In vitro and in vivo reduced fitness and virulence in ciprofloxacin-resistant Acinetobacter baumannii.

Limited data on relative fitness and virulence of antimicrobial-resistant Acinetobacter baumannii are known. We aimed to study the virulence and fitness cost of ciprofloxacin-resistance in A. baumannii (CipR) compared with the susceptible parental wild-type strain (CipS). Human lung epithelial cells were infected with CipS and CipR for 24 h. Competition fitness was monitored in vitro and in vivo in a murine peritoneal sepsis model. We showed that CipR induced less cell death than CipS and CipR growth was slow when in competition with CipS. Altogether, acquisition of ciprofloxacin resistance confers a biological fitness cost and reduces virulence in A. baumannii.