Potential for Biofilm Formation and Antibiotic Resistance of Staphylococci Isolated from Bulk Tank Milk Samples

The prevalence of staphylococci in the environment of humans, including food, may lead to the production of toxins and food poisoning in consumers. Additionally, staphylococci constitute a reservoir of genes determining antibiotic resistance. The study aimed to compare the antibiotic resistance and biofilm-forming ability of staphylococci isolated from bulk tank milk and assess the occurrence of animal-associated methicillin-resistant Staphylococcus aureus. The study consisted of isolation of strains from cow milk, confirming their belonging to Staphylococcus sp. and S. aureus, investigation of the presence of a gene determining the production of coagulase, and genes determining resistance to beta-lactams, tetracyclines, vancomycin, natural penicillins, and aminopenicillins, as well as virulence genes determining biofilm production. There were 56 bacterial strains isolated, which belong to Staphylococcus spp. All isolates showed resistance to amoxicillin, erythromycin, and tetracycline. The lowest resistance was demonstrated for vancomycin (48.2%). The mecA gene was not detected in any of the isolates and there was no positive reaction to the PB2 protein, which indicates that none of the isolated strains was methicillin resistant. Only 26.8% of isolated strains did not show the ability to produce biofilm. Special attention should be paid to the health of dairy cows and the supervision of the use of antibiotics in the dairy herd environment because, even in milk from healthy cows, there is a real risk of the occurrence of multi-drug resistant bacteria.