Submitted to: Microbial Drug Resistance
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 14, 2001
Publication Date: December 1, 2001
Citation: POOLE, T.L., HUME, M.E., GENOVESE, K.J., ANDERSON, T.J., SHEFFIELD, C.L., BISCHOFF, K.M., NISBET, D.J. PERSISTANCE OF A VANCOMYCIN-RESISTANT ENTEROCOCCUS FAECIUM IN AN ANAEROBIC CONTINUOUS-FLOW CULTURE OF PORCINE MICROFLORA IN THE PRESENCE OF SUBTHERAPEUTIC CONCENTRATIONS OF VANCOMYCIN. Microbial Drug Resistance. 2001. Interpretive Summary: It is believed, by some, that the use of antibiotics in medicated animal feed may cause an increase of antibiotic resistant bacteria in the intestines of animals. There is a concern that these resistant bacteria will transfer resistance determinants to disease causing bacteria, such as Enterococci, that may be transferred to humans via the food supply. This study used a mixed culture of bacteria from the intestine of a pig to study gene transfer between members of the bacterial genus, Enterococcus. Vancomycin Resistant Enterococcus (VRE) was added in the presence and absence of sub-therapeutic levels of vancomycin to determine the effect the antibiotic might have on gene transfer. Although VRE is generally cleared from the mixed culture within 7 days, the addition of subtherapeutic vancomycin allowed VRE to persist for up to 24 days. Vancomycin resistance gene transfer from VRE to other Enterococcus present in the mixed culture was not detected at any time throughout the experiments. This suggests that under the experimental conditions used in this study, vancomycin resistance gene transfer is a rare event.
Technical Abstract: Recombined porcine continuous-flow culture (RPCF) maintained in a continuous-flow fermentation system is effective in protecting neonatal and weaned pigs against infection by enteropathogens. A similar chicken continuous-flow culture with endogenous enterococcus is bactericidal against vancomycin-resistant Enterococcus faecium (VRE). In the current study we demonstrate the effect of RPCF on VRE in the presence and absence of subtherapeutic levels of vancomycin. Also examined was the ability of the VRE to transfer vancomycin resistance to E. faecalis 137.1, which is endogenous to RPCF. When RPCF was challenged with VRE the rate of clearance of the VRE was dependent on the method of challenge. In the control experiment, RPCF was challenged with 10**7 CFU/ml VRE and VRE was cleared from the culture within 7 days. RPCF containing 0.001ug/ml vancomycin cleared VRE at a similar rate. In contrast, RPCF containing 0.01ug/ml or 0.1ug/ml vancomycin reduced the level of VRE from 10**7 CFU/ml to 10**2 CFU/ml within 9 days, but failed to clear the VRE after 24 days. E. faecalis 137.1 endogenous to RPCF did not acquire the vancomycin resistance genes throughout the experiment as evidenced by direct selection, ribotyping and pulse-field gel electrophoresis.