Antimicrobial activity, antibiotic resistance, and the safety of lactic acid bacteria in raw milk Valtellina Casera cheese

The study involved 75 autochthonous lactic acid bacteria (LAB) obtained from Valtellina Casera PDO cheese, and provides data on their antibiotic resistance (AR), antimicrobial activity and safety aspects. High biodiversity was revealed, assigning the isolates to 16 species. In the curd Streptococcus thermophilus was predominant, while Enterococcus and the Lactobacillus casei group prevailed in ripened cheese. One Lactobacillus rhamnosus was resistant to penicillin G. The presence of nineteen tetracycline resistant strains indicate that tetracycline resistance is emerging in dairy sources. Seven Enterococcus faecalis, 1 Lactococcus garvieae, and 1 L. lactis subsp. lactis showed the presence of the int gene that is responsible for the transfer of tetracycline resistance. Six E. faecalis inhibited Listeria monocytogenes and closely related LAB, and 4 of these harboured the entAS48 gene. Genes associated with virulence factors were detected in E. faecalis but not in E. faecium. A low spread of antibiotic resistance in wild LAB and a low occurrence of safety hazards in enterococci strains were highlighted.