Virulence factors, antibiotic resistance, and bacteriocins in enterococci from artisan foods of animal origin

Abstract

A collection of 25 isolates from foods of animal origin (including mainly milk and cheese, together with meat and ham) was studied. Enterococci were identified at species levels as E. faecalis (9 isolates) and E. faecium (16 isolates). Investigation of virulence factors by PCR amplification revealed incomplete sets of cytolysin genes both in E. faecalis and E. faecium isolates. Among E. faecalis, PCR amplification revealed a high incidence of genes encoding for enterococcal surface protein esp (7/9 isolates), enterococcal antigen efaA fs (6/9), aggregation substance agg (2/9) and sex-pheromone encoding genes ccf, cob, cpd (which were detected in 9, 5 and 3 out of 9 isolates, respectively). By contrast, only esp (7/16 isolates) and efaA fm (10/16) were detected among E. faecium. Antibiotic resistance detected at higher frequencies included rifampicin, nitrofurantoin, ciprofloxacin and levofloxacin. Vancomycin resistance was also detected among E. faecalis and E. faecium. E. faecalis isolates showed decarboxylating activity mostly for tyrosine (5/9 isolates), while E. faecium isolates showed a broader decarboxylating capacity, involving tyrosine (11/16 isolates) ornithine (6/16), lysine (4/16) and histidine (3/16). Six isolates produced bacteriocins, and genes encoding for enterocins A, B, P, L50, and 1071 were detected. Many isolates tested positive for several of the traits investigated, which raises concerns about their possible role as reservoirs for dissemination of antibiotic resistance and virulence traits in foods.