Rapid and cost-effective identification of microorganisms from positive blood cultures using MALDI-TOF MS

Rapid and accurate pathogen identification is critical and has a major impact on sepsis-related mortality and morbidity rates. The aim of this study is to evaluate the performance of a simple, fast, and inexpensive method for direct processing of positive blood cultures for immediate identification of microorganisms using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS).

This study was performed on 125 positive blood culture bottles collected from April 2022 to September 2023. We compared using MALDI-TOF MS for identifying isolated microorganisms from positive blood culture bottles on routine culture media versus identifying microorganisms directly from positive blood culture bottles without previous isolation on routine culture media.

The total number of microorganisms isolated by routine subculture methods was 128, as three bottles had two types of organisms. Out of the 128 organisms isolated by routine subculture method, 97 (75.8%) organisms were identified to species level using the direct detection method from blood culture bottles by MALDI-TOF MS. 4 (3.1%) organisms were identified to genus level only, while 3 (2.3%) were wrongly identified. This direct method could not identify 24 (18.8%) organisms. Gram-negative organisms were identified with high accuracy, achieving 90.16% (55/61) at the species level and 3.28% (2/61) at the genus level. Among Gram-positive organisms, 69.1% (38/55) were identified to the species level, while 27.3% (15/55) could not be identified. Yeast identification was limited, with only 33.3% (4/12) identified to the species level, 8.3% (1/12) to the genus level, and 41.7% (5/12) could not be identified.

This method showed great sensitivity for the identification of Gram-negative bacteria, directly from positive blood culture bottles, followed by Gram-positive bacteria, and very low sensitivity for yeasts.