Risk factors for antibiotic resistance in Campylobacter spp. isolated from raw poultry meat in Switzerland

Abstract

Background: The world-wide increase of foodborne infections with antibiotic resistant pathogens is of growing concern and is designated by the World Health Organization as an emerging public health problem. Thermophilic Campylobacter have been recognised as a major cause of foodborne bacterial gastrointestinal human infections in Switzerland and in many other countries throughout the world. Poultry meat is the most common source for foodborne cases caused by Campylobacter. Because all classes of antibiotics recommended for treatment of human campylobacteriosis are also used in veterinary medicine, in view of food safety, the resistance status of Campylobacter isolated from poultry meat is of special interest.

Methods: Raw poultry meat samples were collected throughout Switzerland and Liechtenstein at retail level and examined for Campylobacter spp. One strain from each Campylobacter-positive sample was selected for susceptibility testing with the disc diffusion and the E-test method. Risk factors associated with resistance to the tested antibiotics were analysed by multiple logistic regression.

Results: In total, 91 Campylobacter spp. strains were isolated from 415 raw poultry meat samples. Fifty-one strains (59%) were sensitive to all tested antibiotics. Nineteen strains (22%) were resistant to a single, nine strains to two antibiotics, and eight strains showed at least three antibiotic resistances. Resistance was observed most frequently to ciprofloxacin (28.7%), tetracycline (12.6%), sulphonamide (11.8%), and ampicillin (10.3%). One multiple resistant strain exhibited resistance to five antibiotics including ciprofloxacin, tetracycline, and erythromycin. These are the most important antibiotics for treatment of human campylobacteriosis. A significant risk factor associated with multiple resistance in Campylobacter was foreign meat production compared to Swiss meat production (odds ratio = 5.7).

Conclusion: Compared to the situation in other countries, the data of this study show a favourable resistance situation for Campylobacter strains isolated from raw poultry meat produced in Switzerland. Nevertheless, the prevalence of 19% ciprofloxacin resistant strains is of concern and has to be monitored. "Foreign production vs. Swiss production" was a significant risk factor for multiple resistance in the logistic regression model. Therefore, an adequate resistance-monitoring programme should include meat produced in Switzerland as well as imported meat samples.

Figure 1

Distribution and classification of retail shops. Distribution and classification of the 122 retail shops included in this study. Green dots: shops without Campylobacter-positive samples. Yellow dots: shops with at least one Campylobacter-positive sample; no antibiotic resistance. Orange dots: shops with at least one sample with Campylobacter resistant to one of the tested antibiotics. Red dots: shops with at least one sample with Campylobacter resistant to more than one antibiotic.

Figure 2

Results of E-test method. Results of susceptibility testing to ciprofloxacin, erythromycin and tetracycline using the E-test method. Susceptible strains are marked in blue. Strains with a minimal inhibition concentration (MIC) higher than the breakpoint value for resistance are marked in red.

Figure 3

Resistance according to production system and to origin. Comparison of antibiotic resistance in Campylobacter spp. isolated from conventional (n = 50) and, animal-friendly' (n = 37) products and from foreign (n = 24) and Swiss (n = 63) products, respectively.