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 Staphylococcus spp., of which 81 % were identified as Staphylococcus aureus, and 19 % as non-aureus staphylococci (NAS), including species such as S. borealis, S. chromogenes, S. haemolyticus, S. saprophyticus, S. capitis, S. ratti, and S. pasteuri. 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 blaZ 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 sea (4.7 %), seb (3.7 %), sec (8.4 %), sed (0.5 %), and tst (6.8 %); Panton-Valentine leukocidin (pvl) (59.7 %); haemolysins hla (88.5 %) and hlb (91.1 %); genes responsible for biofilm production icaA (87.9 %), icaD (78.5 %), and bap (4.2 %); and adhesion genes fnbpA (89.5 %), fnbpB (20.4 %), and clfA (89.0 %). Additionally, the strains were categorized into four groups based on their virulence attributes, revealing differences between S. aureus and NAS, with the latter showing a lower presence of the studied genes compared to S. aureus 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.