Concentrations of ciprofloxacin in food defined as safe alter the gut microbiome and ciprofloxacin susceptibility in humans: an interventional clinical study

It is unknown if the low residual concentrations of ciprofloxacin/enrofloxacin allowed in food could influence the human microbiome. The European Medicines Agency reports that it is safe for an average human to ingest 372 µg of enrofloxacin/ciprofloxacin daily. We randomized 30 individuals to either 372 µg of ciprofloxacin or placebo daily for 27 days in a 2:1 fashion and measured the effect on the gut microbiome and the susceptibility of Escherichia coli to ciprofloxacin. After 27 days the E. coli of the individuals in the ciprofloxacin, but not the placebo arm, had reduced ciprofloxacin susceptibility. The receipt of ciprofloxacin was also associated with a reduction in the number of E. coli colony forming units in the gut. The low concentration of antimicrobials allowed in food may have an impact on the composition of the gut microbiome and antimicrobial susceptibility.