Surface antigens of Proteus mirabilis revealed by electroblotting from sodium dodecyl sulphate-polyacrylamide gels

Western Blotting of whole cell preparations of three strains of Proteus mirabilis after separation by electrophoresis on SDS-polyacrylamide gels revealed a complex pattern of antigens. Similar antigen profiles were obtained with isolated outer membranes indicating that the majority of cell surface antigens are located in the outer membrane. Major outer membrane proteins were strongly antigenic and cross-reactive. The highly immunogenic flagella were detected in whole cell preparations and visible in isolated outer membranes. Whereas the protein and flagellar antigens were cross-reactive, lipopolysaccharide (LPS) could only be detected as immunoreactive material using homologous antisera for each strain. The LPS appeared as two broad bands (high and low Mr, respectively) in immunoblots of whole cells, isolated outer membranes and purified LPS. However, isolated LPS could be resolved into multiple sharp bands when 4 M urea was included in the gel system. These discrete bands are assumed to represent differing O antigen chain lengths of the LPS as reported for other Gram-negative organisms.