MOLECULAR EPIDEMIOLOGY OF CAMPYLOBACTER AND YERSINIA
ENTEROCOLITICA ISOLATES FROM PIGS REARED IN CONVENTIONAL AND
ANTIBIOTIC FREE FARMS FROM DIFFERENT GEOGRAPHIC REGIONS
DISSERTATION
Presented in Partial Fulfillment of the Requirements for
the Degree Doctor of Philosophy in the Graduate School
of The Ohio State University
By
Daniel Alemayehu Tadesse, D.V.M
* * * * *
The Ohio State University
2009
Dissertation Committee: Approved by
Professor Wondwossen A. Gebreyes, Advisor
Professor Fred DeGraves Advisor
Professor Paivi Rajala-Schultz Graduate Program in
Professor Thomas E. Wittum Veterinary Preventive Medicine
Copyright by
Daniel Alemayehu Tadesse
2009
ABSTRACT
This dissertation is composed of four studies conducted in two predominant
bacterial pathogens; Campylobacter spp. and Yersinia enterocolitica in swine production
systems. While the main scope was focused on molecular epidemiology, antimicrobial
resistance has also been a key component of the studies. Campylobacter are one of the
leading causes of foodborne bacterial infections. The first study was conducted to
determine the prevalence and antimicrobial resistance profile of Campylobacter in 34
farm-slaughter pairs from conventional and antimicrobial free (ABF) pig farms representing four different states classified into two regions (region 1 – Ohio and
Michigan; region 2 – Wisconsin and Iowa) . A total of 838 fecal and 1173 carcass samples were examined. Campylobacter isolation was done following recommended protocol and speciated using multiplex PCR targeting ceuE and hipO genes. The minimum inhibitory concentration was determined using agar dilution to a panel of six antimicrobials (chloramphenicol, erythromycin, gentamicin, ciprofloxacin, nalidixic acid and tetracycline). The overall Campylobacter prevalence was 56.3%. We found
Campylobacter prevalence of 58.9% and 53.7% among conventional and antimicrobial
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free farms, respectively (p=0.24). There was no significant difference between region 1
(54.1%) and region 2 (58.2%) (p=0.92). Carcass Campylobacter contamination was
found at slaughter followed by a significant reduction at post chill. Antimicrobial
resistance was found to all tested antimicrobials with different frequency. Higher proportions of Campylobacter were resistant to tetracycline (64.5%) and erythromycin
(47.9%). Resistance to chloramphenicol (4.4%), gentamicin (3.2%), nalidixic acid
(23.5%) and ciprofloxacin (4.9%) were also detected. Forty-six of 61 ciprofloxacin resistant (75.4%) Campylobacter coli were recovered from ABF and the remaining 15
(24.6%) from conventional production systems. Thirty-seven out of 1257 Campylobacter coli (2.9%) were resistant to both erythromycin and ciprofloxacin, drugs of choice for human campylobacteriosis. High prevalence of Campylobacter coli and high proportion
of resistance in both conventional and ABF systems, regardless of antimicrobial use status, was found.
The emergence and spread of fluoroquinolone resistant Campylobacter poses a
great challenge to public health. In the second study, we evaluated the contribution of point mutations in the quinolone resistance determining region (QRDR) of the gyrA gene to quinolone resistance. A total of eighty Campylobacter isolates were selected based on minimum inhibitory concentration (MIC) of ciprofloxacin and nalidixic acid. Of these, 21 were resistant to both ciprofloxacin (MIC ≥ 4 μg/ml) and nalidixic acid (MIC ≥ 32
μg/ml), 19 were resistant to nalidixic acid only and the remaining forty were susceptible
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to both ciprofloxacin and nalidixic acid. Of the 21