The in vitro activities of ceftazidime-avibactam, ceftolozane-tazobactam and comparators were determined for 1,774 isolates of Enterobacteriaceae and 524 isolates of Pseudomonas aeruginosa collected by 30 medical centers across China in 2017. Antimicrobial susceptibility testing was performed by CLSI broth microdilution. And blaKPC and blaNDM were detected by PCR for all carbapenem-resistant Enterobacteriaceae (CRE). Ceftazidime-avibactam demonstrated potent activity against almost all Enterobacteriaceae (94.6% susceptibility; MIC50≤0.25 mg/L; MIC90, ≤0.25- >32 mg/L) and good against P. aeruginosa (86.5% susceptibility; MIC50/90, 2/16 mg/L). blaKPC-2 was positive among 50.8% (189/372) of the CRE, mainly existed in ceftazidime-avibactam susceptible K. pneumoniae (92.1%, 174/189). blaNDM were positive among 17.7% (66/372) of the CRE and mainly existed in strains resistant to ceftazidime-avibactam (71.7%, 66/92). Ceftolozane-tazobactam showed good in vitro activity against E. coli and P. mirabilis (MIC50/90, ≤0.5/2; 90.5 and 93.8% susceptibility), and susceptibility of K. pneumoniae (MIC50/90, 2/>64 mg/L) and P. aeruginosa (MIC50/90, 1/8 mg/L) were 52.7% and 88.5%. Among the CRE strains, 28.6% of E. coli and 85% of K. pneumoniae were still susceptible to ceftazidime-avibactam, but only 7.1% and 1.9% of them were susceptible to ceftolozane-tazobactam. Susceptibility rates of the carbapenem-resistant P. aeruginosa 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 Enterobacteriaceae and P. aeruginosa collected recently across China. And ceftazidime-avibactam was superior against Enterobacteriaceae than ceftolozane-tazobactam, whereas the latter showed better effect against P. aeruginosa.
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