Enterococcus faecalis and E. faecium in Dairy Production Line: Antibiotic Resistance Profile and Virulence Characteristics

This study investigated the prevalence, antimicrobial resistance and virulence of Enterococcus faecalis and E. faecium , in two dairy plants, posing public health risks. Overall, from 219 samples, 42 were contaminated with E. faecium (26/42, 62%) or E. faecalis (16/42, 38%), which confirmed via PCR and BD Phoenix automated system. Antibiotic resistance was found in 48% of the enterococci isolates, with high rates for azithromycin (31% E. faecalis, 27% E. faecium ), erythromycin (44% E. faecalis, 27% E. faecium ), and tetracycline (19% E. faecalis, 12% E. faecium ). ciprofloxacin and vancomycin resistances were rare (below 10% for both). Notably, 25% of the resistant isolates were multidrug-resistant (MDR) with a Multiple Antibiotic Resistance (MAR) index of 0.3. Virulence analysis showed that 69% of 42 isolates harboured at least one esp or efaA, or both genes which are essential for enterococcal pathogenesis, while 67% of isolates produced biofilms. Most antibiotic-resistant isolates (60%) were biofilm producers and harboured associated virulence genes. In conclusion, antibiotic-resistant E. faecalis and E. faecium along the dairy production line might pose potential food safety and public health concerns, due to their presence in biofilm communities, which enhance antibiotic resistance and facilitate horizontal gene transfer.