LONGITUDINAL SURVEILLANCE AND COMBINATION ANTIMICROBIAL SUSCEPTIBILITY TESTING OF MULTIDRUG-RESISTANT ACHROMOBACTER SPP. FROM CYSTIC FIBROSIS PATIENTS

Background:Achromobacter spp. are recognized as an emerging pathogen in patients with Cystic Fibrosis (CF). Though recent works have established species-level identification using nrdA sequencing, there is a dearth in knowledge relating to species-level antimicrobial susceptibility patterns and antimicrobial combinations which hampers the use of optimal antimicrobial combinations for the treatment of chronic infections. The aims of this study were i) to identify at species-level referred Achromobacter isolates ii) to describe species-level antimicrobial susceptibility profiles iii) to determine the most promising antimicrobial combination for chronic Achromobacter infections.Methods: A total of 112 multidrug-resistant (MDR) Achromobacter spp. isolates from 39 patients were identified using nrdA sequencing. Antimicrobial susceptibility and combination testing were carried out using the Etest method.Results: We detected six species of Achromobacter and found that A. xylosoxidans was the most prevalent species. Interestingly, sequence analysis showed it was responsible for persistent infection (18/28 patients) followed by A. ruhlandii (2/3 patients). Piperacillin-tazobactam (70.27%) and cotrimoxazole (69.72%) were the most active antimicrobials. Differences were observed in species-level susceptibility to ceftazidime, carbapenems, ticarcillin-clavulanate, and tetracycline. Antimicrobial combinations with cotrimoxazole or tobramycin demonstrate the best synergy while cotrimoxazole gave the best susceptibility breakpoint Index values.Conclusions: This study enriches the understanding of MDR Achromobacter spp. epidemiology, confirms prevalence and chronic colonization of A. xylosoxidans in CF lungs. It presents in vitro data to support the efficacy of new combinations for use in the treatment of chronic Achromobacter infections.