Sample preparation and further proteomic investigation of the inhibitory activity of pyridinium oximes to Gram-positive and Gram-negative food pathogens

The antimicrobial activity of quaternary ammonium salts of pyridinium oxime against four food pathogenic bacteria, the Gram positive Bacillus subtilis and Listeria monocytogenes, as well as the Gram negative Escherichia coli and Yersinia enterocolitica, were evaluated. Changes of proteome in these bacteria grown under stress conditions were identified. By the application of a new method for sample preparation, followed by both in-gel and in-solution digestion and LC–MS/MS, both characterization and comparison of proteomes of these food pathogens were achieved. It was shown in all investigated bacteria that some of the proteins of key importance for protein turnover and bacterial metabolism are down regulated. Some stress proteins involved in protein folding and degradation were up regulated. Most of both up- and down-regulated proteins belong to the group of proteins with high abundance. Flagellin is the only protein of lower abundance that was found to be down regulated in two strains, B. subtilis and E. coli. The presented results give the better view into the proteome of food pathogens, and pave the way for further investigation of their virulence, pathogenicity and detection of biomarkers for tracing the ways and sources of food contamination.