Co-Occurrence of Biofilm Formation and Disinfectant-Antimicrobial Resistance in Staphylococcus spp. Along the Dairy...

This study aims to investigate the co-occurrence of biofilm formation and resistance to disinfectants and antimicrobial agents in Staphylococcus spp. isolated from different stages of the dairy production chain, and to assess the contribution of these traits to persistence in dairy processing environments. A total of 51 Staphylococcus isolates, including coagulase-positive and coagulase-negative species, were recovered from raw milk, dairy products, and food-contact surfaces after disinfection. Biofilm and slime formation were assessed phenotypically, while biofilm-associated (icaA, icaD, bap) and disinfectant resistance-associated genes [qac (A, B, C, G, H, J), mdeA, lmrS, and norA] were detected by PCR. Antimicrobial susceptibility was determined by disk diffusion, and disinfectant resistance by broth microdilution. Biofilm and/or slime formation was detected in 52.9% of isolates, including 89% of Staphylococcus aureus and 45.2% of coagulase-negative staphylococci. Resistance to oxacillin was highly prevalent (94.1%), followed by tetracycline (29.4%) and erythromycin (17.6%). Reduced susceptibility was most frequently observed for quaternary ammonium compound-based disinfectants (62.7%), whereas resistance to phosphate-acid-, chlorine-, and peracetic acid-based disinfectants ranged from 17.7% to 35.3%. According to the study results, Staphylococcus species combine biofilm-forming capacity with decreased susceptibility to commonly used disinfectants and high levels of antimicrobial resistance, with oxacillin and QACs resistance being particularly prevalent. Overall, the findings highlight the presence of resistant staphylococci in the dairy production chain and underscore the need for optimized hygiene and control strategies.