Prevalence and Virulence Characteristics of Enterococcus faecalis and Enterococcus faecium in Bovine Mastitis Milk Compared to Bovine Normal Raw Milk in South Korea

SIMPLE SUMMARY: Characterization of Enterococcus spp. among bovine mastitis pathogens is important in terms of the dairy industry and public health domain. The present study aimed to characterize virulence properties such as virulence genes (esp, asa1, gelE, and cylA), biofilm, gelatinase, hemolysis, and antimicrobial resistance and to compare them between bovine mastitis milk and bovine normal raw milk. Our results demonstrated that Enterococcus faecalis and Enterococcus faecium isolated from bovine mastitis milk exhibited higher virulence properties than those isolated from bovine normal raw milk. E. faecalis (90 isolates) was present at a significantly higher rate than E. faecium (32 isolates) and was more abundant in virulence genes. Furthermore, after analyzing the correlation between the virulence genes and the corresponding phenotype, we found that gelE and esp were involved in strong biofilm formation and the gelE was involved in gelatinase production. Taken together, E. faecalis in bovine mastitis milk should be monitored to control bovine mastitis and improve public health. ABSTRACT: Enterococcus spp. are pathogens that cause environmental mastitis and are difficult to eliminate owing to their resistance to antibiotics. To compare the virulence characteristics of isolates from bovine mastitis milk (BMM) and bovine normal raw milk (NRM), we isolated Enterococcus spp. from 39 dairy farms in South Korea from 2015–2020. A total of 122 Enterococcus spp. were identified, with Enterococcus faecalis (73.8%) accounting for the majority, followed by Enterococcus faecium (26.2%). E. faecalis isolated from BMM harbored gelE, asa1, esp, and cylA genes with a prevalence of 85.7, 71.4, 54.3, and 30.0%, respectively. These genes were significantly more abundant in BMM than in NRM, except for asa1 (p < 0.0001). Interestingly, strong biofilm and gelatinase formation was predominately observed for BMM isolates and this was significantly correlated to the presence of esp and gelE genes (p < 0.05). BMM isolates demonstrated higher resistance to tetracycline (59.3%), followed by chloramphenicol (21.0%), rifampicin (18.5%), doxycycline (4.9%), ciprofloxacin (1.2%), and nitrofurantoin (1.2%), than those from NRM. E. faecalis harboring esp, gelE, and cylA may be causative agents for bovine mastitis and act as a reservoir for the transmission of virulence factors to humans.