Results from the China Antimicrobial Surveillance Network (CHINET) in 2017 of the <i>In Vitro</i> Activities of Ceftazidime-Avibactam and Ceftolozane-Tazobactam against Clinical Isolates of <i>Enterobacteriaceae</i> and <i>Pseudomonas aeruginosa</i>

Abstract

The <i>in vitro</i> activities of ceftazidime-avibactam (CZA), ceftolozane-tazobactam (C-T), and comparators were determined for 1,774 isolates of <i>Enterobacteriaceae</i> and 524 isolates of <i>Pseudomonas aeruginosa</i> collected by 30 medical centers from the China Antimicrobial Surveillance Network (CHINET) in 2017. Antimicrobial susceptibility testing was performed by the CLSI broth microdilution method, and <i>bla</i>_KPC and <i>bla</i>_NDM were detected by PCR for all carbapenem-resistant <i>Enterobacteriaceae</i> (CRE). Ceftazidime-avibactam demonstrated potent activity against almost all <i>Enterobacteriaceae</i> (94.6% susceptibility; MIC₅₀, ≤0.25 mg/liter; MIC₉₀, ≤0.25 to >32 mg/liter) and good activity against <i>P. aeruginosa</i> (86.5% susceptibility; MIC_50/90, 2/16 mg/liter). Among the CRE, 50.8% (189/372 isolates) were positive for <i>bla</i>_KPC-2, which mainly existed in ceftazidime-avibactam-susceptible <i>Klebsiella pneumoniae</i> isolates (92.1%, 174/189). Among the CRE, 17.7% (66/372 isolates) were positive for <i>bla</i>_NDM, which mainly existed in strains resistant to ceftazidime-avibactam (71.7%, 66/92). Ceftolozane-tazobactam showed good <i>in vitro</i> activity against <i>Escherichia coli</i> and <i>Proteus mirabilis</i> (MIC_50/90, ≤0.5/2 mg/liter; 90.5 and 93.8% susceptibility, respectively), and the rates of susceptibility of <i>K. pneumoniae</i> (MIC_50/90, 2/>64 mg/liter) and <i>P. aeruginosa</i> (MIC_50/90, 1/8 mg/liter) were 52.7% and 88.5%, respectively. Among the CRE strains, 28.6% of <i>E. coli</i> isolates and 85% of <i>K. pneumoniae</i> isolates were still susceptible to ceftazidime-avibactam, but only 7.1% and 1.9% of them, respectively, were susceptible to ceftolozane-tazobactam. The rates of susceptibility of the carbapenem-resistant <i>P. aeruginosa</i> isolates to ceftazidime-avibactam (65.7%) and ceftolozane-tazobactam (68%) were similar. Overall, both ceftazidime-avibactam and ceftolozane-tazobactam were highly active against clinical isolates of <i>Enterobacteriaceae</i> and <i>P. aeruginosa</i> recently collected across China, and ceftazidime-avibactam showed activity superior to that of ceftolozane-tazobactam against <i>Enterobacteriaceae</i>, whereas ceftolozane-tazobactam showed a better effect against <i>P. aeruginosa</i>.