Collateral Effects of Antibiotic Resistance in <i>Campylobacter jejuni</i>

Abstract Campylobacter jejuni is a leading cause of bacterial gastroenteritis worldwide, and resistance to major antibiotic classes is increasing. Exploiting collateral sensitivity (CS) may be an effective approach to optimize antibiotic use and mitigate the impact of resistance. In this study, we investigated CS and collateral resistance (CR) profiles in experimentally evolved C. jejuni mutants derived from ATCC 29428 resistant to ciprofloxacin, erythromycin, gentamicin, and tetracycline. Minimum inhibitory concentrations of thirteen antibiotics were determined in the wild-type and mutant strains to characterize collateral effects. Whole-genome sequencing was performed to identify mutations potentially underlying the observed collateral effects, and bacterial growth curves were used to evaluate the fitness of the mutants. Ciprofloxacin-resistant mutants exhibited CS most consistently to aminoglycosides, potentially explained by mutations in gyrA, parC, and parE. Gentamicin-resistant mutants showed CS to macrolides, fosfomycin, and amoxicillin. Erythromycin-resistant mutants displayed CS to aminoglycosides, albeit inconsistently across biological replicates. No CS was observed in tetracycline-resistant mutants, which showed CR to other ribosome-targeting antibiotics, potentially due to mutations in rpsJ. Consistent CR was observed among antibiotics of the same class. These findings demonstrate CS and CR patterns in C. jejuni, highlighting evolutionary trade-offs that could inform more effective treatment strategies against resistant C. jejuni infections.