Comparing the identification of clostridium SPP. from blood culture using phenotypic, molecular, and two matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry methods: a detailed analysis including the impact of culture age and sample preparation on the peformance on MALDI-TOF systems

Abstract

Introduction We compared the identification of 52 Clostridium species from 52 incident bacteraemic patients using phenotypic analysis, two MALDI-TOF mass spectrometry platforms and molecular sequencing. We also examined the impact of different sample preparations and (on one platform) days of colonial growth on the performance of MALDI-TOF systems. Result 16S rRNA PCR accurately identified 10 Clostridium species amongst the 52 isolates. Combination phenotypic methods identified 44/52 (84.6%) to species level. Spectrometric analysis using Vitek MS yielded 47/52 (90.4%) species using direct transfer (DT), whilst analysis using Bruker MS yielded correct identification dependent on sample preparation [69.2% for DT protocol, 100% for extended direct transfer (EDT) protocol and 100% for full formic extraction (EX) protocol]. Sample preparation didn’t impact the Vitek MS. There was at least moderate agreement in performance for DT, EDT and EX between different days for the Bruker MS. Conclusion Phenotypic identification required numerous methods to accurately identified Clostridium species. Vitek MALDI-TOF MS performed better with the DT protocol compared to the Bruker MS, but the latter yielded correct identification in all samples tested with EDT and EX protocol. Sample preparations did not impact the Vitek MS. On the Bruker MS, the testing cycle can begin upon view of colonial growth.