Dissemination of vancomycin-resistant enterococci harboring vanA through disposal of waste derived from industrial production of vancomycin

We demonstrated the occurrence of vancomycin-resistant enterococci (VRE) in waste derived from the industrial production of vancomycin and their dissemination through disposal of such waste into a sewage treatment plant. Bacteriological counts on a medium selective for enterococci (Slanetz-Bartley agar) revealed the presence of high numbers of presumptive VRE (approximately 106 CFU/ml) in the waste originating from the fermentation biomass used for vancomycin production. The waste was also found to contain active residues of vancomycin (64-1, 024 μg/ml) by bioassays using a vancomycin-susceptible enterococcal strain. Randomly amplified polymorphic DNA (RAPD) analysis of 65 presumptive VRE isolates from the waste allowed distinction of four genotypes, two of which (A and D) belonged to the genus Enterococcus, most likely E. faecium, and harbored the vanA gene conferring high-level vancomycin resistance. The same VRE strains found in the waste occurred also in the biological tanks and the final effluent of the sewage treatment plant receiving the waste, as demonstrated by the detection of undistinguishable pulsed-field gel electrophoresis (PFGE) patterns in VRE isolated from these sources. These results indicate the need to assess the possible dissemination of VRE and other antibiotic-resistant bacteria through disposal of waste derived from antibiotic production.