4种方法检测替加环素对鲍曼不动杆菌和肠杆菌科细菌体外药敏结果分析

Evaluation of the capability of four tests for identification of the in vitro susceptibility of tigecycline against Acinetobacter and Enterobacteriaceae isolates

目的：比较四种不同药敏方法检测替加环素对鲍曼不动杆菌和肠杆菌科细菌药敏结果的不同。方法将临床分离的鲍曼不动杆菌（158株）和肠杆菌科细菌（339株）用纸片扩散法检测替加环素敏感性，对非敏感的124株细菌再分别采用微量肉汤稀释法、MTS法、琼脂稀释法检测替加环素最小抑菌浓度（ MIC），分析四种不同药敏检测方法间的差异性。结果替加环素对纸片扩散法非敏感的两种细菌均有较好的抗菌活性，MIC50大部分在敏感范围内（0．5～2 mg／L），MIC90均为4 mg／L。微量肉汤稀释法表明，替加环素对鲍曼不动杆菌和肠杆菌科细菌均有较好的抗菌活性，MIC50为1 mg／L， MIC90为4 mg／L。参照美国食品药品监督局（ FDA）和欧洲药敏试验委员会（ EUCAST）判读标准，敏感率分别为87．1％和70．2％。琼脂稀释法显示多数鲍曼不动杆菌和肠杆菌科细菌测得的替加环素MIC结果比微量肉汤稀释法高2个稀释度[基本一致性（ EA）为56．5％]，按照FDA判读标准，非常重大误差（ VME）和重大误差（ME）均为0，分类一致性（CA）为46．8％；按照EUCAST判读标准，VME为0．8％，CA为24．2％。MTS法相比于琼脂稀释法，测定替加环素对鲍曼不动杆菌和肠杆菌科细菌的药敏结果更好，MIC50为1．5 mg／L，MIC90为4 mg／L，与微量肉汤稀释法较接近，按照FDA／EUCAST判读标准，敏感率分别为83．1％／21．0％，CA分别为81．5％／29．8％，EA为71．8％，但多数细菌结果比微量肉汤稀释法高1个稀释度。FDA判读标准的相关性比EUCAST判读标准好。纸片扩散法结果表明，按照FDA判断标准， ME 为19．4％，小误差（mE）为71．8％。本研究未出现VME菌株，但CA仅为8．9％。结论纸片法、MTS法、琼脂稀释法与微量肉汤稀释法均存在差异，其中以MTS法与微量肉汤稀释法相关性最好，且FDA判读标准相比于EUCAST判读标准相关性更好。建议临床检测替加环素体外药敏试验，可参照美国FDA判读标准，通过纸片法常规检查，对于纸片法中介或耐药的菌株再进行MTS法进行确认，必要时可进行微量肉汤稀释法做进一步确证试验。

Objective To evaluate the capability of four tests for identification of the in vitro suscepti-bility of tigecycline against Acinetobacter and Enterobacteriaceae isolates.Methods Disk diffusion test was per-formed to detect the sensitivity of 158 Acinetobacter and 339 Enterobacteriaceae isolates to tigecycline.The mini-mum inhibitory concentrations （ MICs） of tigecycline for non-sensitive isolates were detected by using broth dilu-tion method （ BDM） , MIC Test Strip （ MTS） and agar dilution method.The differences with antimicrobial sus-ceptibility among the four different methods were evaluated.Results Tigecycline showed good antibacterial ac-tivity against both non-sensitive Acinetobacter and Enterobacteriaceae isolates with most of the MIC50 values in the sensitivity range of （0.5-2） mg/L and all of the MIC90 values of 4 mg/L.The MIC50 and MIC90 values measured by BDM were respectively 1 mg/L and 4 mg/L.The sensitivity rates presented by the results of BDM were re-spectively 87.1%and 70.2%based on the standards made by Food and Drug Administration （FDA） and Euro-pean Committee on Antimicrobial Susceptibility Testing （ EUCAST） .Agar dilution method indicated that most of the MICs of tigecycline to Acinetobacter and Enterobacteriaceae isolates were two dilutions higher than those de-tected by BDM with essential agreement （EA） rate of 56.5%.Both the very major error （VME） and the major error （ME） values were 0 and the categorical agreement （CA） rate was 46.8%according to the FDA standard.The VME and CA values were 0.8% and 24.2% based on EUCAST standard.Compared with agar dilution method, MTS showed better results in determining the susceptibility of Acinetobacter and Enterobacteriaceae iso-lates to tigecycline with MIC50 and MIC90 values of 1.5 mg/L and 4 mg/L, which was similar to the capability of BDM.Referring to the FDA and EUCAST standards, the sensitivity rates were 83.1% and 21.0%, the CA rates was 81.5%and 29.8%, and the EA rate was 71.8%.Most of the results tested by MTS were one dilution higher than those by BDM.FDA standard showed better correlation than EUCAST standard.Disk diffusion method showed the ME, mE, VME and CA values were respectively 19.4%, 71.8%, 0 and 8.9%according to FDA standard.Conclusion Disk diffusion method, MTS and agar dilution method all showed differences with BDM in susceptibility testing.The capability of MTS was similar to that of BDM.The results evaluated by FDA standard were better than those by EUCAST standard.The in vitro susceptibility of bacteria to tigecycline could be tested by disk diffusion method using FDA standard for evaluation, and confirmed with MTS if isolates were resistance or intermediate strains.The BDM could be performed for further confirmation if necessary.