Colistin does not potentiate ceftazidime-avibactam killing of carbapenem-resistant Enterobacteriaceae in vitro or suppress emergence of ceftazidime-avibactam resistance [PublishAheadOfPrint]

We tested ceftazidime-avibactam and colistin against 24 carbapenem-resistant Enterobacteriaceae (CRE) by time-kills. Ceftazidime-avibactam (0.25x, 1x, 4x MIC) was bactericidal against 8%, 21%, and 88% of isolates, respectively. Colistin (2μg/mL) was bactericidal against 83% (12 hours) and 42% (24 hours) of isolates. In combination, synergy and antagonism was identified against 13% and 46% of isolates, respectively. The combination did not suppress ceftazidime-avibactam resistance. Colistin plus ceftazidime-avibactam did not provide benefit over ceftazidime-avibactam against most CRE isolates.

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