OBJECTIVE To evaluate the value of matrix-assisted laser desorption ionization time-of-flight-mass spectrometry(MALDI-TOF MS)in direct identification of carbapenem-resistant Escherichia coli and Klebsiella pneumoniae positive for blood culture.METHODS The blood culture bottles that were positive for E.coli or K.pneumoniae were collected from the patients with bloodstream infection who were treated in Zhongshan Hospi-tal,Fudan University from Jul.2021 to Jun.2023.The isolates were collected by using a gel-contact clotting tube,then the tested strains were respectively mixed with 4 μg/ml of imipenem,4 μg/ml of meropenem and 2 μg/ml of ertapenem for coculture and were incubated at 35 ℃ for 4 and 5 hours,finally,the strains were i-dentified by using the mass spectrum.The minimum inhibitory concentrations(MICs)of the three types of drugs were tested by microbroth dilution method and were set as the golden standards for the test.RESULTS Totally 31 strains of E.coli and 28 strains of K.pneumoniae that were positive in blood culture bottles were collected,both of the effective rates of controlled growth of the E.coli strains were 100.00％after the incuba-tion for 4 and 5 hours,and the effective rates of controlled growth of the K.pneumoniae strains were 9 6.43％and 100.00％after the incubation for 4 and hours,respectively.The sensitivity,specificity,positive predictive value and negative predictive value of the K.pneumoniae strains against the three types of drugs were 100.00％after the incubation for 5 hours.The specificity and positive predictive value of the E.coli strains against imipenem,meropenem and ertapenem were 100.00％after the incubation for 5 hours;the sensitivities were 73.58％,78.93％and 78.93％,respectively;the negative predictive values were 70.60％,75.00％and 75.00％,respectively.CONCLUSIONS MALDI-TOF MS is rapid and accurate for direct identification of the carbapenem-resistant E.coli and K.pneumoniae strains positive in blood culture bottles,and the accuracy reaches at 100.00％for the test of drug-resistant K.pneumoniae strains after the incubation for 5 hours.The method may provide evidence for clinical treatment of bloodstream infections induced by carbapenem-resistant Enterobacteriaceae.

OBJECTIVE To evaluate the value of matrix-assisted laser desorption ionization time-of-flight-mass spectrometry(MALDI-TOF MS)in direct identification of carbapenem-resistant Escherichia coli and Klebsiella pneumoniae positive for blood culture.METHODS The blood culture bottles that were positive for E.coli or K.pneumoniae were collected from the patients with bloodstream infection who were treated in Zhongshan Hospi-tal,Fudan University from Jul.2021 to Jun.2023.The isolates were collected by using a gel-contact clotting tube,then the tested strains were respectively mixed with 4 μg/ml of imipenem,4 μg/ml of meropenem and 2 μg/ml of ertapenem for coculture and were incubated at 35 ℃ for 4 and 5 hours,finally,the strains were i-dentified by using the mass spectrum.The minimum inhibitory concentrations(MICs)of the three types of drugs were tested by microbroth dilution method and were set as the golden standards for the test.RESULTS Totally 31 strains of E.coli and 28 strains of K.pneumoniae that were positive in blood culture bottles were collected,both of the effective rates of controlled growth of the E.coli strains were 100.00％after the incuba-tion for 4 and 5 hours,and the effective rates of controlled growth of the K.pneumoniae strains were 9 6.43％and 100.00％after the incubation for 4 and hours,respectively.The sensitivity,specificity,positive predictive value and negative predictive value of the K.pneumoniae strains against the three types of drugs were 100.00％after the incubation for 5 hours.The specificity and positive predictive value of the E.coli strains against imipenem,meropenem and ertapenem were 100.00％after the incubation for 5 hours;the sensitivities were 73.58％,78.93％and 78.93％,respectively;the negative predictive values were 70.60％,75.00％and 75.00％,respectively.CONCLUSIONS MALDI-TOF MS is rapid and accurate for direct identification of the carbapenem-resistant E.coli and K.pneumoniae strains positive in blood culture bottles,and the accuracy reaches at 100.00％for the test of drug-resistant K.pneumoniae strains after the incubation for 5 hours.The method may provide evidence for clinical treatment of bloodstream infections induced by carbapenem-resistant Enterobacteriaceae.