Enterococcus faecalis isolates of food origin and detection of their virulence determinant factors and genes in Osun State, Nigeria

Abstract

Resistance of Enterococcus faecalis to a wide variety of antibiotics has been severally reported. Antibiotic resistance only cannot explain the virulence of E. faecalis as an emerging pathogen of public health concern, causing a variety of human infections. In the present study, incidence of putative virulence determinants among E. faecalis strains isolated from different categories of food canteens namely; primary-school, fast-food and commoners’ canteens (bukataria) in Osun States, Nigeria was investigated. Six hundred and fifty-eight isolates were examined for the expressions of three putative virulence determinant factors; gelatinase, aggregation substance and cytolysin activator by phenotypic tests. Meanwhile, twenty selected representative strains were examined for virulence determinant genes; gelatinase (gelA), aggregation substance (asa 1), cytolysin activator (cylA), enterococcal surface protein (esp) and collagen-binding protein (ace) as well as confirmation of their identity by polymerase chain reaction (PCR). Six primers were used to amplify the DNA from all the 20 selected E. faecalis strains examined. Expression of putative virulence determinant factors (gelatinase, cytolysin activator and aggregation substance) in all the isolates was low (10.18, 13.83 and 29.03%, respectively). The percentage of isolates with GelA, cylA and asa1 genes (95, 15 and 75%) was higher compared to the isolates that show phenotypic expression (40, 15 and 30%, respectively) of the virulence determinants. None of the isolates had less than two out of the five virulence determinants investigated while, the highest was four in 1 (13%) and 4 (57%) of primary school canteen and bukataria isolates respectively. Moreover, statistically there is no significant association (p < 0.05) between the virulence markers and canteen sources. It is concluded that, potentially virulent E. faecalis occurred in environment of a number of canteens in Osun State, Nigeria, which may hide phenotypic expression. Hence, there is need for constant epidemiological surveillance and strict enforcement of good hygiene practices.

Keywords: Virulence determinants, Enterococcus faecalis, phenotypic expression, food canteens, gelatinase, cytolysin activator, aggregation substance.