圆环估计试验检测诱导型AmpC-β-内酰胺酶

Detection of inducible AmpC-β-lactamases in gram-negetive bacilli by Kirby-Bauer disc approximation test

目的了解肠杆菌科细菌中产诱导型AmpC-β-内酰胺酶的情况。方法 建立一种圆环估计试验(KBDA)的检测方法,以头孢西丁作为诱导剂,第三代头孢菌素(头孢他啶和头孢噻肟)作为指示剂,观察抑菌圈的大小和在诱导剂一边抑菌圈形状的改变。结果 诱导剂引起抑菌圈形状的改变被分为S、B、C、D、R型,其中诱导型产AmpC酶耐药细菌(C型和D型)占67.5％,这些细菌对庆大霉素和环丙沙星的敏感率分别为85％和93％。结论 KBDA试验能检测出传统的K-B或MIC药敏试验所不能发现的诱导型产AmpC酶对第三代头孢菌素的耐药,可加用庆大霉素或环丙沙星来提高疗效。

Objective To investigate the occurrence of inducible AmpC-β-lactamases in enterobacteriaceae. Methods Kirby-Bauer disc approximation test ( KBDA ) was developed in this study. Cefoxitin was used as an indu-cer agent for the induction of AmpC-β-lactamases. Ceftazidime and cefotaxime were used for the third generation cephalosporin susceptibility reporter agent. The interpretation of such drug susceptibility was based on the combination of the size of the antibiotic zone-of-inhibition and the growth patterns of a zone near a potent inducer agent. Results Based on the types of zone distortion around eeftazidime or cefotaxime, a gradient of five types of susceptibi-lity( S ,B ,C ,D,R) was readily discernable to reflect continous levels of resistance to eeftazidime and cefotaxime,as a result of various degrees of AmpC induction. Among 40 clinical isolates of gram-negative bacilli tested, 67.5% isolates (C and D type) exhibited identifiable phenotypes of inducible resistance to the third generation cephalosporins. Percentages of inducible resistance isolates susceptible to gentamicin and ciprofloxacin were 85% and 93% , respectively. Conclusion The KBDA test can be applied as a phenotype screening method for detection of inducible AmpC-β-lactamases in gram-negative bacilli, while this standard KB disc diffusion or MIC is unable to measure. Treatment of infections caused by inducible resistance isolates may be benefited from the combination of β-lactams with gentamicin or ciprofloxacin.