"Acceptable" concentrations of enrofloxacin in food lead to reduced enrofloxacin susceptibility in a mouse model of gastrointestinal Klebsiella pneumoniae

Concentrations of antimicrobials up to 1,000-fold lower than the minimum inhibitory concentration can select for antimicrobial resistance. This generates the hypothesis that the low concentrations of antimicrobials allowed in our food could select for resistance. We assessed if the dose of enrofloxacin allowed in food by the European Medicines Agency (6.2 µg/kg) could decrease susceptibility to enrofloxacin in a strain of Klebsiella pneumoniae colonizing the gastrointestinal tracts of Specific Opportunistic Pathogen-Free Naval Medical Research Institute (NMRI) mice. We found that one-tenth of this dose given daily was able to increase the K. pneumoniae enrofloxacin MIC 8-fold (from 0.047 µg/mL to 0.38 µg/mL). Our findings suggest the need for studies to assess if the same could occur in humans.