RESUMO
BACKGROUND: Acquired antimicrobial resistance among Achromobacter isolates from cystic fibrosis (CF) patients is frequent. Data concerning the mechanisms involved are scarce. The role of the AxyXY-OprZ and AxyEF-OprN Resistance Nodulation Division (RND) efflux systems has been demonstrated, but not that of AxyABM. OBJECTIVES: To explore the role of efflux systems in the acquired multiresistance observed in a one-step mutant selected after ofloxacin exposure. METHODS: The in vitro resistant mutant NCF-39-Bo2 and its parental strain NCF-39 (MICs of meropenem of 8 and 0.19 mg/L, of ceftazidime of 12 and 3 mg/L, of cefiderocol of 0.094 and 0.032 mg/L and of ciprofloxacin of 8 and 1.5 mg/L, respectively) were investigated by RNA-seq and WGS. Gene inactivation and reverse transcription quantitative PCR (RT-qPCR) were used to explore the role of the efflux systems of interest. RESULTS: RNA-seq showed that the AxyABM efflux system was overproduced (about 40-fold) in the in vitro mutant NCF-39-Bo2 versus its parental strain NCF-39. A substitution in AxyR, the putative regulator of AxyABM, was detected in NCF-39-Bo2. Gene inactivation of axyB (encoding the transporter component) in NCF-39-Bo2 led to a decrease in MICs of ciprofloxacin (5-fold), meropenem (64-fold), ceftazidime (12-fold) and cefiderocol (24-fold). Inactivation of axyB in the clinical isolate AXX-H2 harbouring a phenotype of resistance close to that of NCF-39-Bo2 enhanced the activity of the same molecules, especially meropenem. CONCLUSIONS: AxyABM overproduction is involved in acquired resistance of Achromobacter to ciprofloxacin, meropenem and ceftazidime, antibiotics widely used in CF patients, and increases the MIC of the new promising antibiotic cefiderocol.