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Title: The multiple antibiotic resistance locus in salmonella from animals.
Author: Randall, Luke Patrick.
ISNI:       0000 0001 3507 4665
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2000
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In order to understand the role of the Multiple Antibiotic Resistance (mar) locus in the Biology of Salmonella, a Typhimurium DT104 marA:: g fp:: cam reporter mutant was constructed. Expression of mar in Salmonella, as observed for E. coli, did induce low level multiple antibiotic resistance and cyclohexane resistance. However, mar expression in Salmonella did not appear to down regulate OmpF as has been observed for E. coli. Both in-vitro and in-vivo tests suggested that mar contributed to the virulence of Salmonella. The exact mechanism whereby mar contributes to virulence is uncertain. It could be that insertional inactivation of mar limits the ability of Salmonella to up regulate a ToIC type porin, which in Enteritidis has been linked to virulence. Wild type Salmonella were screened for cyclohexane resistance as a possible way of detecting naturally occurring mar mutants. Cyclohexane resistance occurred in about one to five percent of wild type Salmonella tested. These strains had a typical mar phenotype as regards low level multiple antibiotic resistance, cyclohexane resistance and down regulated OmpF, but none of the strains tested had mutations in marOR. Passage of wild type Salmonella strains on media with tetracycline and chloramphenicol gave rise to multiple antibiotic resistant and cyclohexane resistant mutants. The mutants with higher level antibiotic resistance generally lacked OmpF although these mutants lacked mutations in marOR in general. The high degree of specificity required to induce mar and the low level of antibiotic resistance conferred by its induction suggest that mar in itself is unlikely to confer clinical antibiotic resistance in Salmonella. However, higher levels of resistance were seen in the mar like mutants generated and for strains grown with salicylate. Coupled with the involvement of mar in virulence, it is possible that mar and related regulatory systems such as acrAB, rob and sox could have important roles in antibiotic resistance and virulence of Salmonella. 2
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available