Master's Theses



Degree Name

Master of Science (MS)


Multi-drug-resistant bacteria are a major cause of hospital-acquired infections and antibiotic resistance in these organisms is often plasmid mediated, which has become a growing concern. Plasmids conferring resistance to multiple antibiotics are increasingly becoming a common source of antibiotic resistance. The behavior of these plasmids under and in the absence of selective pressure is not yet fully understood. Therefore, to determine the behavior of a multiple-resistance plasmid under selective pressure pCR 2.1-TOPO, a commercial plasmid, was inserted into an Escherichia coli host and grown in a continuous culture under four conditions: broth with 1) kanamycin alone, 2) ampicillin alone, 3) with both kanamycin and ampicillin, and 4) without antibiotics. Samples were taken every two weeks, frozen, and later cultured on a replica plate series to identify mutants whose plasmids no longer conferred resistance to one or both antibiotics. The plasmids of these mutants were isolated, sequenced, and compared. The sequence data were analyzed to determine how the plasmid-mediated resistance genes changed over time. These results show the effects of selection pressure on the plasmid itself rather than on the organism by antibiotics and relates to the overall problem of antibiotic resistance in medicine and animal science by contributing to the understanding of the persistence of resistance markers in pathogen populations.


Dr. Eric Gillock

Date of Award

Spring 2013

Document Type



© 2013 Justin W.R. Kerby II


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