Virulence factors, antimicrobials and heavy metals resistance in Enterococcus spp. isolates from food of animal origin

This study was aimed at investigating the presence of virulence factors, antimicrobial and heavy metals resistance in 97 isolated enterococci from food of animal origin. Phenotypic and genotypic tests for species-level identification of the recovered isolates were carried out. This resulted in the identification of 67 strains as Enterococcus faecium, 9 as Enterococcus faecalis, 3 as Enterococcus durans, 2 as Enterococcus hirae and 1 as Enterococcus raffinosus. In 15 isolates, their confirmation at species level was neither achieved by phenotypic nor by genotypic methods. Exopolysaccharides production was the most frequent virulence factor and was detected in 46 isolates, while 19 displayed gelatinase activity, and only one resulted beta-hemolytic. Minimum inhibitory concentration (MIC) study revealed that 29 isolates were vancomycin-resistant (>= 32 mu g/mL), 26 of them were also resistant to teicoplanin (>= 32 mu g/mL). On the other hand, of the total isolates, 21 exhibited resistance to tetracycline (>= 16 mu g/mL) and only 3 enterococci exhibited resistance to ampicillin (>= 16 mu g/mL). Agar plates test revealed that 90 strains were resistant to zinc (>= 12 mM) while all exhibited intermediate copper resistance (4-12 mM). Foods of animal origin act as a reservoir of Enterococcus spp. strains, expressing virulence factors, and resistance to antimicrobials and heavy metals. Therefore, the implementation of continuous surveillance in enterococci isolated from food of animal origin is essential to human health.