High frequency of metronidazole resistance among strains of Campylobacter jejuni isolated from birds

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A total of 2157 strains of the enteropathogen Campylobacter jejuni were examined for resistance to metronidazole (5 mg l−1). High rates of metronidazole resistance, between 82 and 100%, were observed amongst strains of avian origin, including commercially reared broiler chickens (90.1%, n = 314) and turkeys (92%, n = 100), as well as wild birds sampled from farms and coastal environments, such as starlings (82%, n = 50), and gulls (100%, n = 20). In comparison, isolates from bovine and ovine ruminants were mostly susceptible to metronidazole, including beef cattle (17.3%, n = 653), dairy cows (19.5%, n = 251), grazing sheep (9.0%, n = 55) and lambs at slaughter (5.5%, n = 615). A moderate number of clinical isolates were resistant (62.8%, n = 99). Avian isolates had a higher average minimum inhibitory concentration (MIC) value (15 mg l−1) than cattle, lambs and clinical isolates (3 mg l−1). A June peak was observed in the percentage of metronidazole resistant strains isolated from beef cattle at slaughter. The induction of growth under aerobic and anaerobic conditions did not affect ability to grow in the presence of metronidazole among four test strains. The observations noted in this study indicate a host-phenotype relationship for which resistance to metronidazole may be a useful epidemiological marker.

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