Exploring evolutionary perspectives and antibiogram analysis of biofilm-forming Staphylococcus aureus in goat mastitis.

Biofilm formation plays a key role in developing antimicrobial resistance in Staphylococcus aureus (S. aureus) and is thus a major virulence factor responsible for persistent intramammary infections and subclinical mastitis in goats. The current study investigated the prevalence and molecular characterization of biofilm-forming S. aureus isolated from goat mastitis, the associated risk factors, and comparative antibiogram profiling. A total of 768 milk samples were conveniently collected from farms dairy goats in three districts of Pakistan Multan, Bahawalpur, and Rahim Yar Khan. The results revealed a molecular prevalence (presence of nuc gene) of 206/426 (48.37%) for S. aureus in milk samples from goats. The risk factors analysis showed that age group, water availability, previous mastitis history, hygienic measures during milking, teat lesion, and veterinary services posed significant associations with S. aureus intramammary infections in goats. The prevalence of biofilm production by phenotypic methods i.e. Congo Red agar and Microtitre plate were recorded to be 36.90% and 27.67% respectively. In comparison, the genotypic confirmation was done by the presence of the icaA gene and was found to be 55.34%. The phylogenetic analysis of the icaA gene revealed high homology between sequences of study isolates and the isolates of other countries like India, Egypt, Japan Kenya, the USA, and China. The S. aureus subjected to the Kirby-Bauer disc diffusion method revealed the highest resistance to cefoxitin and oxytetracycline followed by gentamycin, amikacin, trimethoprim + sulphamethoxazole, and vancomycin. There was a slight variation among the resistant profile of biofilm and non-biofilm producing S. aureus strains against antimicrobial agents. Out of 206, 31.07% (64/206) tested isolates exhibited resistance to three or more antibiotics concurrently, categorizing them as multiple drug resistant (MDR) with multiple antibiotic resistance index greater than 0.2. The study concluded that biofilm-producing S. aureus is prevalent in dairy goats of different breeds, including Beetal, Teddi, Barbari, and Makhi-cheeni, across various lactation stages (early, mid, and late), regardless of milk collection times in Pakistan of Pakistan with risk to the udder health and milk quality. Moreover, the biofilm formation may be associated with multidrug resistance of study isolates.