An Unusual E. coli PBP3 Insertion Sequence Identified from a Collection of Carbapenem-Resistant Enterobacteriaceae (CRE) Tested in vitro with Ceftazidime-, Ceftaroline- or Aztreonam-Avibactam Combinations [PublishAheadOfPrint]

Carbapenemase-producing Enterobacteriaceae isolates (n=110) from healthcare centers in central Indiana (2010-2013) were tested for susceptibility to combinations of avibactam (4 μg/ml) with ceftazidime, ceftaroline or aztreonam. MIC₅₀/MIC₉₀ values were 1/2 μg/ml (ceftazidime-avibactam), 0.5/2 μg/ml (ceftaroline-avibactam) and 0.25/0.5 μg/ml (aztreonam-avibactam.) A β-lactam MIC of 8 μg/ml was reported for the three combinations against one Escherichia coli isolate with an unusual TIPY insertion following Tyr344 in penicillin-binding protein 3 (PBP3) as the result of gene duplication.

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