The w100 kDa-bands detected in all individual environmental
isolates and reference strains were digested with trypsin and the
mass spectra of tryptic peptides were compared to evaluate similarities
and differences. MALDI TOF MS peptide profiles verified
that all of the environmental strains had similar mass spectra for
this protein, with an abundant and unique peptide being located
at 1840.9 m/z (see Fig. 1). Using the NCBI database within the
MASCOT search engine, commonly used for identifying proteins
based on mass spectral data, the w100 kDa protein was identified
as aconitate hydratase. Each environmental isolate was analyzed
a minimum of twice, followed by processing the data using
MASCOT. In total, 75 MALDI TOF MS analyses were subjected to
MASCOT searches on the 22 environmental isolates. Although the
spectra were remarkably similar, only 3 of the 75 mass spectra were
identified as aconitate hydratase with a MOWSE score, but the
valuewas less than the identification confidence level. Previously, it
was noted that MASCOT only identified aconitate hydratase in some
of the environmentally isolated staphylococcal strains [6], consistent
with the results presented here for Micrococcus.