Detection of virulence and antimicrobial resistance genes in Staphylococcus aureus isolated from bovine mastitis in Brazil

Abstract

Staphylococcus aureus can present many mechanisms in order to remain in mammary gland. The present study aimed to evaluate virulence factors and genetic mechanisms of drug resistance in 400 S. aureus strains isolated from bovine mastitis in Brazil, as well as to assess the association between these characteristics, year of isolation and geographic origin of the strains. Singleplex and multiplex PCR was used to identify virulence factors and drug resistance encoding genes. Detection of biofilm-forming was carried out using Congo red Tryptic Soy Broth assay. As a result, 83.5% isolates were biofilm-forming and 98.5% strains exhibited the biofilm gene icaAD. Virulence genes luk (Panton–Valentine Leukocidin), seb (Staphylococcal Enterotoxin B), sec (Staphylococcal Enterotoxin C), sed (Staphylococcal Enterotoxin D), tst (Toxic shock syndrome toxin 1) were observed in 3.5%, 0.5%, 1%, 0.25% and 0.74% of the strains, respectively. Hemolysin genes were observed in 82.85% (hla + hlb + ), 16.5% (hla + ) and 0.75% (hlb + ) isolates. The gene blaZ, associated with penicillin resistance, was detected in 82.03% isolates, whereas tetracycline resistance gene tetK and aminoglycoside gene aac(6’)-Ie–aph(2’)-Ia were observed in 33.87% and 45.15%, respectively. Fluoroquinolone resistance gene mepA was detected for the first time in all fluoroquinolone resistance S. aureus isolates. Resistance genes tetM (3.22%), tetL (1.61%), ermA (14.29%), ermB (14.29%), ermC (33.3%), ermT (9.52%), ermY (4.76%), msrA (9.52%) and mphC (9.52%) were detected in low frequency among the isolates. Our results showed a high frequency of S. aureus carrying mainly biofilm and hemolysin genes. Moreover, a wide variety of antimicrobial resistance genes that confers resistance to all classes of antimicrobial agents used in animals and human population were observed. These results highlight the pathogenic potential of S. aureus from cattle to cause severe disease in both humans and animals.