MONITORING ANTIBIOTIC RESISTANCE IN BIOLOGICAL WASTE TREATMENT SYSTEMS

Two anaerobic sequencing batch reactor (ASBR) systems were operated for one year to treat swine waste containing the antimicrobial compound tylosin at an average concentration of 1.6 mg liter−1. Tylosin (a macrolide antibiotic) was used as a feed additive at the facility from which swine waste was obtained. Tylosin levels in ASBR biomass and effluent were always below the detection limit (0.26 mg liter−1), indicating that tylosin was degraded in the ASBRs. Using oligonucleotide hybridization probes, we observed a rapid increase in levels of macrolide, lincosamide, and streptogramin of the B type (MLSB)-resistant Bacteria during startup of the ASBRs due to introduction of MLSB-resistant strains present in the swine waste, gene transfer, and/or a shift in the microbial community structure. After startup, the level of MLSB-resistant Bacteria in ASBR biomass fluctuated around approximately 40% (as a percentage of the total 16S ribosomal RNA), whereas the level of MLSB-resistant Bacteria in swine waste averaged 22.4%. It was also determined that the levels of MLSB-resistant Bacteria in samples from a variety of waste treatment systems environments with no or limited exposure to tylosin or other antimicrobials were generally much lower than those in the swine waste containing tylosin and in the ASBRs treating this swine waste.