Antimicrobial Activity, Antibiotic Resistance and the Safety of Lactic Acid Bacteria in Raw Milk <scp>V</scp>altellina <scp>C</scp>asera Cheese

Abstract

Abstract The study involved 75 autochthonous lactic acid bacteria ( LAB ) obtained from V altellina C asera Protected Designation of Origin 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 S treptococcus thermophilus was predominant, while E nterococcus and the L actobacillus casei group prevailed in ripened cheese. One L actobacillus rhamnosus was resistant to penicillin G . The presence of 19 tetracycline‐resistant strains indicates that tetracycline resistance is emerging in dairy sources. Seven E nterococcus faecalis , one L actococcus garvieae and one Lactoc . lactis subsp. lactis showed the presence of the int gene that is responsible for the transfer of tetracycline resistance. Six En . faecalis inhibited L isteria monocytogenes and closely related LAB , and four of these harbored the ent AS48 gene. Genes associated with virulence factors were detected in En . faecalis but not in En . faecium . A low spread of AR in wild LAB and a low occurrence of safety hazards in enterococci strains were highlighted. Practical Application In recent years, raw milk cheese have received increasing attention for their microbial biodiversity and as a source of food bio‐preservatives, but they could also provide a vehicle for antibiotic resistance. The results of this study showed that wild microbiota of V altellina C asera cheese is characterized by an important activity inhibiting growth of L isteria monocytogenes. These probably actively contribute to ensure the safety and quality of this cheese. The presence of tetracycline resistance among En . faecalis and Str . thermophilus may indicate that this resistance is emergent in dairy sources, a point that needs further investigation. En . faecium from artisanal V altellina C asera cheese did not show antibiotic resistance and did not harbor any of the virulence genes associated to the hospital‐associated clade according to European Food Safety Authority.