Development of fluoroquinolone resistance through antibiotic tolerance in Campylobacter jejuni

Antibiotic tolerance not only enables bacteria to survive under acute antibiotic exposures but also provides bacteria with a window of time to develop antibiotic resistance. Campylobacter jejuni is increasingly resistant to clinically important antibiotics, particularly fluoroquinolones (FQs). Currently, little is known about antibiotic tolerance and its effects on resistance development in C. jejuni . Here, we show that exposure to ciprofloxacin and tetracycline at concentrations 10 and 100 times higher than the minimum inhibitory concentration (MIC) induce antibiotic tolerance in C. jejuni , whereas gentamicin and erythromycin treatment cause cell death. Interestingly, FQ resistance is rapidly developed in C. jejuni after tolerance induction by ciprofloxacin and tetracycline. Furthermore, alkyl hydroperoxide reductase plays a critical role in preventing FQ resistance development in C. jejuni during antibiotic tolerance by alleviating oxidative stress. Together, these results demonstrate that exposure of C. jejuni to antibiotics used to treat campylobacteriosis can induce antibiotic tolerance and that FQ-resistant (FQ R ) C. jejuni rapidly emerges through tolerance induction by FQs and non-FQ antibiotics. Work presented in this study shows mechanisms underlying the high prevalence of FQ R C. jejuni and provides an insight into the effects of antibiotic tolerance on resistance development. Importance Antibiotic tolerance compromises the efficacy of antibiotic treatment by extending bacterial survival and developing mutations associated with antibiotic resistance. Despite growing public health concerns about antibiotic resistance in C. jejuni , antibiotic tolerance has not yet been investigated in this important zoonotic pathogen. Here, our results show that exposure of C. jejuni to ciprofloxacin and tetracycline, a common agricultural antibiotic, develops antibiotic tolerance, which subsequently facilitates the emergence of FQ R C. jejuni . Since antibiotic-resistant C. jejuni is transmitted primarily from animals to humans, our study suggests that non-FQ drugs, such as tetracycline, used for animals can also promote FQ resistance development by inducing antibiotic tolerance in C. jejuni . Overall, the findings in this study help us understand mechanisms of resistance development through the induction of antibiotic tolerance.