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.