P05 | Risk profile of <i>Staphylococcus aureus</i> strains in raw milk cheeses: results of a preliminary survey along the supply chain

Purpose. Raw milk cheese can be contaminated with enterotoxin-producing strains of Staphylococcus aureus, posing potential risks to human health. Methods. In this preliminary investigation, two batches of raw milk cheese, produced in the same facility but with milk obtained from two distinct farms, were tested at different stages of the production process, up to the point of consumption. All isolates obtained were purified, and one isolate from each production phase, where available, was subjected to Whole Genome Sequencing. The reads were assembled using metaSPADES, genome typing was performed with MLST, and virulence genes (including enterotoxins) and antimicrobial resistance genes were detected using abritamr. Results. In the first batch analyzed, 6 strains of S. aureus were isolated from the aged cheese after 7 (n=3) and 45 days (n=3). In the second batch, 14 strains of S. aureus were isolated: in raw milk (n=5), in cheese aged for 7 days (n=3), 45 days (n=3), and 90 days (n=3). The sequencing analysis results showed that all samples contained clonal complex 97 (CC97), and CC5 strains were identified in some samples of aged cheese rind. Genes for resistance to fluoroquinolones and tetracyclines, mepA and tet(38), were identified in CC97 strains, while blaI, blaR1, and blaZ, which encode beta-lactamase resistance traits, were identified in CC5 strains. The selX gene, which encodes a virulence factor weaker than enterotoxins, was identified in all strains and both CCs, while the sea gene, which encodes enterotoxin A, was identified exclusively in CC5 strains. Conclusions. The results obtained highlight that S. aureus strains persist throughout the entire raw milk cheese production process, belong to different clonal complexes, and have distinct resistance and virulence profiles. Genomic analysis of risk factors provides essential information for assessing the danger of these isolates and guiding targeted control strategies to reduce contamination along the food chain and protect consumer health. The activities of this project were funded by the MASAF project, Supply Chain Agreement, Model Stable, Ministerial Decree No. 0673777 of 22/12/2021, V Notice No. 0182458 of 22/04/2022 and subsequent amendments.