Research On Rapid Detection Of Microorganism In Positive Blood Culture By MALDI-TOF MS And Its Application In Detection AmpC-producing Gram-negative Bacteria

Objective: To evaluate the performance of matrix-assisted laser desorption ionization-time of flight mass spectrometry system(MALDI-TOF)for direct detection of bacteria in the positive bottles by Bac T/ALERT 3D blood culture system and its identification rate.Methods: All positive blood culture bottles reported by Bac T/ALERT 3D blood culture system that had been obtained from the patients in the First Affiliated Hospital of Anhui Medical University from September to November 2016 were selected.The bacteria were directly detected by MALDI-TOF(VITEK-MS)after differential centrifugation,and compared with the results by traditional biochemical identification.Results:Among 150 positive blood culture bottles,there were no bacteria growth in the13 bottles;in the rest 137 bottles,VITEK-MS correctly identified 97(70.8%),wrongly detected 10(7.3%),and could not identify 30(21.9%).For Gram-negative bacteria,the correct identification rate were 61 cases(88.4%)and 8 cases(11.6%)were not identified.In Gram-postive bacteria the correct and wrong identification rate were 36 cases(52.9%)and 10 cases(14.7%),and 22 cases(32.4%)were could not be identified.Conclusion:The method of using VITEK-MS to identify the positive blood culture bottles is accurate and specific.The accurate identification rate of Gram-negative bacteria is much higher than that of Gram-postive bacteria.The time for identification is reduced to 2 hours.Thus,this method can provide rapid and reliable identification of microorganisms in blood culture bottles.Objective: To study the detection of Amp C-producing Gram-negative bacteria by MALDI-TOF MS and to determine whether the method can be used in clinical practice.Methods: A total of 105 strains were detected by determining their phenotypes and sequence analysis.Sixty-nine well-characterized Amp C-producing and 36 non-Amp C producing strains were studied.The bacteria were incubated in different reaction buffer solutions(10m MNH4HCO3/0.005% sodium dodecyl sulphate at p H 8.0)containing cefotaxime(0.50 mg/m L),ceftazidime(0.25 mg/m L),ceftriaxone(0.50 mg/m L),cefepime(0.50 mg/m L),and cefoxitin(0.25 and 0.50 mg/m L),respectively.The mixture was centrifuged at 13,000 g for 2 min,and the supernatant analysed by MALDI-TOF MS after incubation for 30,60,90,120,and 240 min.Antibiotic hydrolysed and decarboxylated peaks were identified.Results:When incubated for 90 min,hydrolysed cefotaxime formed peaks at 434 and494 Da,and the sensitivity and specificity for detection of Amp C-producing strains were85.5%(59/69)and 88.9%(32/36).When incubated for 4 h,hydrolysed ceftazidime formed peaks at 563 and 587 Da,and the sensitivity and specificity were 89.9%(62/69)and 94.5%(34/36),respectively.For hydrolysed ceftriaxone(0.5 mg/m L),cefepime(0.5mg/m L)and two concentrations of cefoxitin(0.25 and 0.5mg/m L),no peaks amenable to analysis were identified.Conclusion:This study demonstrated that MALDI-TOF MS can rapidly detect Amp C producing strains.