Impaired Fitness and Transmission of Macrolide-Resistant Campylobacter jejuni in Its Natural Host

Abstract

ABSTRACTCampylobacter jejuniis a major zoonotic pathogen transmitted to humans via the food chain and is prevalent in chickens, a natural reservoir for this pathogenic organism. Due to the importance of macrolide antibiotics in clinical therapy of human campylobacteriosis, development of macrolide resistance inCampylobacterhas become a concern for public health. To facilitate the control of macrolide-resistantCampylobacter, it is necessary to understand if macrolide resistance affects the fitness and transmission ofCampylobacterin its natural host. In this study we conducted pairwise competitions and comingling experiments in chickens using clonally related and isogenicC. jejunistrains, which are either susceptible or resistant to erythromycin (Ery). In every competition pair, Ery-resistant (Eryr)Campylobacterwas consistently outcompeted by the Ery-susceptible (Erys) strain. In the comingling experiments, EryrCampylobacterfailed to transmit to chickens precolonized by ErysCampylobacter, while isogenic ErysCampylobacterwas able to transmit to and establish dominance in chickens precolonized by EryrCampylobacter. The fitness disadvantage was linked to the resistance-conferring mutations in the 23S rRNA. These findings clearly indicate that acquisition of macrolide resistance impairs the fitness and transmission ofCampylobacterin chickens, suggesting that the prevalence of macrolide-resistantC. jejuniwill likely decrease in the absence of antibiotic selection pressure.