Antibiotic resistance in thermotolerant Campylobacter isolated in 2000/01 and 2010 from patients with diarrhoea in Dunedin, New Zealand

Objective: A pilot study to compare the antibiotic susceptibility of thermotolerant Campylobacter isolated in 2000/01 (n=60) and 2010 (n=60) from faecal samples from symptomatic patients and to subtype year-2010 isolates for epidemiological purposes. Methods: Campylobacter isolates were identified to species level by multiplex PCR. Antibiotic susceptibility testing was performed using disc diffusion and E-tests. Quinolone resistance was investigated by amplifying and sequencing the quinolone resistance determining region (QRDR) of the DNA gyrase A gene. Molecular subtyping was by restriction fragment length polymorphism of the flagellin gene, flaA. Results: Significantly more year-2000/01 isolates (15/60) were antibiotic resistant (ciprofloxacin, nalidixic acid, erythromycin and tetracycline) compared to year-2010 (P = 0.01). Resistance to ciprofloxacin, a fluoroquinolone, and nalidixic acid was detected in the year-2010 group (4/60 and 3/60 respectively); erythromycin and tetracycline resistance was not detected. Ciprofloxacin MIC were significantly lower than for year-2000/01 isolates (P = 0.02). An amino acid change in the QRDR conferring resistance was present in seven of eight isolates. Subtyping of year-2010 isolates suggested two main clusters of subtypes were present along with small groups of identical isolates. Conclusion: There was a low incidence of antibiotic resistance in thermotolerant Campylobacter isolated during a spring sampling period in Dunedin 2010. Changes in policy regarding the use of antibiotics in animals may have prevented the rapid increase in antibiotic resistant Campylobacter seen elsewhere in the world. Subtyping of year-2010 isolates indicated both diversity and commonality of sources, as previously observed for year-2000/01 isolates.