Mechanisms of resistance in Salmonella enterica

The aim of this study was to promote resistance in Salmonella enterica serovar Enteritidis, Typhimurium, and Virchow to commonly used antibacterials and to identify mechanisms underlying any resistance obtained. Strains were exposed to various biocides and following each passage adaptive resistance was recorded. Permeability changes in the outer membrane, including LPS, cell surface charge and hydrophobicity and efflux were investigated as possible resistance mechanism candidates. The outer membrane and LPS bands were analysed by SDS-PAGE and visualised by Coomassie blue and silver staining. The cell surface charge and hydrophobicity were investigated employing microelectrophoresis and microbial adhesion to hydrocarbons assay, respectively. Efflux activity was examined by comparing resistance in preand post-adapted strains in the presence of reserpine. The outer membrane and LPS did not reveal any significant changes. Most of the parent strains were not significantly hydrophobic, whereas adapted were. An active efflux system was associated with benzalkonium chloride and chlorohexidine resistance.