双纸片氯唑西林增效试验检测高产AmpC酶的阴沟肠杆菌

Detecting high level AmpC β-lactamase among clinical isolates of Enterobacter cloacae by means of cloxacillin-potentiated disc diffusion test

目的 尝试建立易于操作、适合临床应用的检测高产 Amp C酶阴沟肠杆菌的方法。方法 在标准头孢他啶、头孢噻肟、头孢曲松、氨曲南纸片上分别附加 0、10、2 0、30、4 0、5 0 μg氯唑西林 ,按标准纸片扩散试验程序分别测定未附加氯唑西林时和附加氯唑西林后上述纸片对 10 8株受试菌的抑菌环直径 ,根据氯唑西林对 4种抗生素的增效作用判断受试菌是否高产 Amp C酶 ,检测结果与头孢西丁三维试验的结果进行对比。结果 三维试验证实 ,在 10 8株阴沟肠杆菌中 ,高产 Amp C酶菌株 32株 ,非高产 Amp C酶菌株 76株。以 5 0 μg氯唑西林为酶抑制剂时 ,如果分别考虑头孢他啶、头孢噻肟、头孢曲松、氨曲南作为药敏指示剂时的检测结果 ,双纸片氯唑西林增效试验的阳性率分别为 90 .6 % (2 9/ 32 )、6 8.8% (2 2 / 32 )、6 5 .6 % (2 1/ 32 )、5 9.4 % (19/ 32 ) ;如果同时考虑头孢他啶和头孢噻肟 (或头孢曲松 )作为药敏指示剂时的检测结果 ,双纸片氯唑西林增效试验的阳性率达到了 10 0 % (32 / 32 )。同样条件下 ,用双纸片氯唑西林增效试验检测 76株非高产 Amp C酶的阴沟肠杆菌 ,未发现假阳性菌株。结论 以 5 0 μg氯唑西林为酶抑制剂、联合使用头孢他啶和头孢噻肟 (或头孢曲松 )作为药敏指示剂 。

Objective To establish a convenient method for detecting high-level AmpC β-lactamase producers in Enterobacter cloacae . Methods One hundred and eight nonduplicate isolates of Enterobacter cloacae were collected and inhibitory zone diameters of ceftazidime, cefotaxime, ceftriaxon and aztreonam were measured alone or in combination with cloxacillin by standard disc diffusion test. Three-dimensional extract test was simultaneously performed on all isolates. Results Among 108 isolates, 32 were confirmed by positve three- dimensional tests to produce high level AmpC β-lactamase. When 50μg of cloxacillin was used as inhibitor and only one of ceftazidime, cefotaxime, ceftriaxone and aztreonam was used as indicator, the sensitivity of the cloxacillin- potentiated disc diffusion test was 90.6%(29/32), 68.8%(22/32), 65.6%(21/32) and 59.4% (19/32) , respectively. When 50μg of cloxacillin was used as inhibitor and both ceftazidime and cefotaxime (or both ceftazidime and cefotriaxone) were used as indicators, the sensitivity of the test increased to 100% (32/32) . No false positive strain was found when 76 strains with negative three -dimensional tests were assayed by the new method. Conclusion The new cloxacillin-potentiated disc diffusion test was a reliable method for detecting high-level AmpC producing Enterobacter cloacae when both ceftazidime and cefotaxime (or both ceftazidime and cefotriaxone) were used as indicators and 50μg of cloxacillin was used as inhibitor.