Antimicrobial resistance of Staphylococcus spp. isolated from clinical and subclinical bovine mastitis: phenotypic analysis, gene expression and relationship with the presence of genes encoding adhesins and biofilm

Abstract

Mastitis is a major challenge in dairy farming, as it is one of the diseases that most affect the cattle and causes great economic impact. Bacteria are important agents associated with the disease, and the most commonly found are those of the Staphylococcus genus, associated with both the clinical and subclinical manifestations. Antimicrobial therapy is usually required as treatment, helping the animal defenses to eliminate the invading agents, therefore, it is of utmost importance to monitor the susceptibility of pathogens to antimicrobial agents. Since resistance to drugs has become frequent, there is need for more comprehensive studies on this subject, especially regarding the milk producing herds because of the possibility of transfer of the multidrug-resistant pathogens to animals and humans. This phenomenon is also important from an economic point of view. Thus, this study aims to: evaluate the resistance of Staphylococcus spp. isolated from clinical and subclinical bovine mastitis to the most commonly used antibiotics in clinical practice (beta-lactams and gentamycin), correlating the phenotype (in vitro susceptibility to antimicrobials) and genotype (detection and expression of genes coding for resistance) characteristics and also correlate these data with other virulence characteristics of the microorganisms, particularly those related to the presence of genes coding for adhesins and biofilms. Three hundred Staphylococcus isolates from milk samples will be characterized phenotypic and genotypically and submitted to in vitro susceptibility tests towards beta-lactam antibiotics and gentamycin; the minimal inhibitory concentration to oxacillin, penicillin, ampicillin, amoxicillin, cephalothin and gentamycin will be evaluated in CPS and CNS strains resistant to these antimicrobials. PCR will be used to evaluate for the presence of genes coding for adhesins (cna, eno, ebps, fib, fnbA, fnbB) and biofilms (icaA, icaB, icaC, icaD, bap, bhp); the occurrence and detection of the expression of genes associated with antimicrobial resistance - mecA, mecC, blaZ, femA, femB and aaca-aphD - using the PCR and RT-PCR will also be held. The information obtained can elucidate aspects about the micro-organisms profiles with regard to virulence factors, enabling new approaches to therapies and preventive measures, aiming at increasing productivity and quality of milk and minimizing losses to farmers. (AU)