Comparison of two matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry methods and API 20AN for identification of clinically relevant anaerobic bacteria

Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) is suitable for high-throughput and rapid microbial diagnosis at relatively low cost and can be considered an alternative to conventional biochemical and molecular identification systems in clinical microbiological laboratories, including anaerobe laboratories. Two commercially available MALDI-TOF MS systems, Bruker Microflex MS and bioMerieux VITEK MS, were evaluated for the identification of 274 isolates of clinically significant anaerobic bacteria recovered from routine cultures of clinical specimens in parallel with blinded comparison with conventional biochemical (API 20AN) or molecular methods. All were recovered cultures obtained from patients attending the Mubarak Al Kabir Hospital, Kuwait, during a 6 month period. Discrepant results after two attempts at direct colony testing had failed to provide acceptable MALDI-TOF identification were resolved by gold-standard 16S gene sequencing. The VITEK MS gave high-confidence identification of the 274 isolates, all of which were correctly identified. The Bruker Microflex MS system also gave high-confidence identification for 272 of the 274. After discrepancy testing, the Bruker MS results agreed with biochemical or molecular methods for 89.1% of the isolates at species level and 10.2% at genus level (0.72% were misidentified). The level of agreement with the VITEK MS was 100% at both species and genus level; no isolates were misidentified. Our data suggest that implementation of MALDI-TOF MS as a first step for identification will shorten the turnaround time and reduce the cost in the anaerobe laboratory.