Antibiotic resistance in the food chain : a case study of Campylobacter spp. in poultry.
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Date
2013
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Abstract
The sub-therapeutic use of antibiotics for growth promotion in food animal production,
has engendered substantial debate on the dissemination of antibiotic resistance via the
food chain, specifically, the probability of antibiotic use in food production creating a
reservoir of resistant bacteria and/or resistance genes that may spread to humans
thereby limiting the therapeutic value of antimicrobial drugs. In the absence of any
surveillance programme on food-borne bacteria in South Africa, this study focussed on
Campylobacter spp. in poultry and encompassed a literature review on the prevailing
debate on the dissemination of antibiotic resistance via the food chain, a phenotypic
observational study on the prevalence and antibiotic resistance profiles of
Campylobacter spp. isolated within and across different poultry farming systems and a
genotypic component that covered identification methods, plasmid profile
determination and strain typing. Identification methods for Campylobacter spp., viz, biochemical tests and matrix
assisted laser desorption ionization- time of flight (MALDI-TOF) mass spectrometry
was compared to the PCR which is considered the gold standard as a molecular method
of identification. The MALDI-TOF was shown to be superior to the biochemical tests
for the identification of C. coli but equivalent to the biochemical tests for C. jejuni. Of
the 363 samples collected in total, the frequency of thermophilic Campylobacter was 68
% in rural farms (or informally reared poultry), 47 % in both commercial free-range
and industrial broilers and the highest in industrial layers at 94 %. Antibiotic resistance
analysis showed that isolates from the rural farming systems were significantly (P < 0.01) more susceptible to ciprofloxacin, tetracycline and erythromycin when compared
to the other farming systems. Significant (P < 0.001) antibiotic resistance differences
were detected between broilers (5 - 8 week lifespan), and layers (36 - 52 week lifespan)
for gentamicin, ciprofioxacin and tetracycline.
Plasmids were fonnd be harboured by isolates in all the farming systems; in 84 % of
isolates from free-range broilers, 77 % of isolates from industrial broilers, 83 % of
isolates from industrial layer hens and 75 % of isolates from the rural farming system.
The PFGE genotyping of 42 Campylobacter isolates generated 39 SmaI types.
Substantial and substantive genetic diversity was observed between and within farming
systems. The lack of correlations amongst the parameters within and between farming
systems attested to the diversity and complexity of phenotypes and genotypes and
indicated de novo evolution in response to antibiotic selection pressure and animal
husbandry practices.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2013.
Keywords
Campylobacter infections in poultry., Theses--Medical biochemistry.