Longitudinal Surveillance and Combination Antimicrobial Susceptibility Testing of Multidrug-Resistant Species from Cystic Fibrosis Patients.

spp. are recognized as emerging pathogens in patients with cystic fibrosis (CF). Though recent works have established species-level identification using 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 to (i) identify at species-level referred isolates, (ii) describe species-level antimicrobial susceptibility profiles, and (iii) determine the most promising antimicrobial combination for chronic infections. A total of 112 multidrug-resistant (MDR) species isolates from 39 patients were identified using sequencing. Antimicrobial susceptibility and combination testing were carried out using the Etest method. We detected six species of and found that was the most prevalent species. Interestingly, sequence analysis showed it was responsible for persistent infection (18/28 patients), followed by (2/3 patients). Piperacillin-tazobactam (70.27%) and co-trimoxazole (69.72%) were the most active antimicrobials. Differences were observed in species-level susceptibility to ceftazidime, carbapenems, ticarcillin-clavulanate, and tetracycline. Antimicrobial combinations with co-trimoxazole or tobramycin demonstrate the best synergy, while co-trimoxazole gave the best susceptibility breakpoint index values. This study enriches the understanding of MDR spp. epidemiology and confirms prevalence and chronic colonization of in CF lungs. It presents data to support the efficacy of new combinations for use in the treatment of chronic infections.