Clinical evaluation of an in-house Xpert Lysate-based Method combined with MALDI-TOF MS for the rapid identification of positive blood cultures.

Abstract

Background: In clinical practice, bloodstream infections (BSIs) can lead to a very high mortality rate. Rapid identification (ID) of the pathogenic bacteria in positive blood cultures (PBCs) can guide the clinical implementation of effective antibiotic treatment in advance, thereby helping to reduce the mortality rate.

Methods: Using the Conventional Culture Method results as criteria, we evaluated the effectiveness of our newly developed in-house method, the Xpert Lysate-based Method, for rapidly identifying pathogens in PBCs across four hospitals.

Results: A total of 629 monomicrobial PBCs were investigated. The Xpert Lysate-based Method correctly identified 96.18% of PBCs at the species level and 97.30% at the genus level. When the confidence scores of MALDI-TOF MS were ≥ 2.000, ≥ 1.700, and ≥ 1.500, the percentages of correctly identified PBCs at the species level were 67.47%, 94.24%, and 98.88%, respectively. When the score threshold of species-level ID was set to 1.500, the rates reached 98.25% for Gram-positives (GPs), 93.54% for Gram-negatives (GNs), 70.00% for anaerobes, and 94.74% for fungi, respectively. The median confidence score of ≥ 2.000 indicated high certainty in identifying common BSI pathogens. Additionally, one of the microbial species was correctly identified in 10 out of 11 PBCs with polymicrobial growth. The entire operation process took an average of 10 min of hands-on time and 15 to 20 min for time-to-result.

Conclusion: The method of directly identifying microbial pellets using MALDI-TOF MS, extracted via the Xpert Lysate-based Method we developed, is non-inferior to the conventional Culture Method in terms of ID performance. Meanwhile, it is easy to operate and more time-efficient, making it suitable for routine workflow in the rapid etiological ID of PBCs.