Evaluation And Application Of The Improved Chromogenic Medium For Screening CRE

ObjectivesThis study was conducted to prepare the improved chromogenic medium for rapid screening of CRE and evaluate its performance;to determine the prevalence of intestinal colonization by CRE and to identify the risk factors associated with intestinal CRE colonization among ICU patients;providing a laboratory evidence for the prevention and control of CRE infection as well as the guidance of clinical treament.MethodsThe 49 strains of CRE and 24 strains of non-CRE isolated from clinical specimens were evaluated for the performance of the three types of improved chromogenic medium containing imipenem at 2?g/ml,meropenem at 2?g/ml,and ertapenem at 2?g/ml respectively;Furthermore,a total of 191 stool specimens collected from ICU patients in our hospital were uesd to evaluate the performance of four different methods of CRE screening including the CDC broth method,CHROMagar KPC,MacConkey plates?plus ertapenem disks?,and the ertapenem-improved chromogenic medium.Using the ertapenem-improved chromogenic medium to actively screen CRE for stool samples from ICU patients between March 2018 and August 2018.The strain identification and antimicrobial susceptibility testing were performed by using MALDI-TOF MS and Vitek 2 Compact system,respectively.The carbapenemase of all isolates was determined by phenotype and genotypes.Clonal relatedness was analyzed by pulsed-field gel electrophoresis?PFGE?.In addition,the clinical data of the patients were collected,and logistic regression analysis was used to determine the independent risk factors responsible for CRE colonization.ResultsThe sensitivity and specificity of the imipenem-improved chromogenic medium were83.7%and 100.0%,respectively;the sensitivity and specificity of the meropenem-improved chromogenic medium were 87.8%and 100.0%,respectively;the sensitivity and specificity of ertapenem-improved chromogenic medium were 93.9%and 95.8%,respectively.There was no significant difference in sensitivity and specificity between the three improved chromogenic medium?P>0.05?.The area under the ROC curve of the ertapenem-modified chromogenic medium was 0.949,the imipenem-modified chromogenic medium was 0.918,and the meropenem-improved chromogenic medium was 0.939.The sensitivity and specificity of the CDC broth method were 80.3%and 79.2%,respectively;the sensitivity and specificity of CHROMagar KPC were 93.4%and 97.7%,respectively;the sensitivity and specificity of MacConkey plates?plus ertapenem disks?were 80.3%and 96.9%,respectively;the sensitivity and specificity of the ertapenem-improved chromogenic medium were 98.4%and 98.5%,respectively?evaluation by using stool samples?.The sensitivity of the ertapenem-modified chromogenic medium was higher than the CDC broth method and MacConkey plates?plus ertapenem disks??P<0.05?;The sensitivity of CHROMagar KPC was higher than the CDC broth method and MacConkey plates?plus ertapenem disks??P<0.05?;There was no statistical significance in sensitivity between the ertapenem-modified chromogenic plate and CHROMagar KPC?P>0.05?;There was no statistical significance in sensitivity between the MacConkey plates?plus ertapenem disks?and the CDC broth method?P>0.05?.The specificity of the ertapenem-modified chromogenic medium was higher than that of the CDC broth method?P<0.05?.There was no statistical significance between the ertapenem-modified chromogenic medium,CHROMagar KPC and MacConkey plates?plus ertapenem disks??P>0.05?.The specificity of CHROMagar KPC was higher than the CDC broth method?P<0.05?,but the difference between the MacConkey plates?plus ertapenem disks?was not statistically significant?P>0.05?;The specificity of the MacConkey plates?plus ertapenem disks?was higher than the CDC broth method?P<0.05?.The area under the ROC curve of the CDC broth method,CHROMagar KPC,the MacConkey plates?plus ertapenem disks?,and the ertapenem-modified chromogenic medium were 0.798,0.956,0.886,and 0.984,respectively.During the period from March 2018 to August 2018,the overall colonization rate of CRE in the intestine of ICU patients was 40.4%?82/203?.84 strains of CRE were isolated from 82 patients,including 78 isolates of Klebsiella pneumoniae?92.9%?,4isolates of Escherichia coli?4.9%?,1 isolate of Enterobacter cloacae?1.2%?,and 1isolate of Citrobacter freumdii?1.2%?.84 strains of CRE showed high resistance to most antibiotics.The resistance rate of antibiotics was higher than 90%except gentamicin,tobramycin,amikacin,and aztreonam.There were 75 isolates positive detected by mCIM;76 isolates harbored carbapenemase genes including bla_KPC-2,bla_NDM-1,and bla_IMP-4.68 isolates harbored bla_KPC-2,7 isolates harbored bla_NDM-1,and 1isolate co-harbored bla_KPC-2,bla_NDM-1 and bla_IMP-4.PFGE analysis showed seventy-eight isolates of Klebsiella pneumoniae were divided into eight pulsotypes marked as A?51/78,65.4%?,B?12/78,15.4%?,C?6/78,7.7%?,D?3/78,3.8%?,E?2/78,2.6%?,F?2/78,2.6%?,G?1/78,1.3%?,and H?1/78,1.3%?.Logistic regression analysis showed invasive procedures?OR:3.282;95%CI:1.159-9.291?,cerebrovascular disease?OR:2.521;95%CI:1.257-5.056?and lung disease?OR:2.007;95%CI:1.074-3.750?were independent risk factors responsible for CRE colonization.ConclutionsThe ertapenem-improved chromogenic medium not only had great sensitivity and specificity,but also had the advantages of shorter screening period,lower price,convenience,etc.It is more suitable for the application of clinical microbiology laboratory.Our study showed an alarmingly high prevalence of CRE colonization among ICU patients,and the strain of CRE was mainly Klebsiella pneumoniae.The main resistance mechanism was producing KPC-2 enzyme.These strains showed resistance to various antibiotics.Invasive procedures,cerebrovascular diseases and lung diseases were significant risk factors for CRE colonization;The transmission of carbapenem-resistant Klebsiella pneumoniae from patient to patient may occur.Thus,the clinicians as well as the departments of infection prevention and control should take some effective measures to prevent further spread of CRE.