Rapid Identification And Drug Sensitivity Test Of Bloodstream Infected Pathogens Based On MALDI-TOF MS

Matrix-assisted laser desorption/Ionization Time-of-flight Mass Spectrometry(MALDI-TOF MS)offers an effective approach to rapid and reliable identification of bacteria.The MALDI-TOF MS instruments used in the clinical microbiology laboratory are usually importing equipment.The domestic mass spectrometer has developed rapidly in recent years,however,it only allows to identify the bacteria at the species level based on their protein profiles from the single colony of cells,and there is no data on direct identification of bacteria from clinical samples.Bloodstream infection,especially caused by multi-drug resistant strains,is one of the most serious infections in clinical with high morbidity and mortality.Therefore,direct,rapid and accurate identification of pathogens from positive blood cultures is the key to the clinical diagnosis and effective treatment.The current study is divided into two parts.The first part is to apply the improved method to evaluating the feasibility of direct identification of pathogens from positive blood cultures by domestic mass spectrometer(Yixin Bochuang Clin-TOF-II MS),to provide data support for the domestic mass spectrometer into clinical laboratory.The second part is to directly identify the carbapenem-resistant Enterobacteriaceae strains from the positive blood cultures by the German Bruker mass spectrometer(Microflex LT Bruker MS),aiming to shorten the turn-around time,reduce the costs and help provide clinical effective treatment.The first part: to apply the improved method to evaluating the feasibility of direct identification of pathogens from positive blood cultures by Clin-TOF-II MS.A total of666 bottles of positive blood cultures were collected and identified the microorganisms by Clin-TOF-II MS after sample pretreatment,including 97 BD BACTEC's Plus Aerobic/F(PAF)bottles,121 BACTEC's Lytic Anaerobic/F(LAF),161 BacT/Alert FAN Aerobic bottles(FA),197 BacT/Alert FAN Anaerobic Plus(FN),90 Standard Aerobic(SA).The identification results based on the pure cultures byBruker MS were used as reference.The accuracy of Clin-TOF-II MS for positive blood cultures was up to 88.6%(590/666).The second part: to directly identify the carbapenem-resistant Enterobacteriaceae strains from the positive blood cultures by Bruker MS.A total of 50 carbapenem resistant Klebsiella pneumoniae strains and a Klebsiella pneumoniae ATCC700603 strain were selected as the simulators to obtain the characteristic peaks of intact and hydrolyzed meropenem for distinguishing the carbapenamase-producing Enterobacteriaceae strains.Among 106 clinical positive blood cultures,105 blood culture samples were successfully identified and the one was misidentified for the mixed bacterial infection.Of the 105 samples,94 were identified as Enterobacteriaceae strains,and then were carried out meropenem hydrolysis assay by Bruker MS.The accuracy of differentiating carbapenem resistant Enterobacteriaceae was 92.6%(87/94),The sensitivity was 84.2%(32/38)and the specificity was 100%(55/55).Our study showed that our improved methods have a good advantage in rapid identification of positive blood samples by the domestic mass spectrometer and in differentiating carbapenem-resistant Enterobacteriaceae strains rapidly from positive blood samples by Bruker MS,which shortens the turn-around time,helps clinicians develop effective treatment strategies,and ensures the rational use of antibiotics.