阴沟肠杆菌临床分离株对第三代头孢菌素的耐药机制研究

目的 探讨阴沟肠杆菌临床分离株对第三代头孢菌素的耐药机制。方法 运用双纸片协同试验和正交三维试验检测耐药菌株的产酶情况，通过接合传递试验和质粒谱分析等方法探讨耐药性播散的规律。结果 37株耐药菌中，产ESBLs的有2l株菌，占56．8％；产去阻遏型AmpC酶的有13株菌，占35．1％；两种酶均阳性的菌株有2株，均阴性的有l株。在同时产两种酶的2株菌中，其中l株菌CH29的两种酶均在质粒上，耐药表型可通过质粒传递到受体菌株大肠埃希氏菌ECNK5449，属于超超广谱β-内酰胺酶(SSBLs)。结论 产生ESBLs和去阻遏型AmpC酶是阴沟肠杆菌临床株对第三代头孢菌素耐药的主要机制。发现l株产SSBLs的临床分离株，可能与耐药性的水平传播有关。

Investigation on mechanism of resistance in clinical isolates of Enterobacter cloacae resistant to third- generation cephalosporins

Objective To investigate the mechanism of resistance to third-ge neration cephalosporins in clinical isolates of Enterobacter cloacae. Methods Pr oduction of beta-lactamases were identified with double-disk synergy test an d orthogonal three-dimensional extraction test.Conjugation experiments and ana lysis of plasmid profiles were performed to determine ways of transmission of re sisitance. Results Among 37 resistant strains, 21strains produced extended spect rum a-lactamases and 13 strains produced derepressed expression of AmpC a-lactamases,were 56.8% and 35.1% respectively.Two st rains,CH29 and CH11 were positive and one strain CH25 was negative in both tests .ESBLs and AmpC a-lactamases of CH29 were located on plasmids and resistanc e patterns may be transmitted to E.coli ECNK5449 as a recipent strain, so we c ould defined that CH29 produced super spectrum a-lactamase (SSBLs)]. Conclus ions Production of ESBLs and derepressed expression of AmpC a-lactamase was a predominant mechanism of resistance to third-generation cephalosporins in En terobacter cloacae clinical strains. Identification of SSBLs in clinical strain s was probably related with horizontal transfer of resistant genes.