Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2009
Publication Date: 9/16/2009
Citation: Poole, T.L., Byrd II, J.A., Callaway, T.R., Nisbet, D.J. 2009. Ecology of Enterococcus faecalis and niche-adapted or non-niche-adapted Enterococcus faecium in continuous-flow anaerobic cultures. Foodborne Pathogens and Disease. 6:901-906. Interpretive Summary: Bacteria must compete with each other in the environment in order to survive. Some bacterial strains produce antimicrobial compounds as a means to kill competing bacteria. One such bacterium is Enterococcus faecalis which produces a toxin that kills other bacterial cells including a closely related species, Enterococcus faecium. We have studied a mixed culture of chicken gastrointestinal bacteria that contains both of these species and have found that the Enterococcus faecium from this culture is resistant to the toxin produced by Enterococcus faecalis. The present study was done to understand the ecology that exists between the Enterococcus faecalis from the mixed culture and various strains of Enterococcus faecium because both of these bacterial species can cause fatal diseases in humans.
Technical Abstract: Objectives: To study the survivability of niche adapted Enterococcus faecium I.3rif (I.3rif) vs. non-niche adapted Enterococcus faecium (GRE47) in cultures that contain Enterococcus faecalis I.2. Methods: An anaerobic continuous-flow culture of chicken microflora (CCF) that models the chicken gastrointestinal tract was used for ecological survivability studies. Pure continuous-flow co-cultures were used to assess an inhibitory effect of E. faecalis I.2 on E. faecium isolates. Results: CCF eliminated GRE47 at a rate of 1.01 log10 cfu/mL/day; whereas, I.3rif survived in CCF at 4.5-6.5 log10 cfu/mL. In continuous-flow monocultures of GRE47 with an average concentration of 8.93 log10 cfu/mL, the addition of 100 mL (9.5% total volume) of CCF resulted in the displacement of GRE47 in approximately 14 days at a rate of 0.66 log10 cfu/mL/day. In continuous-flow co-cultures of E. faecalis I.2 and GRE47, GRE47 was eliminated from the culture at a rate of 1.24 log10 cfu/mL/day. In co-cultures of I.3rif and E. faecalis I.2, the I.3rif population fluctuated, but was at 6.86 log10 CFU/ml on day 21. Conclusions: A fit subset of the E. faecium I.3rif population was able to survive in CCF and in the presence of E. faecalis I.2 alone. No subset of the non-niche adapted E. faecium GRE47 was able to survive under the same conditions. Tolerance may be due to mutations or genes acquired by I.3rif during the initial colonisation of the chicken gastrointestinal tract. The mechanism by which E. faecium I.3rif is tolerant in CCF and in E. faecalis co-culture is currently unknown.