Comparison of a Sepsityper® kit and in-house membrane filtration methods for rapidly diagnosing positive blood cultures via MALDI‒TOF MS.

Background: Rapidly identifying pathogens and determining their antimicrobial susceptibilities using samples directly from flagged blood culture bottles pose significant challenges for clinical laboratories. Thus, a cost-effective and efficient sample-processing method is urgently needed to address this issue. To fulfill this need, we developed a novel protocol to rapidly identify pathogens and determine their antimicrobial susceptibilities using samples directly from blood culture bottles.

Methods: Samples were either processed by the Sepsityper kit or our in-house methods. In our approach, we processed the samples using either a nonionic surfactant (Triton X-100) or a NaOH-sodium dodecyl sulfate (SDS) solution, followed by membrane filtration (MF) and centrifugation. Subsequently, the samples were analyzed using MALDI-TOF mass spectrometry (MS) for identification and the Vitek® 2 for antimicrobial susceptibility determination.

Results: In this study, 122 clinical blood culture samples were analyzed, and our MF protocol displayed enhanced accuracy in identifying gram-positive organisms (n = 58) and gram-negative bacilli (n = 64) compared to the Sepsityper method. In particular, the Triton-MF and SDS-MF techniques outperformed Sepsityper in identifying gram-negative bacilli, with accuracy rates of 92.2 %, 85.9 %, and 78.1 %, respectively. Notably, both the Triton-MF and SDS-MF methods exhibited high categorical agreement (CA) for antimicrobial susceptibility testing (AST) for carbapenem against Enterobacterales, with CAs of 100 % and 98.7 %, respectively. Additionally, both methods exhibited a perfect CA and essential agreement of 100 % for Enterococcus faecium AST for vancomycin.

Conclusion: These findings strongly indicate that our MF methods have the potential to streamline the identification and AST of bacteria in positive blood cultures.