ARS | Publication request: Effect of Subtherapeutic Concentrations of Antibiotics on the Inhibitory Stringency of a Mixed Anaerobe Continuous-Flow Culture of Chicken Microflora Against Glycopeptide Resistant Enterococcus Faecium

Submitted to: National Foundation for Infectious Disease
Publication Type: Abstract
Publication Acceptance Date: June 24, 2003
Publication Date: N/A

Technical Abstract: Anaerobic gastrointestinal microflora play an important role in the health of food animals; however, the use of prophylactic antibiotic treatment may adversely affect the gut microflora predisposing animals to infection with enteropathogens. The purpose of this study was to determine the effects of certain antibiotics on the inhibitory stringency of a mixed anaerobic continuous-flow fermentation culture of chicken gastrointestinal microflora (CCF02). CCF02 cultures were treated with subtherapeutic concentrations of vancomycin, tylosin, or gentamicin. Twenty-four hours post-treatment with 10.0 or 40.0 ug/ml of each antibiotic, cultures were challenged with glycopeptide resistant Enterococcus faecium (GRE) at 10**6 CFU/ml. Untreated and vancomycin (10.0 ug/ml) treated CCF02 cleared GRE in 7 and 9 days at rates of 0.88 and 0.67 log10 CFU/ml, respectively. All other treatments allowed the persistence of GRE at 10**5-10**6 CFU/ml. Antibiotic treatments that reduced the inhibitory stringency of the CCF02 culture and allowed persistence of GRE had significantly decreased concentrations of acetic and propionic acids. Concentration changes of other volatile fatty acids did not correlate to clearance of GRE. Currently, the data suggests that species producing significant levels of acetic acid and/or propionic acid contribute to inhibition of GRE, and that low concentrations of antimicrobials may adversely affect the microbial ecology of the gut with respect to its ability to exclude exogenous bacteria. 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.