Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry
accurately identifies both selected bacteria and bacteria in select clinical situations.
It has not been evaluated for routine use in the clinic.
We prospectively analyzed routine MALDI-TOF mass spectrometry identification in parallel
with conventional phenotypic identification of bacteria regardless of phylum or source
of isolation. Discrepancies were resolved by 16S ribosomal RNA and rpoB gene sequence-based
molecular identification. Colonies (4 spots per isolate directly deposited on the
MALDI-TOF plate) were analyzed using an Autoflex II Bruker Daltonik mass spectrometer.
Peptidic spectra were compared with the Bruker BioTyper database, version 2.0, and
the identification score was noted. Delays and costs of identification were measured.
Of 1660 bacterial isolates analyzed, 95.4% were correctly identified by MALDI-TOF
mass spectrometry; 84.1% were identified at the species level, and 11.3% were identified
at the genus level. In most cases, absence of identification (2.8% of isolates) and
erroneous identification (1.7% of isolates) were due to improper database entries.
Accurate MALDI-TOF mass spectrometry identification was significantly correlated with
having 10 reference spectra in the database (P=.01). The mean time required for MALDI-TOF
mass spectrometry identification of 1 isolate was 6 minutes for an estimated 22%-32%
cost of current methods of identification.
MALDI-TOF mass spectrometry is a cost-effective, accurate method for routine identification
of bacterial isolates in <1 h using a database comprising > or =10 reference spectra
per bacterial species and a 1.9 identification score (Brucker system). It may replace
Gram staining and biochemical identification in the near future.