Objectives: Campylobacter is a major foodborne enteric pathogen and macrolides are the drug of choice for the clinical therapy of campylobacteriosis. Macrolide resistance among Campylobacter compromises clinical treatment, is associated with adverse health events and is a significant public health concern. Here, we report the first identification of a horizontally transferrable macrolide resistance mechanism in porcine Campylobacter coli ZC113 that is mediated by a ribosomal RNA methylase, Erm(B).
Methods: Horizontal transfer of a macrolide resistance determinant between C. coli and Campylobacter jejuni was performed by natural transformation. Whole-genome sequencing was initially used to identify the ribosomal methylase-encoding gene erm(B) in Campylobacter. Cloning of erm(B) into C. jejuni NCTC 11168 was performed to evaluate whether the erm(B) gene is responsible for high-level macrolide resistance in Campylobacter.
Results: The erm(B) gene was identified in ZC113, conferred high-level resistance to macrolides and was associated with a chromosomal multidrug-resistant genomic island (MDRGI). The MDRGI probably originated from Gram-positive bacteria and was horizontally transferred between C. coli and C. jejuni via natural transformation. Furthermore, the erm(B)-positive isolate ZC113 was resistant to all clinically important antibiotics used for treating campylobacteriosis and is essentially multidrug-resistant Campylobacter.
Conclusions: To the best of our knowledge, this is the first report of a horizontally transferable macrolide resistance mechanism in thermophilic Campylobacter. Surveillance of erm(B) and its associated MDRGI in both C. coli and C. jejuni is urgently warranted.
Keywords: campylobacteriosis; food safety; foodborne enteric pathogens; macrolide treatment.