Characterization of the ribosomal RNA methylase gene erm(A) and its promoter mutation in Campylobacter coli from chicken cecum.

Macrolide antibiotics are commonly used to treat campylobacteriosis in both clinical settings and animal husbandry. The emergence of macrolide-resistant Campylobacter poses public health risks. In this study, six Campylobacter coli strains carrying erm(A) gene were identified from chicken cecum samples, and the functionality and genetic environment of erm(A) were analyzed. Antimicrobial susceptibility testing was conducted on Campylobacter isolates. WGS was used to analyze the genetic characteristics of erm(A)-positive strains. Cloning and in vitro-induced drug resistance assay were used to investigate the function of erm(A) gene. A total of 42 (20.2 %) C. coli isolates were obtained from 208 samples collected from chicken cecum, among which 6 erm(A)-positive. Induced drug resistance assay revealed a cytosine insertion at -54 bp/-55 bp in the erm(A) promoter, leading to a 4-fold increase in erythromycin MIC. WGS analysis showed that the erm(A) gene in C. coli shared high nucleotide sequence identity with that in Enterococcus faecalis and co-located with optrA between IS1216. To the best of our knowledge, this is a report of the prevalence and characterization of erm(A)-positive C. coli from chicken cecum. A cytosine insertion at -54 bp/-55 bp in the erm(A) promoter, leading to a 4-fold increased erythromycin MIC in Campylobacter coli.