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Transfer Frequency of CMY-2-Encoding Plasmids Among Fecal Flora of Pigs

Dodson, Kathryn Kristine
http://rave.ohiolink.edu/etdc/view?acc_num=osu1395851225

Abstract Details

2005, Master of Science, Ohio State University, Veterinary Preventive Medicine.
Plasmid-encoded CMY-2, an AmpC-like ß-lactamase, has disseminated rapidly worldwide and conveys resistance to a wide variety of antibiotics. CMY-2 was used as a model system to study the in vitro fitness and the in vivo persistence and conjugal transfer rates of antibiotic resistance genes. In vitro: CMY-2-encoding plasmid DNA was electroporated into E. coli DH10B. Two large plasmids (>194 kb) transferred resistance to cefoxitin, cephalothin, tetracycline, and ampicillin and intermediate resistance to ceftriaxone and ceftiofur to E. coli DH10B. The growth curves of the transformed and non-transformed E. coli DH10B were very similar. Filter mating of the transformed E. coli DH10B with three unique Salmonella strains did not result in transconjugants, regardless of variation in donor: recipient ratios, incubation temperature, and enrichment. The CMY-2-encoding plasmid does not convey a significant metabolic burden to the host bacteria and is not readily transferred between bacteria in vitro. Challenge 1: Ten weaned, three-week-old pigs were randomly assigned to two groups. The first group of five pigs was orally inoculated with CMY-2-containing Salmonella, while the other five served as a control. No antibiotics were administered throughout the challenge period. Fecal samples were obtained and ceftiofur-resistant Salmonella and commensal E. coli were isolated. Recovered ceftiofur-resistant isolates had two distinct plasmid profiles, corresponding to non-lactose-fermenting flora (including Salmonella) and E. coli. The E. coli plasmid profile did not share plasmids of the same size with the Salmonella inoculum and all ceftiofur-resistant E. coli isolates were blaCMY-2 negative. The frequency of conjugative transfer of blaCMY-2 from the Salmonella donor to commensal E. coli recipient was <3.0x10-8. A non-CMY-2 mechanism of ceftiofur resistance disseminated throughout the commensal E. coli population, despite the absence of ceftioufur resistant flora in pre-challenge screening. In the absence of antibiotic selective pressure, the in vivo conjugal transfer rate of CMY-2 from Salmonella to E. coli is very low in the pig gastrointestinal tract. Challenge 2: Sixteen three-week-old, weaned pigs were randomly divided into four treatment groups (TG). TGI received an oral inoculation of CMY-2-containing E. coli DH10B and were fed medicated feed. TG2 also received an oral inoculation of CMY-2- containing E. coli DH10B, but were fed non-medicated feed. TG3 were not challenged with CMY-2-containing E. coli DH10B and were fed medicated feed, while TG4 served as a control and did not receive oral inoculation or medicated feed. Each pig was orally inoculated with naladixic-acid resistant Salmonella. Fecal samples were obtained and ceftiofur-resistant E. coli and Salmonella were isolated. Ceftiofur-resistant E. coli shedding was not significantly affected by treatment with medicated feed (Repeated measures ANOVA, p=0.08). The frequency of conjugative transfer of blaCMY-2 from the E. coli DH10B to naladixic-acid resistant Salmonella was <3.4x10-8. These results provide further evidence that antibiotic selective pressure is not solely responsible for the dissemination of antibiotic resistance genes. In the presence and absence of antibiotic selective pressure, the in vivo conjugal transfer rate of CMY-2 from E. coli DH10B to naladixic-acid Salmonella is very low in the pig gastrointestinal tract. To determine if differences in the magnitude of ceftiofur-resistant E. coli shedding across treatment groups were repeatable, another challenge was performed. Fecal isolates were obtained from pigs orally inoculated with CMY-2-containing E. coli DH10B, and four control pigs. Both groups were given medicated feed. The prevalence of ceftiofur- resistant E. coli shedding was consistently similar among co-housed pigs and did not depend upon treatment. Persistence of antibiotic resistance genes in the environment may play a role in the dissemination of antibiotic resistance genes.
Jeffrey LeJeune (Advisor)
Julie Funk (Committee Member)
Daral Jackwood (Committee Member)
74 p.
Animal Diseases

Recommended Citations

Citations

  • Dodson, K. K. (2005). Transfer Frequency of CMY-2-Encoding Plasmids Among Fecal Flora of Pigs [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1395851225

    APA Style (7th edition)

  • Dodson, Kathryn. Transfer Frequency of CMY-2-Encoding Plasmids Among Fecal Flora of Pigs. 2005. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1395851225.

    MLA Style (8th edition)

  • Dodson, Kathryn. "Transfer Frequency of CMY-2-Encoding Plasmids Among Fecal Flora of Pigs." Master's thesis, Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1395851225

    Chicago Manual of Style (17th edition)

osu1395851225
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© 2005, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.