Genetic characterization of Multidrug resistant strains of Campylobacter coli from turkeys in North Carolina

Abstract

Commercial turkey flocks in North Carolina are frequently colonized with Campylobacter coli strains that are resistant to several antimicrobials and have been designated multidrug resistant (MDR). Multiple locus sequence typing (MLST) showed that the major sequence types (STs) were turkey-specific. Further subtyping using fla typing, pulsed field gel electrophoresis (PFGE) with SmaI and KpnI as well as plasmid profiles revealed that each of the major MDR STs contained strains of related, but distinct subtypes, providing evidence for genomic diversification within these STs. Numerous strains, with indistinguishable PFGE profiles, but different fla types suggested selection for specific flagellin sequences. The observed correlation between STs and the MDR profiles of the microbes indicates that MLST-based typing holds potential for source-tracking applications specific to the animal source (turkeys) and the antimicrobial resistance profile (MDR) of C. coli. The molecular basis for resistance of MDR strains to selected antimicrobials was investigated, and tetracycline resistant isolates were shown to harbor tet(O). Natural transformation studies were used to study the mechanism of transfer of antibiotic resistance genes in C. coli. Resistance to erythromycin and nalidixic acid/ciprofloxacin mediated by chromosomal sequences, were easily transferred from MDR strains to other C. coli, whereas resistance to tetracycline and kanamycin was not possible by transformation, suggesting that genes mediating these resistance attributes were plasmid-borne in MDR strains. Interestingly, tetracycline resistance could be readily transferred by transformation using DNA from another clonal group of C. coli strains prevalent in turkeys, suggesting chromosomal presence of the tetracycline resistance gene. MDR strains were found to be stable and maintained their MDR phenotype over 60 serial passages in vitro. The strains maintained their PFGE and plasmid profiles; and only minor differences in MICs before and after the 60 passages were observed. The findings from this study suggest that the certain strain types and clonal groups are prevalent among MDR C. coli from turkeys, and that resistance determinants to certain antibiotics can be transferred from these MDR strains to other C. coli strains.