Comprehensive analysis of antimicrobial resistance, biofilm formation and virulence factors of staphylococci isolated from bovine mastitis

Bovine mastitis, a prevalent disease, is often attributed to staphylococci species. These microorganisms can express a diverse array of virulence genes and have the capability to form biofilms, establishing a robust defense against antimicrobials and host immune responses. In this study, we analyzed 191 <i>Staphylococcus</i> spp.<i>,</i> of which 81 % were identified as <i>Staphylococcus aureus</i>, and 19 % as non-aureus staphylococci (NAS), including species such as <i>S. borealis, S. chromogenes, S. haemolyticus, S. saprophyticus, S. capitis, S. ratti,</i> and <i>S. pasteuri</i>. Our analysis involved determining antimicrobial susceptibility profiles, assessing biofilm-forming capacities, and identifying genes associated with virulence, biofilm formation, adhesion, and antimicrobial resistance. Notably, 17.2 % of the strains exhibited resistance to penicillin, with 97 % carrying the <i>blaZ</i> gene, while 9.4 % demonstrated resistance to erythromycin. All strains were sensitive to gentamicin and cefoxitin. Additionally, resistance was observed for clindamycin (8.4 %) and tetracycline (1.0 %). Concerning biofilm development, 2.6 % displayed no formation, 24.6 % were categorized as weak producers, 47.1 % as moderate, and 25.7 % as strong formers. Our investigation also unveiled the presence of virulence genes, such as superantigens like <i>sea</i> (4.7 %), <i>seb</i> (3.7 %), sec (8.4 %), <i>sed</i> (0.5 %), and <i>tst</i> (6.8 %); Panton-Valentine leukocidin (<i>pvl</i>) (59.7 %); haemolysins <i>hla</i> (88.5 %) and <i>hlb</i> (91.1 %); genes responsible for biofilm production <i>icaA</i> (87.9 %), <i>icaD</i> (78.5 %), and <i>bap</i> (4.2 %); and adhesion genes <i>fnbpA</i> (89.5 %), <i>fnbpB</i> (20.4 %), and <i>clfA</i> (89.0 %). Additionally, the strains were categorized into four groups based on their virulence attributes, revealing differences between <i>S</i>. <i>aureus</i> and NAS, with the latter showing a lower presence of the studied genes compared to <i>S. aureus</i> strains. This research sheds light on the resistance and virulence profiles of staphylococci strains associated with bovine mastitis, providing valuable insights for potential treatment approaches.