Ecology of Enterococcus faecalis and Niche-Adapted or Non-Niche-Adapted Enterococcus faecium in Continuous-Flow Anaerobic Cultures

Abstract

An anaerobic continuous-flow culture of chicken gastrointestinal microflora (CCF) and pure cultures of Enterococcus faecalis I.2 were used for survivability studies of niche-adapted and non-niche-adapted Enterococcus faecium isolates. CCF eliminated non-CCF niche-adapted glycopeptide-resistant E. faecium 47 (GRE47) at a rate of 1.01 log₁₀ cfu/mL/day, whereas CCF niche-adapted E. faecium I.3^rif survived in CCF at 4.5–6.5 log₁₀ cfu/mL. In continuous-flow monocultures of GRE47 (8.93 log₁₀ cfu/mL), the addition of 100 mL (9.5% total volume) of CCF resulted in the displacement of GRE47 in 14 days at a rate of 0.66 log₁₀ cfu/mL/day. Pure continuous-flow cocultures were used to assess a direct inhibitory effect of E. faecalis I.2 on E. faecium isolates. In cocultures of E. faecalis I.2 and GRE47, GRE47 was eliminated from the culture at a rate of 1.24 log₁₀ cfu/mL/day. In cocultures of E. faecalis I.2 and E. faecium I.3^rif, the E. faecium I.3^rif population fluctuated, but was 6.86 log₁₀ CFU/mL on day 21. A fit subset of the E. faecium I.3^rif population survived in CCF and with E. faecalis I.2 alone. No subset of the non-niche-adapted E. faecium GRE47 was able to survive under the same conditions. The mechanism by which E. faecium I.3^rif is tolerant in CCF, and in E. faecalis coculture is unknown. E. faecium I.3^rif and GRE47 possessed the cell wall adhesion factor efaAfm. E. faecalis I.2 was positive by polymerase chain reaction for gelE, efaAfs, cad, ccf, cdp, and cob, but not the cytolysin-associated gene cylMAB, suggesting that the mechanism of activity against E. faecium strains was due to factors other than the two-component cytolysin.