During the past decade there has been a considerable increase in the number of antibiotics to which bacteria have become resistant. Dissemination of antibiotic resistance is attributed to horizontal gene transfer, principally by the process of conjugation. This investigation sought to assess the potential for dissemination by measuring the frequencies of conjugation of antibiotic resistance markers amongst micro-organisms of the gastrointestinal tract particularly gene transfer between Gram-positive and Gram-negative bacteria. Conjugation experiments utilising filter matings showed the ability. of Gram-positive plasmids pIP50 I and pRE39 to conjugally transfer and disseminate antibiotic resistance between a wider range of Gram-positive food-borne pathogens and food processing bacteria than had been reported previously. By contrast the previously reported conjugal transfer of pIP501 from Gram-positive Enterococcus faecalis to Gram-negative Escherichia coli (Kurenbach et af. 2003) could not be confirmed. However, chloramphenicol resistant colonies of E.coli were produced following attempted filter matings using Gram-positive Efaecalis as donor. Stringent analyses of these E.coli strains produced both in this study and by Kurenbach et af (2003) found no evidence for the presence of pIP50 I-derived sequences or the chloramphenicol acetyl transferase (CAT) antibiotic resistance gene product. Further investigations determined that the presence of certain chloramphenicol resistance plasmids was required in Gram-positive Efaecalis to facilitate the isolation of chloramphenicol resistant E.coli colonies. Subsequent proteomic analyses of these chloramphenicol resistant E.coli mutants revealed a change in level of expression ofTolC and Sip consistent with constitutive expression of the marRAB operon responsible for multiple antibiotic resistance due to efflux. Therefore it appears that Gram-positive bacteria may contribute to the dissemination of antibiotic resistance without the requirement for horizontal gene transfer by facilitating the induction of an intrinsic antibiotic resistance phenotype in Gram-negative bacteria.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:491940 |
| Date | January 2008 |
| Creators | Forgrave, Richard William John |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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