Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 20, 2001
Publication Date: December 31, 2001
Citation: Poole, T.L., Genovese, K.J., Anderson, T.J., Bischoff, K.M., Callaway, T.R., Nisbet, D.J. 2001. Inhibition of a vancomycin-resistant enterococcus by an anaerobic continuous-flow culture of chicken microflora. Microbial Ecology in Health and Disease. 13:246-253. Interpretive Summary: Microorganisms (particularly bacteria) that cause diseases in livestock and poultry are among the most serious problems our farmers face in keeping their animals healthy. Drugs that kill these microorganisms are called antibiotics and they are very important in animal production both in this country and throughout the world. One of the problems with antibiotic use is that, over time, certain disease-causing microorganisms adapt to the antibiotics such that it takes more and more of the drug to work effectively. This phenomenon is known as antibiotic resistance, and in some cases microorganisms can become so resistant that they can no longer be controlled effectively. Our research is focused on ways to circumvent the antibiotic resistance problem. We have discovered that certain harmless bacteria that grow normally in the gut of chickens are able to prevent the growth of, and even kill, a disease-causing bacteria known as Enterococcus faecium. This harmful bacteria is known to sometimes occur in meat products that we as consumers eat, and it can cause very serious cases of human food poisoning. Our work is important because it identifies a possible way to make our food supply safer from harmful microorganisms, it could help in reducing the amount of chemical antibiotics that farmers have to use, and it would certainly contribute to lessening the chance of harmful microorganisms becoming resistant to the antibiotics that are used.
Technical Abstract: During experiments to study horizontal transfer of vancomycin resistance among enterococci present in an anaerobic continuous-flow fermentation culture of chicken gastrointestinal microorganisms (CCF), bactericidal activity against ATCC # 700221 vancomycin resistant Enterococcus faecium (VRE) was observed. The experiments presented in this report were conducted to investigate bactericidal activity against VRE. When CCF was challenged with 10**7 CFU/ml VRE, the VRE population decreased to an undetectable level within 48 hours and could not be rescued by addition of vancomycin at 4ug/ml. In a reciprocal experiment, VRE at 10**8 CFU/ml, was challenged with 10**7 CFU/ml of CCF. 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 to 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 three strains of E. faecium isolated from chickens, four isolated from swine, and five obtained from the ATCC. No inhibition of Enterococcus spp. other than E. faecium was observed. The results of this study suggest that CCF may be an effective inhibitor of vancomycin resistant E. faecium.