基于K-B法筛选异质性耐药菌株及其对抗菌药物敏感试验结果的影响

Screening of heterogeneous strains and its effect on antimicrobial susceptibility tests based on K-B method

目的探讨K-B法抑菌圈内出现细菌单菌落的可能原因及其对药敏结果的影响。方法采用头孢他啶和美罗培南药敏纸片对革兰阴性菌株进行筛选,对抑菌圈内出现的细菌单菌落进行鉴定及药敏试验,并与原鉴定结果和药敏结果进行比较。结果从痰液,尿液,血液等临床标本分离的2 500株革兰阴性杆菌。55株在头孢他啶或美罗培南纸片抑菌圈内会出现肉眼可见的细菌单菌落,其中26株经过了菌落纯培养,出现异质性耐药23株,污染3株,29株未经过菌落纯培养,出现异质性耐药14株,污染15株。头孢他啶纸片筛选试验中,共有28株抑菌圈中菌株与原鉴定结果一致,但耐药表型及具体药敏结果均发生改变,其中7株阴沟肠杆菌氨曲南和头孢曲松药敏结果均从敏感变成耐药。美罗培南纸片筛选试验中,共有9株抑菌圈中菌株与与原鉴定结果一致,其中7株铜绿假单胞菌氨曲南从敏感变为中介,亚胺培南从中介变为耐药。结论本研究中,1.48%革兰阴性杆菌分离菌株会出现异质性耐药,菌落传代纯培养可以有效降低药敏操作过程中的污染。异质性耐药菌株的存在以及实验操作过程中的可能污染对病原菌体外药敏结果的影响,需要引起临床,特别是临床微生物工作者的关注和重视。

Objective To investigate the reasons for the emergence of bacteria in inhibition zone by K-B disc diffusion method and its influence on the result of antimicrobial susceptibility test.Methods Ceftazidime(CAZ)and Meropenem(MEM)were used to screen Gram-negative bacteria.The strains in the inhibition zones of CAZ or MEM were selected and compared with the original bacteria after identification and antimicrobial susceptibility test.Results 55 of the 2,500 strains collected from sputum,urine,blood and other specimens were found to have visible strains in the inhibition zones of CAZ or MEM.Among the 26 strains of pure-cultured bacteria,23 strains showed heteroresistance while 3 strains were contaminated.Among the 29 strains of non-pure-culured bacteria,14 strains had heteroresistance while 15 strains were contaminated.The 28 strains of bacteria in the inhibition zones of CAZ showed the same identification results but different resistant phenotypes and antimicrobial susceptibility profiles compared to parental strains,in which 7 Enterobacter cloacae strains changed from sensitive to resistant against Aztreonam(ATM)and Ceftriaxone(CRO).The 9 strains of bacteria in the inhibition zones of MEM exhibited the same identification results,in which 7 Pseudomonas aeruginosa strains changed from sensitive to intermediate against ATM and from intermediate to resistant against CRO.Conclusion 1.48%of Gram-negative bacteria showed heteroresistance to CAZ and MEM.Bacterial subculture can reduce the contamination effectively in the course of antimicrobial susceptibility test.The results of antimicrobial susceptibility test were affected by the heteroresistant strains and the contaminated strains.