| Objective:To analyze the effects of culture time and medium for Carba NP test(CNP).The rapid Carba NP test(RCNP)was developed to evaluate the effect of detection of carbapenemase,and compared with the modified Hodge test(MHT),Carba NP test,modified carbapenem inactivation method(mCIM).The "0.5 + 9h incubation mode" of mCIM was developed to evaluate the clinical application of its value.The inhibitor enhanced modified carbapenem inactivation method(imCIM)was developed to explore the value of detection of class B carbapenemase,and compared with EDTA disc potentiation test(EDPT).To provide multi-index analysis research for clinical laboratory in epidemiological investigation,nosocomial infection control and resistant genotyping.Methods:1 264 strains from clinical separation were served as object,this collection of strains included 69 Klebsiella Pneumoniae,60 Escherichia coli,68 Acinetobacter baumanii,67 Pseudomonas aeruginosa,all strains were grown for 6h,12 h,24h and stored for 7 days with blood agar for Carba NP test,respectively.2 Carba NP test was conduct to be detect carbapenemase production,all strains were grown on China Blue agar,MacConkey agar,MH agar,Nutrient agar,Nutrient agar supplemented with Zn SO4.3 The rapid Carba NP test was established by homemade carbapenemase assay and used rub instead of incubation.Used PCR results as a gold standard.And compared with modified Hodge test,Carba NP test and modified carbapenem inactivation method.4 Detect carbapenemase production underwent mCIM for “0.5+9h incubation mode”.Screened class B carbapenemase underwent imCIM andEDPT,the date was analyzed by consistency check,McNemar χ2 test,related-sample Wilcoxon signedrank sum test and ROC curve.Results:1 The sensitivity and specificity of the Carba NP test was 95.1%(121/144)and 96.7%(116/120)of the strains were grown for 24 h,the sensitivity of the Carba NP test was 84.0%(121/144)and 91.7%(132/144)of the strains were grown for 6h and 12 h,lower than grown for 24 h,but the specificity of the Carba NP test was 96.7%(116/120),no different with the strains were grown for 24 h,the strains stored for 7days yielded positive results for 24 h culture,and the value of Kappa was 0.796,0.878 for the strains were grown for 6h and 12 h,the value of Kappa was 0.796,0.878,0.916 for the strains were grown for 6h,12 h,24h.2 The sensitivity and specificity of the Carba NP test was 95.1%(137/144),95.8%(115/120)of the strains recovered from blood agar,and the value of Kappa was 0.908;the sensitivity of the Carba NP test was 87.5%(126/144),83.3%(120/144)of the strains recovered from MacConkey agar and China Blue agar,and the value of Kappa was 0.810,0.758;the sensitivity and specificity of the Carba NP test was 88.2%(127/144),95.0%(114/120)of the strains recovered from MH agar,and the value of Kappa was 0.826;the sensitivity of the Carba NP test was only 79.9%(115/144)of the strains recovered from Nutrient agar,and the value of Kappa was 0.714;the sensitivity of the Carba NP test was 93.8%(135/144)of the strains recovered from Nutrient agar supplemented with ZnSO4,and the value of Kappa was0.855.3 The sensitivity and specificity of the modified Hodge test was 75.0%(108/144)and 87.5%(105/120),and the value of Kappa was 0.616;the sensitivity and specificity of the Carba NP test was 91.7%(132/144)and97.5%(117/120),and the value of Kappa was 0.886;the sensitivity and specificity of the modified carbapenem inactivation method was 94.5%(136/144)and 97.5%(117/120),and the value of Kappa was 0.916;the sensitivity and specificity of the rapid Carba NP test was 89.6%(129/144)and 99.2%(119/120),and the value of Kappa was 0.879.The date was analyzed by McNemar χ2 test for compare CNP,CIM and RCNP,the ?2 values were 244.58 and 218.51,separately.The P value were both <0.01.4 Underwent mCIM with "0.5 +9 h incubation mode" have a high detection rate for class A,B carbapenemase.The sensitivity and specificity of imCIM was 85.71%(66/77)and 97.86%(183/187),and the value of Kappa was 0.859;the sensitivity and specificity of EDPT was 66.23%(51/77)and88.77%(166/187),and the value of Kappa was 0.561.The difference of inhibition zone of imCIM(ΔdimCIM)was different from EDPT(ΔdEDPT),the difference was statistically significant(P<0.05).The area under the ROC curve of imCIM and EDPT was 0.988(95% CI:0.977~0.999)and 0.936(95%CI:0.909~0.963),respectively.Conclusions:1 The Carba NP test with 6h,12 h culture and stored for 7days yielded positive results for all isolates with positive results for 24 h cultures for class A carbapenemase,incoporation of the test into a single day’s workflow,clearing what the carbapenemase strains produced,but class B and D carbapenemase are more difficult to detect with the Carba NP test.2 Accuracy and rapid of the Carba NP test when carbapenemase-producing strains were recovered on blood agar,the Carba NP test was not suitable to identify carbapenemase producers grown on Mac Conkey agar,China Blue agar,MHagar and Nutrient agar.3 The rapid Carba NP test is more faster than the Carba NP test,by using rub instead of incubation.It can detect the carbapenemaese producers within15 min and contribute to improve nosocomial infection detection efficiency.4 The more simple,rapid,sensitivity,specificity and widely of Carba NP test in detection of carbapenemase-producing strains than modified Hodge test,and it help for identify carbapenemase-producing strains accurately and rapidly.5 The modified carbapenem inactivation method is a low-cost,high efficiency and robust detection method of carbapenemase,it is helpful toimprove the detection rate of carbapenemase-producing strains,and contribute to control the nosocomial infection.6 The establishment of modified carbapenem inactivation method with "0.5 + 9h incubation mode" can provide the basis for early hospital infection control.Compared with EDPT,imCIM is more sensitive and specific to detect class B carbapenemase.The result of imCIM is easy to observe and determine,and the procedure is sample and easy to operate.Thus imCIM is suitable for clinical work. |
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