Submitted to: American Society for Microbiology Conference
Publication Type: Abstract Only
Publication Acceptance Date: February 15, 2005
Publication Date: August 28, 2005
Citation: Poole, T.L., Nisbet, D.J. 2005. Anatagonistic interactions between E. faecalis and E. faecium in a mixed anaerobic continuous-flow culture of chicken cecal microflora [abstract]. American Society for Microbiology. p. 50. Technical Abstract: An anaerobic continuous-flow culture of chicken cecal microflora (CCF) and Glycopeptide Resistant Enterococcus faecium (GREF) were used as a model to study the complex microbial ecology of the gastrointestinal reservoir. CCF competitively excludes exogenous GREF in approximately 7 days, and after 10 days GREF cannot be rescued by treatment with 100 ug/ml vancomycin. This study examined the efficacy of CCF after treatment with the antibiotics: vancomycin, gentamicin and tylosin (10 and 40 ug/ml each). These drugs differentially affect the strict anaerobes in CCF. Tylosin and gentamicin have the greatest and least effect on the anaerobes in CCF, respectively. The efficacy of CCF post-treatment was assessed by bacterial enumeration of selected CCF anaerobes, volatile fatty acid (VFA) concentrations and challenge with GREF at 6.0 log10 CFU/ml. Treatment with all antibiotics affected the efficacy of CCF as a competitive exclusion culture. Interestingly, CCF treated with 10.0 ul/ml vancomycin was still able to eliminate GREF at a rate of 0.61 log10 CFU/ml per day, but was unable to eliminate E. coli; thus demonstrating an inhibitory specificity to E. faecium. Four species of enterococci, E. faecium I.3, E. faecalis I.2, E. avium I.6 and E. gallinarum I.5 are present in CCF. E. faecalis is the predominant species present at concentration of 6.0-7.0 log10 CFU/ml. Treatment with 40.0 ul/ml vancomycin eliminated all endogenous enterococci in CCF; whereas, treatment with 10.0 ul/ml vancomycin did not eliminate E. faecalis I.2. E. faecalis I.2 has been previously shown to produce a bacteriocin-like activity against exogenous E. faecium isolates from poultry swine and humans. To further investigate the inhibitory specificity of E. faecalis I.2 against E. faecium continuous-flow co-cultures of E. faecalis I.2 and GREF were examined. E. faecalis I.2 maintained a concentration of 7.0-7.5 log10 CFU/ml over 14 days; whereas, GREF was eliminated from the culture at a rate of 1.01 log10 CFU/ml per day. By day 12 GREF was below detection levels. The ability of the endogenous E. faecium I.3 to survive at low levels in CCF may be due to immunity factors acquired during the initial colonization of the gastrointestinal tract. A process sometimes referred to as niche adaptation. Verification of the results of this study in live animals will be necessary to determine if antimicrobial treatment could compromise the effectiveness of normal microflora to serve as a natural host defense against infection.