Abstract
During experiments to study the horizontal transfer of vancomycin resistance among enterococci present in an anaerobic continuous-flow fermentation (CCF) culture of chicken gastrointestinal microorganisms, inhibitory activity against an exogenous vancomycin-resistant Enterococcus faecium (VRE) was observed. The experiments presented in this report were conducted to investigate the inhibitory activity against VRE 700221. When CCF was challenged with 10 7 CFU/ml VRE, the VRE population decreased to an undetectable level after 48 h and could not be rescued by addition of vancomycin at 4 µ g/ml. In additional continuous ow experiments with vancomycin-resistant E. faecium A256, macrolide and streptogramin-resistant E. faecium 3167 and vancomycin-resistant E. faecalis 700802, clearance was observed in approximately 4 days. In a reciprocal experiment, VRE at 10 8 CFU/ml was challenged with 10 7 CFU/ml CCF culture. CCF displaced VRE by 15 days in all replicate experiments. When CCF and VRE were simultaneously inoculated with 10 7 CFU/ml, VRE was undetectable in 7 days. Prophylactic treatment of day-old broiler chicks with CCF prevented VRE cecal colonization after VRE challenge as compared with the untreated controls. In four replicate experiments, VRE colonization occurred in less than 5% of chicks that were inoculated with CCF prior to challenge with VRE. A bacteriocin agar overlay assay identified three E. faecalis isolates from CCF that exhibited inhibitory properties toward all E. faecium tested; this included two strains of E. faecium isolated from chickens, four isolated from swine and four obtained from the ATCC. No inhibition of Enterococcus spp. other than E. faecium was observed. The results of this study may suggest an amensalistic relationship among different enterococci populations. Keywords: Vancomycin-resistant enterococci, competitive exclusion, chicken gastrointestinal microorganisms.
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