In vitro susceptibility of characterized β-lactamase-producing Gram-negative bacteria isolated in Japan to ceftazidime-, ceftaroline-, and aztreonam-avibactam combinations

Avibactam displays potent inhibition of extended-spectrum, AmpC, KPC and some OXA β-lactamases. We examined the combinations of avibactam with ceftazidime, ceftaroline and aztreonam by the broth microdilution method against Gram-negative bacteria harboring molecularly-characterized β-lactamase genes collected in Toho University, Japan. Bacterial isolates included: Ambler class A β-lactamase-producing Enterobacteriaceae (n = 26); class C β-lactamase-producing Enterobacteriaceae (n = 9) and class D β-lactamase-producing Acinetobacter baumannii (n = 9) and Enterobacteriaceae (n = 3). Ceftazidime–avibactam, ceftaroline–avibactam ands aztreonam–avibactam were active against the strains with an extended-spectrum β-lactamase (ESBL) or AmpC enzymes, but combination with avibactam did not reduce β-lactam MICs against A. baumannii with OXA β-lactamases including carbapenemases, such as OXA-40 and -69.