| dc.description.abstract | Campylobacter is an internationally recognized food-borne pathogen of public health
importance. Food animals are important reservoirs of Campylobacter species, of which swine
are known to be a main reservoir of Campylobacter coli. Conventionally reared swine
receive antimicrobials in their feed at sub-therapeutic concentrations to enhance their growth;
this use has been under debate due to associations with the development of antimicrobial
resistant (AR) bacterial strains. However, AR bacteria are also shed by swine reared under no
antimicrobial selection pressure, highlighting the potential role played by other factors
including environmental reservoirs in the transmission of AR strains to pigs which needs to
be identified.
The objectives of this study were to 1) determine the Campylobacter prevalence and
antimicrobial resistance profile in the ABF and conventional swine production systems at
farm, slaughter, and the environment, 2) determine associations between potential risk factors
and the prevalence of AR C. coli at the pre-harvest level, and 3) compare the population
biology of antimicrobial resistant C. coli in the two systems. C. coli was the predominant
species isolated at farm, slaughter, and environment in both production systems. The
persistence of multidrug-resistant (MDR) C. coli in all the farm and slaughter stages in our
study clearly indicates the ability of C. coli strains to disseminate across the production chain
and persist in the farm and slaughter environment. Associations were determined between exposure to enrofloxacin, tetracycline, tiamulin, and resistance to ciprofloxacin and nalidixic
acid, tetracycline, and macrolides, respectively in C. coli isolated from conventional pigs.
The high frequency of MDR C. coli isolated from pigs reared in the ABF system, which did
not receive antimicrobials for treatment or growth promotion, clearly indicate the lack of
antimicrobial use does not necessarily result in absence of AR bacterial populations. Multiple
MDR patterns were observed in the ABF pigs, including resistance to seven antimicrobials.
Associations between swine management practices and the prevalence of AR C. coli
in the ABF and conventional productions systems revealed the presence of cattle, and the
presence of pigs with diarrhea to be potential risk factors for the C. coli prevalence and AR in
swine farms. Data analysis identified plastic farrowing floors, the use of antiparasitics,
cleaning ≤ 1week prior to the pigs entry to the barns, and the use of a glutaraldehide and
ammonium chloride solution in addition to chlorhexidine, to be significantly associated with
a lower prevalence of AR Campylobacter.
Multilocus sequence typing (MLST) of the C. coli populations from ABF and
conventional swine production systems revealed freely recombining populations close to
linkage equilibrium. Identical sequence types (STs) between the pigs and their environment,
both at farm and slaughter, were detected. The close clustering of C. coli STs from swine and
carcasses with those from the environment revealed a C. coli population that shares a
common ancestry in the conventional and ABF swine production systems. This could
potentially explain the high prevalence of AR C. coli in ABF production systems.
Overall, our results highlight the definitive role of the environment in the persistence
and dissemination of AR Campylobacter, particularly in alternative swine production systems that do not use antimicrobials. The phenotypic and genotypic similarity of C. coli
isolates from the two production systems, and the environmental reservoirs present in ABF
and conventional farms could potentially explain antimicrobial resistance in pigs that were
not exposed to antimicrobials. | |
