Enterococcus spp. from Azeitao and Nisa PDO-cheeses: Surveillance for antimicrobial drug resistance

Enterococcus spp. were isolated from PDO-cheese of Azeita similar to o and Nisa at six cheesemaking units (Azeita similar to o: A1, A2, A3, A4; and Nisa: N9, N10), over four years (2016-2019). Genomic typing was performed using RAPD and distinct enterococci (n = 145) were identified at the species level by multiplex-PCR and evaluated regarding antimicrobial drug resistance (AMR). Antibiotics from nine distinct classes (aminoglycosides, macrolides, oxazolidinones, chloramphenicol, streptogramins, tetracyclines, glycopeptides, 13-lactams, and quinolones) were selected for AMR surveillance and breakpoint criteria defined by EUCAST and CLSI were considered and compared. Regarding species allocation, 78 enterococci were identified as E. faecium, 37 confirmed as E. faecalis and 30 as E. durans. High levels of resistance to quinupristin-dalfopristin, tetracycline and teicoplanin were observed. Some resistances to clinically relevant antimicrobials were also detected, including 13-lactams, aminoglycosides, and glycopeptides. Two isolates were considered multidrug-resistant, one according to EUCAST and the other to CLSI breakpoint criteria. Overall, considering the absence of reports regarding enterococcalrelated toxinfections or infections resulting from the consumption of PDO-cheeses, traditional foods harbouring these bacteria should be considered safe. However, the possibility of horizontal gene transfer events associated with antibiotic resistance determinants further highlights the importance for AMR surveillance along the food chain.

Automated summary

Enterococcus spp. were isolated from PDO-cheese of Azeita and Nisa, showing high levels of resistance to multiple classes of antibiotics. Some isolates were considered multidrug-resistant. Further surveillance for antimicrobial drug resistance is important to prevent potential risks associated with horizontal gene transfer events.