Phenotypic and Genotypic characterization of Campylobacter isolated in swine from Conventional and Antimicrobial free farms

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Title: Phenotypic and Genotypic characterization of Campylobacter isolated in swine from Conventional and Antimicrobial free farms
Author: Thakur, Siddhartha
Advisors: Glen Almond, Committee Member
Craig Altier, Committee Member
Wondwossen Gebreyes, Committee Chair
Maria Correa, Committee Member
Abstract: Campylobacter is the leading cause of bacterial foodborne infections in the world. Campylobacter coli is an important species and ranks second to Campylobacter jejuni in causing clinical infection in humans in the United States. Pigs have been shown to be the major reservoir of this pathogen at the pre-harvest level in conventional swine farms where antimicrobials are used for therapeutic and growth promotion purposes. Another important facet of the swine industry is the interest in the antimicrobial free (ABF) production systems. The projected increase of 20-30% in the consumption of food products reared under antimicrobial free conditions in the United States necessitates the need to determine the status of major foodborne pathogens such as Campylobacter in swine reared under the ABF system. The purpose of this study was to determine the prevalence, antimicrobial resistance and the genetic diversity of Campylobacter isolated from swine reared in the two production systems at preharvest and during slaughter process. To better understand the epidemiology of this pathogen in the ABF system, similar comparisons were made between ABF herds reared in intensive units barns to those reared in the extensive environment. C. coli was the predominant species (99%) isolated from both the systems. High prevalence observed at the nursery level indicates that sows could act as an important source of transmission. The role played by environmental factors in transmission was highlighted by higher prevalence observed in ABF pigs reared outside with free access to soil and water. Significant reduction in prevalence was seen at the slaughter level though C. coli were isolated from post-chill samples. We recommend adding an intervention step after chilling and before packaging of the pork product. Highest frequency of resistance was seen against tetracycline and erythromycin in both the systems. We found significant association between antimicrobial resistance and the conventional production system. High frequency of pansusceptible isolates from the ABF system could be due to the absence of selective pressure of antimicrobials. Resistance against the fluoroquinolone ciprofloxacin and multidrug resistant C. coli in both systems points to the role of other unknown selective pressures and /or risk factors besides antimicrobial use. This is the first study in the US reporting ciprofloxacin resistant C. coli from swine. Ciprofloxacin resistance in C. coli is concerning as this antimicrobial is used for treating severe cases of campylobacteriosis in humans. Multilocus sequence typing was found to be a better method compared to pulsed field gel electrophoresis for genotyping C. coli based on its discriminatory power and throughput. High genetic diversity of C. coli was observed in the swine production systems as indicated by the weak clonal structure of the isolates tested. Evidence of a lineage in the ABF system will help in comparing C. coli isolates from different parts of the world. Linkage equilibrium between the housekeeping genes in isolates from the two systems could explain the high antimicrobial resistance exhibited by ABF pigs irrespective of use of antimicrobials at the farm. Overall, this study highlights the dissemination of antimicrobial resistant C. coli in swine irrespective of the production system. Resistance detected in the absence of antimicrobial selective pressure highlights the role played by unknown factors that need to be determined. We recommend studies that should be focussed on finding these sources so that effective preharvest control measures could be implemented. Finally, we recommend genotyping more isolates to better understand the epidemiology of C. coli in the swine environment.
Date: 2005-11-02
Degree: PhD
Discipline: Comparative Biomedical Sciences
URI: http://www.lib.ncsu.edu/resolver/1840.16/4440


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