Ecology of Enterococcus faecalis and niche-adapted or non-niche-adapted Enterococcus faecium in continuous-flow anaerobic cultures.

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 log(10) cfu/mL/day, whereas CCF niche-adapted E. faecium I.3(rif) survived in CCF at 4.5-6.5 log(10) cfu/mL. In continuous-flow monocultures of GRE47 (8.93 log(10) 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 log(10) 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 log(10) 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 log(10) 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.