Molecular Typing and Antimicrobial Resistance of Campylobacter Isolated During Commercial Broiler Production
Hernandez, Charles Andrew
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Campylobacter jejuni is a commensal microorganism of the poultry gastrointestinal tract. Broilers, layers, ducks, turkeys, and quails can be colonized by Campylobacter without illness occurring. The vast majority of human Campylobacter infections are recognized as being foodborne. For 2008, preliminary FoodNet data showed that the Campylobacter incidence of infection, 12.68 per 100,000 of the U.S. population, is the second highest, only behind Salmonella at 16.20 per 100,000. To further understand Campylobacter?s role as a foodborne pathogen, analysis at the molecular level is needed. Microbial molecular typing allows for identification and differentiation of bacterial strains beneath the species level. In this study, the ?gold standard? method for molecular subtyping, Pulsed Field Gel Electrophoresis (PFGE), along with Diversilab? repetitive element Polymerase Chain Reaction (rep-PCR) and 16S-23S Internal Spacer Region Denaturing Gradient Gel Electrophoresis (ISR DGGE) were used for the molecular typing of Campylobacter jejuni isolates obtained during different stages of commercial broiler production and processing. In addition, the C. jejuni isolates were tested for resistance to antimicrobials commonly used in both veterinary and human medicine. Antimicrobial resistance testing was carried out using a broth dilution system. The majority of recovered isolates came from post-harvest carcass rinsates. Carcass rinses were obtained at post-evisceration, post-chill stages. All isolates (n = 46) were identified by the Polymerase Chain Reaction as Campylobacter jejuni. Three genotypes (n = 44, n = 1, n = 1) were identified by PFGE. The 46 rep-PCR products grouped into seven clusters and two outliers. Clustering of rep-PCR products by sample source was not observed. No relatedness trends were observed for isolates recovered from the same source. The combination of PFGE and Diversilab rep-PCR methods provides highly discriminatory molecular typing results. These results provide practical epidemiological information that shows postevisceration and post-chill stages are still important targets for intervention studies. The very high occurrence of C. jejuni isolates exhibiting genotype A suggests it may differentially express certain gene(s) that enable this strain to more favorably survive under the different harsh environmental conditions encountered during production and processing. In addition, phenotypic testing revealed all of the isolates were not resistant to the antimicrobials azithromycin, ciprofloxacin, erythromycin, gentamycin, tetracycline, florfenicol, nalidixic acid, telithromycin, and clindamycin at any of the concentrations tested. All the C. jejuni isolates exhibited an indistinguishable two-band 16S-23S ISR DGGE profile. Overall, these C. jejuni commercial broiler pre- and post-harvest isolates exhibited an extremely low degree of molecular and phenotypic variability.