Mutations in the rpsL Gene Are Involved in Streptomycin Resistance in Campylobacter coli

To characterize the mechanisms of streptomycin (STR) resistance in Campylobacter coli , we chose 17 isolates that were resistant to STR, erythromycin (ERY), or both, and the putative STR resistance target genes rpsL , rrs , and gidB were analyzed for mutations. The presence of the aadE gene encoding aminoglycoside 6-adenylyltransferase was also evaluated. To reveal putative connection between ERY and STR resistance mechanisms, 13 C. coli isolates initially susceptible to STR and ERY were exposed to STR, and resistant variants were characterized. We also assessed the development of ERY resistance with a similar method. Finally, the effect of the putative CmeABC efflux pump inhibitor phenyl-arginine-β-naphthylamine on STR resistance was tested. Our studies showed an association between mutations in the rpsL gene and STR resistance in C. coli. Further, mutations obtained in vitro were more diverse than those occurring in vivo . However, we observed no resistance associated mutations in the other genes studied, and selection with STR did not result in variants resistant to ERY and vice versa. None of the isolates harbored the aadE gene, and no differences in STR minimum inhibitory concentration levels were detected in the presence or absence of phenyl-arginine-β-naphthylamine. In conclusion, we found that STR resistance was associated with mutations in the rpsL gene, but no obvious association between STR and ERY resistance mechanisms was found in C. coli .