The strains selected here for study were identified previously as
members of the genus Micrococcus (using fermentation tests and
direct MALDI TOF profiles), but their species identification was less
certain. MALDI TOF MS profiling identified all 22 isolates as
M. luteus. However, two of the strains (ASO3-C10 and ASO3-C17)
were weakly positive for metabolism of glucose, which is inconsistent
with the known characteristics of M. luteus. The identification
scores of these strains were in the range of “secure genus
identification and probable species identification” according to the
Bruker Biotyper software and reference library (Bruker Daltonics,
Bremen, Germany), which contains more than 3200 entries. The
assigned scores ranged from 2.00 to 2.299. All of the strains fell
within this scoring category. The MALDI TOF MS profiles were
compared with data available in a database of reference strains, in
order to determine the identification of unknown samples. When
the work was performed (2009e2010), the Bruker database contained
only one reference of M. luteus ATCC 4698 [6].