Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2004
Publication Date: 6/15/2004
Citation: Poole, T.L., Genovese, K.J., Callaway, T.R., Bischoff, K.M., Donskey, C.J., Nisbet, D.J. 2004. Competitive exclusion of a glycopeptide resistant Enterococcus faecium GRE in the presence of vancomycin, but not equivalent concentrations of tylosin or gentamicin. Poultry Science. 83:1099-1105.
Interpretive Summary: Antibiotics have different activities against different species of bacteria. Many of the bacteria that live in the gut of animals and man cannot live in regular air; these bacteria are called anaerobes. Some anaerobes are believed to be beneficial to animal health by preventing disease causing bacteria from infecting animals and people. Broad spectrum antibiotics kill many species of bacteria; while, narrow-spectrum antibiotics only kill a few species. This study was done to assess the effect of different antibiotics on the ability of good bacteria to prevent disease causing bacteria from becoming established in a laboratory model of the gut. The results indicate that both broad spectrum and narrow spectrum antibiotics may adversely effect the protective nature of good bacteria. Verification of these results in live animals is necessary to determine if antibiotics may compromise the ability of gut bacteria to serve as a defense against infectious disease.
Technical Abstract: The effect of subtherapeutic concentrations of antibiotics (10.0 and 40.0ug/ml vancomycin, gentamicin, and tylosin) on the efficacy of a competitive exclusion culture was studied in a continuous-flow fermentation system. Efficacy of a mixed anaerobe culture of chicken microflora (CCF) following antibiotic treatment was assessed by challenge with glycopeptide resistant Enterococcus faecium (GRE) at 6.0 log10 cfu/ml. Bacterial enumeration of endogenous CCF isolates, volatile fatty acid (VFA) analysis, and challenge with GRE indicated that CCF efficacy was affected by all antibiotic treatments. Although treatment of CCF with 10.0ug/ml vancomycin eliminated GRE at a rate of 0.61 log10 cfu/ml/day, it was unable to eliminate E. coli, a Gram negative challenge organism. All other antibiotic treatments allowed the persistence of GRE between approximately 2.0 and 6.5 log10 cfu/ml. All antibiotic treated cultures had decreased concentrations of acetic and propionic acids. Our data suggest that low concentrations of antimicrobials may adversely affect the microbial ecology of gut microflora with respect to its ability to exclude exogenous bacteria. Moreover, gentamicin had an adverse effect on the inhibitory stringency of CCF even though it showed little activity against strict anaerobes from CCF in pure culture. Verification of the results 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.