Status of antimicrobial resistance in clinical isolates of Campylobacter jejuni and Campylobacter coli in Australia

The aim of this study was to investigate the prevalence of resistance to six antimicrobials in Campylobacter jejuni and Campylobacter coli isolates from gastroenteritis cases using phenotypic antimicrobial susceptibility testing (AST) and whole genome sequencing (WGS). Resistance rates in Australia were compared to European Food Safety Authority data (EFSA) and the United States Centers for Disease Control and Prevention’s (CDC) National Antimicrobial Resistance Monitoring System. A total of 164 Campylobacter isolates (137 C. jejuni and 27 C. coli) were collected from patients with campylobacteriosis from eight Australian states and territories from October 2018 to February 2019 and tested for susceptibility to six antimicrobials using ETEST® strips. Genomic DNA was sequenced using the Illumina NextSeq platform and resistance genes identified from assembled WGS sequences using the Nullarbor pipeline and ResFinder. Phenotypically, 14.0%, 20.1%, 1.8% and 14.6% of isolates were resistant to ampicillin, ciprofloxacin, erythromycin and tetracycline, respectively. All isolates tested were susceptible to amoxicillin-clavulanic acid and gentamicin with no resistance detected. We identified twelve resistance genes, namely aad9, aadE, aph(3’)Illa, blaOXA-61, blaOXA-184, blaOXA-185, blaOXA-449, blaOXA-625, catA, erm(B), sat4, tet(O), and mutations in the gyrA and 23S rRNA genes. For each antimicrobial tested, concordance between resistance phenotype and genotype ranged from 33.3 to 100.0%. Compared to the United States and countries in Europe, Australia has low rates of ciprofloxacin and tetracycline resistance. Although one in five isolates were resistant to ciprofloxacin, most (98.2%) were susceptible to erythromycin, the drug of choice for treating Campylobacter infection.