Genetic basis and clonal population structure of antibiotic resistance in Campylobacter jejuni isolated from broiler carcasses in Belgium

Authors: ELHADIDY, MOHAMED - Mansoura University; Miller, William - Bill; ARGUELLO, HECTOR - Universidad De Cordoba; ÁLVAREZ-ORDÓÑEZ, AVELINO - University Of Leon; DUARTE, ALEXANDRA - Ghent University; DIERICK, KATELIJNE - Scientific Institute Of Public Health; BOTTELDOORN, NADINE - Scientific Institute Of Public Health

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2018
Publication Date: 5/17/2018
Citation: Elhadidy, M., Miller, W.G., Arguello, H., Álvarez-Ordóñez, A., Duarte, A., Dierick, K., Botteldoorn, N. 2018. Genetic basis and clonal population structure of antibiotic resistance in Campylobacter jejuni isolated from broiler carcasses in Belgium. Frontiers in Microbiology. 9:1014. https://doi.org/10.3389/fmicb.2018.01014.
DOI: https://doi.org/10.3389/fmicb.2018.01014

Interpretive Summary: The food-borne pathogen Campylobacter is a natural contaminant of most birds and livestock, with poultry meat the major vehicle for Campylobacter-associated illness in humans. This study analyzed the antibiotic resistance of Campylobacter jejuni strains from chicken broilers. Resistance was tested against five antibiotics: ciprofloxacin, nalidixic acid, tetracycline, gentamicin, and erythromycin. Roughly half of the strains were resistant to ciprofloxacin, nalidixic acid and tetracycline, while a lower proportion were resistant to gentamicin or erythromycin. 11% of the strains were multidrug resistant (resistant to three or more classes of antibiotics). The genetic basis of resistance was characterized. Many of the resistant strains contained genes or mutations previously associated with antimicrobial resistance. However, in some resistant strains, the genetic basis of resistance could not be determined, indicating that additional uncharacterized genes or chromosomal mutations can confer drug resistance in Campylobacter. The data generated from this study will help to address food security and public health challenges resulting from C. jejuni infection.

Technical Abstract: The aim of this study was to investigate the population structure and antimicrobial resistance profiles of a set of Campylobacter jejuni strains isolated from broiler carcasses in Belgium, and to further analyze the molecular mechanisms responsible for the resistance phenotypes. Minimum inhibitory concentrations against five commonly-used antibiotics (ciprofloxacin, nalidixic acid, tetracycline, gentamicin, and erythromycin) were determined for 204 non-duplicate C. jejuni strains using the standard broth dilution method. More than half of the C. jejuni isolates were resistant to ciprofloxacin or nalidixic acid (53.9% and 53.4%, respectively). A total of 96 strains (47%) were resistant to tetracycline. In contrast, a lower percentage of screened isolates were resistant to gentamicin or erythromycin (6.9% and 4.9%, respectively). Moreover, 11 out of the 204 resistant C. jejuni isolates (5.4%) were found to be multiply drug resistant (i.e., resistant to three or more antibiotic classes). The molecular determinants of resistance were further studied in isolates resistant to quinolones (ciprofloxacin and nalidixic acid), the macrolide erythromycin, and tetracycline. C. jejuni isolates resistant to ciprofloxacin and/or nalidixic acid were screened for the substitution Thr-86-Ile in the quinolone resistance determining region (QRDR) of the gyrA gene, while C. jejuni isolates resistant to tetracycline were screened for the presence of the tet(O) gene. These resistance determinants were observed in most but not all resistant isolates. Regarding resistance to erythromycin, different mutations occurred in diverse genetic loci, including mutations in the 23S rRNA gene, the rplD and rplV ribosomal genes, and the intergenic region between cmeR and cmeABC. Other erythromycin-resistant isolates harboured the ermB gene. Interestingly, and contrary to previous reports, the A2075G transition mutation in the 23S rRNA gene was only found in one strain displaying a high level of resistance to erythromycin. This study suggests that other mechanisms of resistance, that remain to be elucidated, may also contribute to the resistant phenotypes observed. Ultimately, this study provides better understanding of the epidemiology and the molecular basis of antibiotic resistance in C. jejuni, which will prove useful for the development of more effective C. jejuni control strategies.