Outer Membrane Differences between Pathogenic and Environmental Yersinia enterocolitica Biogroups Probed with

Sensitivities to polycationic peptides and EDTA were compared in Yersinia enterocolitica pathogenic and environmental biogroups. As shown by changes in permeability to the fluorescent hydrophobic probe N-phenylnaphthylamine (NPN), the outer membranes (OMs) of pathogenic and environmental strains grown at 26&C in standard broth were more resistant to poly-L-lysine, poly-L-ornithine, melittin, cecropin P1, polymyxin B, and EDTA than Escherichia coli OMs. At 37&C, OMs of pathogenic biogroups were resistant to EDTA and polycations and OMs of environmental strains were resistant to EDTA whereas E. coli OMs were sensitive to both EDTA and polycations. Similar results were found when testing deoxycholate sensitivity after polycation exposure or when isogenic pairs with or without virulence plasmid pYV were compared. With bacteria grown without Ca11 available, OM permeability to NPN was drastically increased in pathogenic but not in environ-mental strains or E. coli. Under these conditions, OMs of pYV1 and pYV2 cells showed small differences in NPN permeability but differences in polycation sensitivity could not be detected by fluorimetry. O:1,6 (envi-ronmental type) lipopolysaccharide (LPS), but not O:3 or O:8 LPS, was markedly rough at 37&C, and this could explain the differences in polycation sensitivity. LPSs from serotypes O:3 and O:8 grown at 37&C were more permeable to NPN than O:1,6 LPS, and O:8 LPS was resistant to polycation-induced permeabilization. These data suggest that LPSs relate to some but not all the OM differences described. It is hypothesized that th