Thesis
Evidence for dissemination of clonally related Escherichia coli strains carrying extended-spectrum B-lactamase CTX-M in Washington State dairy farms
Washington State University
Master of Science (MS), Washington State University
2014
Handle:
https://hdl.handle.net/2376/100952
Abstract
The rapid dissemination of CTX-M worldwide is a matter of concern. To assess the clonal dissemination of blaCTX-M-positive E. coli, we compared blaCTX-M-positive E. coli strains and blaCTX-M-negative E. coli strains using several different typing methods. A total of 126 blaCTX-M-positive E. coli strains and 126 blaCTX-M-negative E. coli strains were obtained from fecal samples from cattle in 18 dairy farms in three different regions of Washington State during summer-fall 2012. Multi-locus sequence typing (MLST) and Pulsed-field gel electrophoresis (PFGE) were performed for all the isolates. In addition, we compared 75 blaCTX-M-positive E. coli strains, 75 blaCTX-M-negative E. coli strains and 50 uropathogenic E. coli strains using MLST and a newly proposed two-locus (fumC/fimH) CH typing method to examine the suitability of the CH typing method as a molecular typing method for commensal E. coli. The 126 blaCTX-M-positive E. coli isolates were more clonally related, as assessed by multi-locus sequence typing and pulsed-field gel electrophoresis in comparison to 126 blaCTX-M-positive E. coli that were highly diverse. Thirty-two and 76 STs were identified among blaCTX-M-positive and blaCTX-M-negative E. coli isolates that clustered into three and ten clonal complexes (CC), respectively. CC10 (n= 63, 50%) was the dominant clone in blaCTX-M- positive E. coli isolates. Sixty-seven and 113 distinct PFGE types were identified among blaCTX-M-positive and blaCTX-M-negative E. coli isolates which clustered into 24 and 32 clusters, respectively. Within farms and between farms, common clones and PFGE clusters were observed. The results suggested that CH typing is a less suitable typing method for commensal E. coli than MLST because the latter had equal or greater discriminatory power than CH typing when used for blaCTX-Mnegative and blaCTX-M-positive E. coli isolates, while CH typing was more discriminatory than MLST when used on UPEC. This study revealed that blaCTX-M-positive E. coli isolates are clonally disseminated among healthy cattle within the same dairy farms and between different farms in different regions in Washington State. Tracking and monitoring of blaCTX-M genes in food animals will provide information that is critical for preventing dissemination of antibiotic resistance elements to humans via the food chain.
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Details
- Title
- Evidence for dissemination of clonally related Escherichia coli strains carrying extended-spectrum B-lactamase CTX-M in Washington State dairy farms
- Creators
- Sara Ahmed Labib Ahmed
- Contributors
- Margaret A. Davis (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, Washington] :
- Identifiers
- 99900525170601842
- Language
- English
- Resource Type
- Thesis