Thesis
Evolution of multiple antimicrobial drug resistance: conservation of genes encoding streptomycin, sulfonamide and tetracycline resistance among Escherichia coli with increasing multi-drug resistance
Washington State University
Master of Science (MS), Washington State University
2007
Handle:
https://hdl.handle.net/2376/102275
Abstract
Commensal E. coli may serve as a reservoir of resistance genes transferable to pathogens and may also at as foci for "assembly" of multi-drug resistance (MDR). MDR to streptomycin, sulfonamide and tetracycline (R-type SSuT) is particularly frequent among E. coli isolated from cattle, either alone (3-drug resistance) or in combination with additional resistance phenotypes (SSuT+). We hypothesized that SSuT+ strains are assembled from a backbone of conserved SSuT resistance determinants and therefore compared the locations (chromosomal vs. plasmid) of different resistance genes in E. coli isolated from clinically normal cattle. Streptomycin resistance conferring genes (strA, strB) and a sulfonamide conferring gene (sul2) were largely conserved across the range of MDR commensal E. coli. Consistent with the hypothesis, an additional sulfonamide resistance gene, sul1, was detected more frequently in isolates with higher level MDR but the distribution of tetracycline resistance genes was inconsistent with the hypothesis as the frequency of tet(B) decreased and the frequency of tet(A) increased in R-type SSuT8+ isolates; relatively few high-level MDR isolates retained tet(B). The locations of the resistance genes were also unconserved, being universally non-plasmid encoded in the R-type SSuT but increasingly plasmid-encoded in isolates with increasing MDR. Together, these observations suggest that R-type SSuT+ isolates do not evolve directly from R-type SSuT isolates and that some other process must account for the conservation of the SSuT phenotype in SSuT+ isolates.
Metrics
11 Record Views
Details
- Title
- Evolution of multiple antimicrobial drug resistance
- Creators
- Renu Joseph
- Contributors
- Thomas E. Besser (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Veterinary Medicine, College of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525061301842
- Language
- English
- Resource Type
- Thesis