Expression of genes encoding resistance in Staphylococcus spp. isolated from bovine subclinical mastitis in Brazil

Introduction: Staphylococci are the most important agents associated with bovine mastitis. This study aimed at characterizing resistance factors to antimicrobials in Staphylococcus spp. isolated from the milk of cows with subclinical mastitis. Methodology: In vitro resistance of 243 Staphylococcus spp. isolates to antimicrobials commonly used in clinical practice was evaluated. The detection and expression of genes encoding resistance mecA (gene encoding penicillin binding protein 2a) mecALGA251 (mecA homologue), blaZ (gene encoding penicillin resistance), femA and femB (genes encoding essential factors-A and B-for the expression of methicillin resistance) and aacA-aphD (gene encoding for a bifunctional enzyme that confers resistance to gentamicin) using PCR and RT-PCR was investigated. Results: One or more genes encoding resistance to different antimicrobials were detected in 184 Staphylococcus spp. samples. The femA and femB genes were the most frequent. Regarding the variables' detection (N = number of strains) and expression (% of strains), the following results were obtained: blaZ (N = 40-82.5%), femA (N = 147-47.6%), aacAaphD (N = 30-43.3%), femB (N = 138-29.7%), mecA (N = 33-27.3%), mecALGA251 (N = 01-0.0%). There was a higher occurrence of phenotypic resistant strains for amoxicillin, ampicillin and penicillin in isolates positive for detection and/or expression of blaZ gene when compared with the other genes. Conclusions: The present study provides new information on genotypic traits of Staphylococcus isolates from bovine subclinical mastitis especially regarding the evaluation of expression of genes associated with antimicrobial resistance in Staphylococcus spp. using molecular tools.