Antibiotic resistance in piedmontese and ligurian dairy production

Background The dissemination of antibiotic resistance genes (ARGs) through the food chain represents a major threat to public health. Dairy products from raw milk containing lactic acid bacteria (LAB) resistant to antimicrobials may serve as vectors for the transfer of resistance to commensal or potentially pathogenic bacteria in the human gut. Objectives This study aimed to investigate the presence of ARGs in dairy products and milk and assess the antibiotic susceptibility of LAB strains isolated from diary products made from raw milk. Methods 41 dairy products (21 cheeses, 16 milks and 4 curds) were analysed. Antimicrobial residues were assessed using Delvotest, lateral flow rapid tests, and LC-HRMS. The presence of resistance genes related to tetracyclines, β-lactams, quinolones and erythromycin was examined using six multiplex PCR assays. The isolated LAB strains were identified by MALDI-TOF and subsequently evaluated for antibiotic resistance through the detection of the resistance genes described above, as well as by phenotypic methods, including the Kirby-Bauer disk diffusion test and determination of the minimum inhibitory concentration (MIC) for the main classes of antibiotics employed in both medical and veterinary practice. Results All dairy samples tested for antibiotic residues were within legal limits. ARGs were detected in all food matrices, most frequently against tetracyclines (96%), erythromycin (66%), β-lactams (55%), and quinolones (38%). Among isolated LAB strains, 20 out of 58 (34.5%) harbored at least one ARG, predominantly tetracycline resistance genes (80%), followed by β-lactams (25%), erythromycin (20%), and quinolones (5%). Conclusions This study confirmed that LAB present in dairy products can function as reservoirs of ARGs, representing a potential source for horizontal gene transfer within microbial ecosystems in foods and, ultimately, in the human gut. The results emphasize the importance of continuous monitoring of antimicrobial resistance in LAB and the implementation of preventive measures to limit the dissemination of resistance through dairy production and consumption.