Anaerobic conditions unmask antimicrobial resistance in Vibrio cholerae

Abstract

AbstractThe antibiotic formulary is threatened by high rates of antimicrobial resistance (AMR) among enteropathogens. Enteric bacteria often undergo anaerobic respiration within the gastrointestinal tract, yet little is known about how anaerobic conditions influence AMR. The facultative enteropathogen Vibrio cholerae was chosen as a model to address this knowledge gap. V. cholerae isolates were tested for resistance under aerobic and anaerobic conditions against clinically relevant antibiotics. Using conventional breakpoints established for aerobic conditions, the odds of classifying isolates as resistant increased over 10 times for ciprofloxacin and 100 times for azithromycin under anaerobic conditions compared to aerobic conditions; for doxycycline, nearly all isolates remained sensitive. Genome-wide association studies found associations between genetic elements and AMR phenotypes that varied by oxygen exposure and antibiotic concentrations; AMR phenotypes were more heritable – and more AMR genes were discovered – under anaerobic conditions. These findings challenge the paradigm of testing facultative enteropathogens for AMR under aerobic conditions alone.