Prevalence of virulence genes in Enterococcus species isolated from companion animals and livestock

Abstract

Enterococcus species have developed from being commensal bacteria to leading pathogens that cause infections in humans and animals. The gastrointestinal tract of mammals is the normal habitat of these species. Virulence factors are proteins that are produced by the bacterium which are used to enhance their pathogenicity. The objectives of this study were to isolate Enterococcus spp. from livestock and companion animals, differentiate between the different sub-species and detect the presence of important virulence genes. Rectal and saliva swabs were collected from dogs and cats, whereas only rectal swabs were collected from cattle and cloacal swabs from chickens. Presumptive Enterococcus was selected using Bile Esculin Azide (BEA) agar, and Enterococcus species were confirmed using the polymerase chain reaction (PCR) by amplifying the tuf gene. In order to differentiate between E. faecalis and E. faecium, a multiplex PCR was used to detect the SodA gene. The genes responsible for gelatinase production (gelE) and for conjugation (ccf) were also detected using PCR. Out of 211 animal swabs, 182 (86%) were positive for the tuf gene. Overall, there were 55 isolates of E. faecalis (30%) compared to 22 isolates of E. faecium (12%). The virulence genes had a prevalence of 52% and 36% for gelE and ccf, respectively, in all animal hosts. The results demonstrated that chicken cloacal samples had the highest prevalence for E. faecalis, gelE and ccf genes compared to all the other isolates detected from other animal hosts. The results also demonstrated a statistically significant (p < 0.05) association between the prevalence of virulence genes (gelE and ccf) and animal species from which Enterococcus spp. was isolated. We provided evidence that healthy livestock and companion animals can harbour pathogenic Enterococcus that can be transferred via the food chain as well as through close association such as petting and licking of humans. This study partially demonstrated that Enterococci spp. are capable of evolving from being simple commensal bacteria to becoming pathogens that cause infection in humans and animals through the acquisition of virulence factors through mobile genetic elements.