Antimicrobial activity of ceftazidime–avibactam and comparator agents when tested against bacterial isolates causing infection in cancer patients (2013–2014)

Abstract

We evaluated the antimicrobial susceptibility of 623 Gram-negative organisms causing infection in patients with cancer in 52 United States hospitals (2013–2014) as part of the International Network for Optimal Resistance Monitoring (INFORM) program. Isolates were tested for susceptibility by broth microdilution method. β-lactamase encoding genes were evaluated for all Escherichia coli and Klebsiella spp. with an extended-spectrum β-lactamase (ESBL) phenotype by microarray-based assay. ESBL-phenotype was observed among 17.3 and 9.9% of E. coli and Klebsiella pneumoniae, respectively; and 25.0% of Enterobacter cloacae were ceftazidime-non-susceptible. All Enterobacteriaceae (n=486) were susceptible to ceftazidime-avibactam (MIC50/90, 0.12/0.25μg/mL) with the highest MIC value at 1μg/mL. Meropenem was active against Enterobacteriaceae overall (MIC50/90, ≤0.06/≤0.06μg/mL; 99.6% susceptible); but showed more limited activity against Klebsiella spp. with an ESBL-phenotype (84.6% susceptible) and multidrug-resistant Enterobacteriaceae (93.3% susceptible). The most active agents tested against Pseudomonas aeruginosa were colistin (100.0% susceptible), amikacin (97.7% susceptible) and ceftazidime-avibactam (96.6% susceptible).