The Impact of Zinc on de novo Development of Antibiotic Resistance

Antimicrobial resistance (AMR) is a global health crisis that is predicted to worsen. While improper antibiotic usage is an established driver, less is known on the impacts of metal supplements. Here, we probe the impact of zinc (Zn) on AMR. In conflict settings where diarrhea disease cases are high, Zn, which is associated with weapons of war, is given as a supplement for diarrhea treatment prior to antibiotics such as ciprofloxacin. In this study, we find that E. coli's exposure order to zinc impacts resistance development, with increasing pre-exposure leading to accelerated ciprofloxacin resistance, while combined exposure of zinc with ciprofloxacin delays ciprofloxacin resistance. We did not find evidence that zinc pre-exposure leads to genetic changes or changes in antibiotic tolerance, though the lag phase and doubling time of E. coli was increased, suggesting gene expression may be changed. While the zinc phenotype was no longer observed if ciprofloxacin exposure did not occur right after zinc pre-exposure, the resulting elevated MIC was more stable. These results are important as they highlight the need to reexamine the clinical role of zinc in treating diarrheal diseases and assess if changes in resistance development observed in vitro are also observed in vivo. Overall design: To investigate the impact of zinc pre-exposure on resistance development, E.coli cells pre-exposed to zinc and then subinhibitory ciprofloxacin were compared against cells that were not pre-exposed to zinc prior to subinhibitory ciprofloxacin exposure. RNA-seq was then performed on 2 zinc pre-exposed samples and 1 non pre-exposed sample at the end of the pre-exposure time period. This allowed for differential gene expression to be observed between the two conditions.