Objective To investigate the reasons of less susceptibility mechanism to cefepime (FEP)than to ceftazidime (CAZ)in clinical isolates of Pseudomonas aeruginosa.Methods A total of 60 isolates of Pseudomonas aeruginosa which had been tested being less susceptible to FEP than to CAZ for minimal inhibitory concentration (MIC) by Vitek 2 Compact automatic microorganism analyzer system were collected.Agar dilution method was used to reexamine the MIC of FEP and CAZ.The resistance genes were amplified by polymerase chain reaction (PCR).The expressions of efflux system were analyzed by real-time fluorescence quantitation PCR.Results The 5% of error rate was showed between agar dilution method and Vitek 2 Compact system.There were isolates with KPC and PSE-1 resistance genes by PCR amplification.There were mainly the expressions of mexB and mexD in efflux system.The sequencing of regulatory genes showed that there were 3 isolates for mexB which the Gly70(GGG)of nalC was substitute for Glu(GAG)(GGG→GAG)and 2 isolates for mexD which the Gly1 09(GGC)of nfxB was substitute for Val (GTC) (GGC→GTC).Conclusions Less susceptibility to FEP than to CAZ in clinical isolates of Pseudomonas aeruginosa is due to the production of KPC and PSE-1 resistance genes and the increasing expression levels of mexAB-OprM and mexCD-OprJ.%目的：探讨临床分离的铜绿假单胞菌对头孢吡肟（FEP）敏感性低于头孢他啶（CAZ）的原因。方法收集临床分离的经 Vitek 2 Compact 全自动微生物分析系统检测 PEF 最小抑菌浓度（MIC）高于 CAZ MIC 的铜绿假单胞菌60株，琼脂稀释法复查 FEP 和 CAZ 的 MIC 值，聚合酶链反应（PCR）扩增耐药基因，实时荧光定量 PCR分析细菌外排系统表达情况。结果手工琼脂稀释法检测与 Vitek 2 Compact 全自动微生物分析系统检测存在5％的差别，PCR 扩增发现部分菌株存在编码 KPC 和 PSE-1的耐药基因，外排系统表达显示以 mexB 和 mexD 为主。测序结果发现 mexB 的3个调控基因只有 nalC Gly70→Glu（GGG→GAG）改变，其他2组调控基因未发现有意义的突变，mexD 外排系统过度表达的调控基因出现 nfxB Gly109→Val（GGC→GTC）。结论FEP 敏感性低于CAZ 的主要原因可能是编码 KPC 与 PSE-1的耐药基因的存在和外排系统 mexAB-OprM、mexCD-OprJ 表达增加共同作用的结果。
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