Abstract:

Objective To investigate the feasibility of matrix-assisted laser desorption ionization time-of-flight mass spectrometry（MALDI-TOF MS） in the direct and rapid detection of blood culture positive specimens. Methods Totally,682 positive blood culture specimens were collected from Tongji Hospital. Blood was directly extracted from blood culture bottle and centrifuged in separated gel collecting tube. The centrifugally enriched bacteria were identified by MALDI-TOF MS. They were examined by slide review for the transmitted inoculation culture simultaneously. The culture colonies were identified by Vitek 2 Compact automatic microbial identification system and MALDI-TOF MS. The consistency of the identification results was compared. The strains with different results were verified by 16S rDNA gene sequencing. Results Among 682 blood culture positive specimens,664 cases were infected by single bacterium,and 539 strains（81.2%） were identified by MALDI-TOF MS,122 strains（18.4%） were not identified（species/genus）,but only 3 strains（0.5%） were identified incorrectly（species/genus）,including 1 case of Pantoea,1 case of Klebsiella pneumoniae and 1 case of Staphylococcus capitis. The 664 strains were infected by single bacterium,including 367 strains of Gram-negative bacteria,286 strains of Gram-positive bacteria and 11 strains of Candidia albicans. Compared with the results of traditional colony identification,the accuracies（species/genus） of MALDI-TOF MS were 85.8%/6%,65%/3.1% and 63.6%/0%,respectively. The accuracy of Gram-negative bacteria was higher than those of Gram-positive bacteria and fungi（χ²=57.967,P<0.01;χ²=7.21,P<0.05）. Among Gram-negative bacteria,the accuracies（species/genus） of Enterobacteriaceae,non-fermentative bacteria and other Gram-negative bacteria were 89.0%/5.0%,65.0%/10.0% and 66.7%/22.2%,respectively. Among Gram-positive bacteria,the accuracies（species/genus） of Staphylococcus,Enterococcus,Streptococcus and other Gram-positive bacteria were 70.9%/1.1%,71.4%/2.4%,40.5%/10.8% and 50%/7.1%,respectively. There were 18 cases of complex bacterium infection,of which the accuracy（species/genus） of one or two kinds of bacteria was 77.8% / 0%. Conclusions It is feasible to apply MALDI-TOF MS in direct and rapid detection of positive blood samples,and the accuracy（species/genus） identified monotypic bacteria is high. The accuracy identified common clinical pathogenic bacteria was >70%. The results identified complex bacteria are not good. The rational identification ways should be chosen according to actual situation.

Key words: Matrix-assisted laser desorption ionization time-of-flight mass spectrometry, Direct and rapid detection, Blood culture