Characterization of Coagulase-Negative Staphylococci and pheno-genotypic beta lactam resistance evaluation in samples from bovine Intramammary infection

D.A Melo,C.C Motta,A.C.C M Rojas,S.M.O Coelho,B.S Soares,M.M.S Souza,I.S Coelho

doi:10.1590/1678-4162-9209

Abstract

ABSTRACT This study aimed to identify Coagulase-Negative Staphylococci (CoNS) species isolated from bovine mastitis, through phenotypic and PCR-RFLP (Restriction Fragment Length Polymorphism-Polimerase Chain Reaction) methods and to compare both techniques to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) technique. Among them, the PCR-RFLP method, using a partially conserved sequence of the groEL gene, is a promising alternative, because of its reproducibility and reliability. On the other hand, the proteomic technique MALDI-TOF MS provides an accurate and much faster diagnosis and has been increasingly employed in microbiological identification. The pheno-genotypic profiles of beta-lactam resistance were also investigated, this characterization is important, considering that the use of antimicrobials is a key element for mastitis control in dairy farms. The concordance of the phenotypic, PCR-RFLP and MALDI-TOF MS assays to identify CoNS species was 77,5% (31/40). S. chromogenes was the species most frequently isolated. Antibiotic resistance rate was relatively low, registering values of 25.5% to penicillin, 9.6% to oxacillin and 6.2% to cefoxitin. Resistance to imipenem, cephalotin and amoxicillin+clavulanate was not observed. The mecA gene and its variant were detected in 7.6% and 4,1% of the isolates respectively. The blaZ gene was found in 43.2% of the strains resistant to penicillin.

Highlights

Coagulase negative staphylococci (CoNS) are a heterogeneous group of species with limited but significant impact on dairy farms (Zadoks et al, 2011)
Two different patterns were observed for S. chromogenes strains, resulting from an intraspecific polymorphism
Sixty-eight isolates identified as S. chromogenes showed the characteristic RFLP pattern for this specie, while 16 isolates exhibited an atypical pattern, with only two fragments

Summary

Introduction

Coagulase negative staphylococci (CoNS) are a heterogeneous group of species with limited but significant impact on dairy farms (Zadoks et al, 2011). MALDI-TOF MS produces a characteristic spectrum of the analyzed microorganisms, allowing accurate identification and classification of bacterial strains This method was successfully applied to identify CoNS isolates from clinical and environmental samples (Dubois et al, 2010). Lack of susceptibility to penicillin and other beta-lactams is frequently found among CoNS isolated from cattle (Sampimon et al, 2011) This resistance is usually caused by the constitutive or induced production of a penicillinase, coded by the blaZ gene. The aims of this study were to compare the prevalence and antimicrobial susceptibility of CoNS species in bovine mastitis, identified by phenotypical tests, PCRRFLP and MALDI-TOF MS, and to determine the prevalence of mecA and blaZ genes in these strains

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Conclusion