The MALDI-TOF (Vitek MS, bioMérieux) assay demonstrated accuracy in the rapid identification of the most commonly isolated strains of Enterobacteriaceae, Staphylococcus aureus, and coagulase-negative staphylococci from colonies isolated from positive blood cultures, according to data presented at American Society of Microbiology (ASM) Microbe 2019, held June 20-24 in San Francisco, California.

To test the accuracy of MALDI-TOF identification, positive blood cultures with singular microbes were subcultured onto trypticase-soya sheep blood agar plates in duplicate. After 4 hours of incubation at 350 C in CO2 MS-ID, researchers conducted a triplicate performance of the MALDI-TOF identification. Species or genus identification was accepted if at least 2 of 3 replicates gave the same identification within acceptable thresholds.

A total of 3303 cultures were tested, with 74.4% concordant results (species level 44.9%, genus level 8.3% and coagulase-negative staphylococci group level 23.2%). Of the cultures, 6.4% were mixed and inaccurate occurred identificationin 0.3%. A correct identification of coagulase-negative staphylococci was achieved in 78% of cases with 1 wrong identification.  Results also demonstrated that the percentage of accurate identification of bacterial species was >91% for Escherichia coli (96.5%), S aureus (97.8%), S pneumonia (91.4%), and Klebsiella pneumonia (91.2%); the accuracy for Pseudomonas aeruginosa and the Enterobacter cloacae complex identification were lower at 73.2% and 54.5%, respectively.  

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The investigators concluded that following 4-hour incubation of subcultured positive blood culture vials, rapid and accurate identification with MALDI-TOF is possible for the bacteria tested in the study.

Reference

Ng L, Tan S, Tan T. Accuracy of early identification testing using MALDI TOF on short incubation positive blood culture bacterial colonies. Presented at: ASM Microbe 2019; June 20-24, 2019; San Francisco, California. Poster P519.