Progress 03/01/04 to 06/30/06
Outputs
During this project, we sampled 248 cattle on 4 dairies. Each dairy was visited 9 times at 3-month intervals, and therefore, some of the individual cattle have been sampled over 9 consecutive visits. We recorded antibiotic usage information for each of these animals as well as for each herd. In addition, all morbidity in the herd was recorded, including any clinical mastitis. We tested all of the bacteria in our collection, which included over 15,000 isolates of E. coli, Enterococcus and Bacteroides / Prevotella for their resistance profiles. In general, we observed decreased susceptibility to specific antibiotics in the bacterial isolates from the younger animals. The older animals typically possessed completely sensitive bacterial strains in their feces. In addition, the bacterial isolates that we recovered from subclinical and clinical mastitis infections tended to be pan-susceptible. We detected and described a genetic linkage in E. coli among genes conferring
resistance to tetracycline, florfenicol and ceftiofur. Our data will help explain the ecological complexities of resistance gene dynamics on dairy farms.
Impacts
This study aims to determine the relationship between bacteria that cause disease (pathogens) and those that do not (commensals) in animals as it pertains to antibiotic resistance. Specifically, we hypothesized that this type of reservoir would explain the apparent persistence of antibiotic resistance genes, even after antibiotic use has ceased.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
During this project, we sampled 248 cattle on 4 dairies. Each dairy was visited 9 times at 3-month intervals, and therefore, some of the individual cattle have been sampled over 9 consecutive visits. We recorded antibiotic usage information for each of these animals as well as for each herd. In addition, all morbidity in the herd was recorded, including any clinical mastitis. We tested all of the bacteria in our collection, which included over 15,000 isolates of E. coli, Enterococcus and Bacteroides / Prevotella for their resistance profiles. In general, we observed decreased susceptibility to specific antibiotics in the bacterial isolates from the younger animals. The older animals typically possessed completely sensitive bacterial strains in their feces. In addition, the bacterial isolates that we recovered from subclinical and clinical mastitis infections tended to be pan-susceptible. We detected and described a genetic linkage in E. coli among genes conferring
resistance to tetracycline, florfenicol and ceftiofur. Our data will help explain the ecological complexities of resistance gene dynamics on dairy farms.
Impacts
This study aims to determine the relationship between bacteria that cause disease (pathogens) and those that do not (commensals) in animals as it pertains to antibiotic resistance. Specifically, we hypothesized that this type of reservoir would explain the apparent persistence of antibiotic resistance genes, even after antibiotic use has ceased.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
During this project, we have sampled 224 cattle on 4 dairies. Each dairy has been visited 8 times, and therefore, some of the individual cattle have been sampled over 8 consecutive visits. We have recorded antibiotic usage information for each of these animals as well as for each herd. In addition, all morbidity in the herd has been recorded, including any clinical mastitis. We hypothesized that individual animals that had been treated with antimicrobials would possess a higher proportion of antimicrobial resistant E. coli in their feces, and that these resistant E. coli would persist in the animal over time. We also hypothesized that changes in the resistance levels in the E. coli of one animal would influence the E. coli populations of other animals in the same age cohort. The minimum inhibitory concentration (MIC) to various antimicrobials was determined for 3 to 6 randomly selected E. coli colonies from each sample. The main factor associated with increased
resistance levels was age. Young calves had a greater diversity of E. coli MIC phenotypes, and many of these E. coli isolates had elevated MICs to multiple antibiotics. However, regardless of treatment history, the animals had E. coli with lower MIC levels after 6 to 9 months of age. Other animals in the same age cohort had similar MIC patterns. Preliminary results show that individual animal antibiotic treatments are not highly selective for resistant phenotypes over extended periods of time. We have optimized two different multiplex PCR protocols for the detection of specific antibiotic resistance genes. One protocol detects the resistance gene flo, which confers resistance against florfenicol, and the gene cmlA, which confers resistance against chloramphenicol. To date, we have found 42 of 611 (6.9%) of the E. coli from feces with the flo gene, and only 3 of 611 with the cmlA gene. These genes are likely on plasmids, and we are currently determining their precise location within
the bacterium. The E. coli in which these genes were detected are of different DNA fingerprint patterns suggesting that the gene has been transferred to multiple E. coli types. The other PCR we have optimized detects the cmy-2 and the cmy-1 gene families, which both confer resistance against third-generation cephalosporins. The cmy-2 gene has been detected in 13 of 562 (2.3%) E. coli tested to date, but we have not detected the cmy-1 gene family. Again, the E. coli that possess the cmy-2 gene are of differing DNA fingerprints suggesting the transfer of this gene among multiple E. coli types. We are also working on a method to detect specific antibiotic resistance genes in DNA extracted directly from feces (total community DNA). This approach will enable us to determine more precisely whether genes exist in bacteria other than those that we culture in the laboratory. This could be important if there are multiple types of bacteria that possess the genes and serve as reservoirs of these
genes. We have validated the detection limits of this approach in order to better interpret the meaning of a negative result.
Impacts
This study aims to determine the relationship between bacteria that cause disease (pathogens) and those that do not (commensals) in animals as it pertains to antibiotic resistance. Specifically, we hypothesized that this type of reservoir would explain the apparent persistence of antibiotic resistance genes, even after antibiotic use has ceased.
Publications
- No publications reported this period
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