Recent studies, however, report that mecA detection does not have such a significant role in staphylococci isolates from bovine origin. This study was conducted to characterize, through different techniques, CPS isolates from the milk chain production, and to propose a genotipic identification fluxogram for S. aureus. Pheno-genotypic resistance profiles to beta-lactams were also evaluated. In this study, the most prevalent CPS species was S. aureus (97,9%), followed by S. hyicus (1,4%) and S. intermedius (0,7%). The genotipic identification proposed for S. aureus showed sensitivity, specificity, positive and negative predictive values of 100% compared to the proteomic technique MADLI-TOF MS. S. hyicus and S. intermedius identification was only possible by MALDI-TOF MS. Resistance to the antimicrobials tested was relatively low, as follows: oxacillin (1,4%), amoxicillin + clavulanic acid (1,4%), erythromycin (2,8%) and cephalothin (10%). There was no resistance to imipenem. In the other hand, 80,7% of the isolates were resistant to penicillin, and 41,9% of them were positive for the blaZ gene. The mecA was found in 2,7% and mecRI in 75% of the isolates susceptible to oxacillin. Neither blaZ or mecA genes were detected in some isolates phenotypically resistant to penicillin, suggesting the necessity for further investigation and a better comprehension of the mechanisms of resistence against beta-lactams staphylococci from dairy cattle.