Applied Research Of MALDI-TOF MS In Direct Determination Of Microorganisms From Positive Blood Cultures And Rapid Detection Of Carbapenem Resistance

OBJECTIVE To apply matrix assisted laser desorption ionization time of flight mass spectrometry(MALDI-TOF MS)in direct identification of microorganisms from positive blood cultures,and on that basis carry on direct antimicrobial susceptibility tests of common bacteria from blood cultures,and provide basis for reasonable and rapid blood infection treatment in clinic.To apply MALDI-TOF MS for rapid detection of ertapenem hydrolysis capacity of carbapenems resistance Enterobacteriaceae(CRE),and provide a new way of rapid detection of the resistance for Enterobacteriaceae.METHODS 1.MALDI Sepsityper? Kit combined with MALDI-TOF MS(MSK-MS)and separation gel combined with MALDI-TOF MS(SG-MS)were utilized to directly identify microorganisms in 491 cases of positive blood cultures.Meanwhile positive blood cultures were routinely cultured for microorganisms identification(Routine identification).The identifications resluts that were inconsistent between direct and routine method were confirmed by gene sequencing.2.Based on the identification results of SG-MS method,four antimicrobial susceptibility tests(direct K-B,routine K-B,direct MIC and routine MIC)of 236 strians of common bacteria from blood cultures were performed The results of direct and routine antimicrobial susceptibility tests were compared,respectively.3.MALDI-TOF MS was applied to the ertapenem hydrolysis tests for 108 strains of CRE and 9 strains of carbapenem-susceptible Enterobacteriaceae.RESULTS 1.Compared with routine identification results(or gene sequencing results),the identification results of direct MSK-MS method indicated that the "species" identification coincidence rates,"genus" identification coincidence rates,unidentified rates and error rates of 462 strains of monomicrobial blood cultures were 72.5%,76.0%,23.6% and 0.4%,respectively.And the "species" coincidence rates of common bacteria from blood cultures were 71.0%~92.9%.In 29 cases of polymicrobial blood cultures,both types of bacteria could be identified in 7 cases,and one types of bacteria could be identified in 15 cases,and neither types of bacteria could be identified in 7 cases.The identification time of MSK-MS method was about 40 minutes/specimen.Compared with routine identification results(or gene sequencing results),the identification results of direct SG-MS method indicated that the "species" identification coincidence rates,"genus" identification coincidence rates,unidentified rates and error rates of 462 strains of monomicrobial blood cultures were 73.6%,77.3%,22.5% and 0.2%,respectively.And the "species" coincidence rates of common bacteria from blood cultures were 78.6%~96.9%.In 29 cases of polymicrobial blood cultures,both types of bacteria could be identified in 4 cases,and one types of bacteria was identified in 18 cases,and neither types of bacteria was identified in 6 cases,and the identification result of 1 cases was incorrect.The identification time of SG-MS method was about 40 minutes/specimen.2.Compared with K-B routine antimicrobial susceptibility tests results,the coincidence rates,minor error rates and major error rates of K-B direct antimicrobial susceptibility tests results of gram negative rods were 97.8%,1.4% and 0.8%,respectively,and the rates of gram positive cocci were 98.5%,0.9% and 0.6%,respectively.Compared with MIC routine antimicrobial susceptibility tests results,the coincidence rates,minor error rates and major error rates of MIC direct antimicrobial susceptibility tests results of gram negative rods were 98.0%,1.1% and 0.9%,respectively,and the rates of gram positive cocci were 98.4%,0.9% and 0.7%,respectively.Beginning with alarm time of positive blood cultures,it was about 24 hours to obtain the results of direct antimicrobial susceptibility tests.3.MALDI-TOF MS ertapenem hydrolysis tests results of 102 strains of carbapenemases-producing CRE were all positive,and the results of 6 strains of carbapenemases-noproducing CRE and 9 strains of carbapenem-susceptible Enterobacteriaceae were all negative,and the tests took about 2 hours.CONCLUSION MALDI-TOF MS can not only be used to directly determine microorganisms from positive blood cultures,it also can be used to rapidly detect carbapenem resistance of Enterobacteriaceae.It has the advantage of fast,accurate,economical,effective and so on,which is worthy of wide application in clinical microbiology laboratories.