Unusual Escherichia coli PBP 3 Insertion Sequence Identified from a Collection of Carbapenem-Resistant Enterobacteriaceae Tested In Vitro with a Combination of Ceftazidime-, Ceftaroline-, or Aztreonam-Avibactam

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