Occurrence of antibiotic resistance in environmental and amphibian E. coli isolates associated with cattle and aquatic environments

by 1978- Cissell, Robin Lynn

The widespread use of antibiotics in human medicine and livestock production has been linked to an increase in resistant bacteria, which may carry transferable resistance factors, including integrons. Foodborne pathogens, such as Escherichia coli and salmonella, commonly reside in livestock, including cattle, and these pathogens may acquire resistance genes as a result of routine antibiotic use. As cattle are often located in close proximity to aquatic environments, they may disperse antibiotic resistant pathogens into such environments, which may lead to contamination of aquatic wildlife. We hypothesize that class 1 integrons and/or antibiotic resistant bacteria occur more frequently in environments with cattle exposure, and resistance and class 1 integrons disperse into aquatic environments and wildlife, which in turn provides a reservoir of antibiotic resistant bacteria for cattle within that environment. We investigated the prevalence of resistance genes and class 1 integrons in E. coli from selected amphibian species from ponds within and adjacent to cow-calf beef production systems. Escherichia coli were isolated from bullfrog (Rana catesbeiana) and green frog (Rana clamitans) tadpoles, green frog metamorphs, cow manure, and pond water samples within each livestock system in an attempt to determine if transfer of resistant bacteria occurs. Integron prevalence within E. coli was determined by multi-plex PCR. Antibiotic resistance to tetracyclines, florfenicol, and sulfisoxazole were determined using standard microdilution broth Minimum Inhibitory Concentration technique. A selected subset of bacteria was analyzed for resistance patterns using the National Antimicrobial Resistance ii Monitoring System (N.A.R.M.S.). Class 1 integrons were detected in 3% of isolates (n = 63) from pond water and in 1% of isolates (n = 123) from cow manure. Integrons were not detected in isolates (n = 1014) from tadpoles or metamorphs. Tadpole samples with isolates resistant to tetracycline, florfenicol and sulfisoxazole were more prevalent (P=0.0001, P = 0.006 and P=0.0156 respectively) from cattle-accessible ponds compared to cattle-excluded ponds. The percentage of pond water samples with tetracycline resistant E. coli isolates was also greater in cattle-accessible ponds (P = 0.0283) compared to isolates from cattle-excluded ponds. Antimicrobial resistance patterns were observed to differ between treatments. Information from this study will provide key information for the development of strategies to reduce the prevalence and risk of antibiotic resistant organisms. Key words: Antibiotic resistance, Integron, E. coli, Salmonella, Amphibian iii Preface The terms antibiotic and antimicrobial are used interchangeably, and refer to compounds that kill or inhibit the growth of microorganisms. All figures and tables referred to in the text are located in the Appendix. iv