The effect of R-plasmid RP1 on the properties of Proteus mirabilis

Abstract

A clinical isolate of Proteus mirabilis containing R-plasmid RP1 (R+ cells), grown in both iron- and carbon- limited chemically defined media in mixed culture with plasmid-free (R- cells), did not disappear as expected, due to adherence of R+ cells to the wall of the chemostat vessel. Plasmid RP1 promoted adherence to glass and to medical prostheses. The hydrophobicity and surface charge of R+ cells were different from those of R- cells and both factors may contribute to the adherence of R+ cells to surfaces. The mode of cultivation of the cells, whether batch or continuous culture, were also found to affect the result. Antibodies raised against homologous cells increased the surface hydrophobicity of both R+ and R- cells and eliminated the differences between them. Results for surface hydrophobicity varied with the method used for measuring it. R+ cells were more sensitive than R- cells to tbe bacteridical action of normal serum and whole blood and to phagocytosis as measured by chemiluminescence. No clear differences were revealed in the protein antigens of R+ and R- cells by both SDS PAGE gels and immunoblots reacted with homologous antibodies. However, lectins revealed differences in the sugars exposed on the cell surfaces. Chemical analysis of R&43 and R- cells also revealed differences in the content of 2-keto-3-deoxy-D-manno-2-octulosonate, lipopolysaccharide and total fatty acids, when cells were grown in media containing added iron; however, no qualitative differences in the lipopolysaccharide were found. Removal of iron from the medium was found to have considerable effects on the chemical structure of R+ cells but not of R- ones. Adhesion to prostheses and to leucocytes is discussed in the light of the results and the clinical relevance outlined with respect to the initiation of infection and the association of virulence with antibiotic resistance.