阴沟肠杆菌纸片扩散药敏试验中抑菌环内菌落分析

Analysis of small colonies within inhibition zone in disc diffusion test of Enterobacter cloacae

目的分析阴沟肠杆菌纸片扩散药敏试验中头孢菌素抑菌环内菌落出现原因,并为纸片法药敏结果正确解释提供依据。方法从药物敏感性、β内酰胺酶等电点、诱导性和染色体DNA指纹图等方面对抑菌环内菌落和其原始株进行分析、比较。结果25/35株临床分离阴沟肠杆菌在头孢菌素抑菌环内出现小菌落。抑菌环内菌落分析显示,17株属AmpCβ内酰胺酶完全去抑制突变个体,8株属部分去抑制突变个体。结论阴沟肠杆菌纸片扩散药敏试验中头孢菌素抑菌环内菌落是其去抑制突变而高产AmpCβ内酰胺酶个体。医院感染中的阴沟肠杆菌是一个在药物敏感性上存在异源性的群体。对其抑菌环内出现耐药菌落,在排除污染后,应解释为耐药。

Objective To elucidate the reasons for presentation of small colonies in inhibitory zone in K-B diffusion test and thus to provide a basis for correct interpretation of susceptibility for Enterobacter cloacae. Methods The small colonies and their initial isolates were analyzed and compared in drug susceptibility, PI of beta-lactamase, AmpC inducibility, and PFGE fingerprints. Results 25 from 35 isolates produce zoners in the inhibitory zone of cephalosporins. The further analysis of small colonies showed that 17 strains were identified as stably depressed mutants and 8 strains were partly depressed mutants. Conclusion Zoners in the inhibitory zone of cephalosporins are AmpC beta-lactamase highproduced cells resulting from depressed mutation. Enterobacter cloacae is a highly heterogeneous population, the emergence of zoners in the inhibitory zone of cephalosporins should be considered as resistance under the circumstance of pre-excluding of contamination.