Microbial organisms populate all orifices and surfaces of many organs in the body, and their proteins may enter the blood intact or after degradation, as well as through contamination during venepuncture. We separately matched our peak lists for six small datasets against microbial genomes in the NCBI Microbial (nonhuman) GenBank (June 2004 release), using X!Tandem for RefSeq protein sequence identification. In this preliminary analysis, we found matches to several E. coli proteins (including elongation factor EF-Tu, outer membrane protein 3a, and glutamate decarboxylase isozyme) and mycobacterial proteins (members of glycine-rich PE-PGRS family) based on at least three peptide matches. No peptides for these proteins were found in the IPI human database, so these sequences are independent of the human gene and protein collections.
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