Low Occurrence of Virulence Determinants in Vancomycin-Resistant Enterococcus from Clinical Samples in Southwest Nigeria

Background: The virulence factors of enterococci play a major role in the pathogenicity of enterococcal strains. Objectives: This study aimed to evaluate virulence factors and detect selected virulence and resistance genes in vancomycin-resistant Enterococcus (VRE) from clinical samples from southwest Nigeria. Methods: The VRE isolates (n = 85) recovered from clinical samples were characterized using conventional microbiology techniques, and molecular identification was made with ddlE primers. Phenotypic screening for five virulence determinants and detection of virulence and resistance genes using a polymerase chain reaction were carried out. Results: Phenotypic identification revealed 61 Enterococcus faecium and 24 Enterococcus faecalis. All the isolates hydrolyzed bile. Moreover, 88.2% of the isolates produced biofilm; however, 72.9% of the isolates produced gelatinase enzyme. Altogether, six isolates (7%) produced all five virulence factors. The least virulence factor expressed by the two species E. faecium and E. faecalis was DNase at 21.3% and 29.2% followed by cytolysin at 27.9% and 41.7%, respectively. Only 25 isolates (29.4%), including 23 E. faecium (37.7%) and only 2 (8.3%) E. faecalis isolates, revealed bands with molecular identification. Additionally, VRE isolates showed bands for asa1 (16%); only 1 (4%) isolate had the hyl gene and vanB gene, respectively. Conclusions: The absence of vanA and low detection of vanB resistance genes suggest the possible presence of other van types and emphasizes the need for further investigations on the incidence of other van genes using molecular screening methods in enterococci isolates in Nigeria for surveillance purposes. Moreover, the low occurrence of virulence genes implies that there might be other mediators of pathogenicity involved in Enterococcus virulence traits.