A plasmid-mediated surface antigen of naturally occurring strains of escherichia coli.

A plasmid-mediated surface antigen of naturally occurring Escherichia coli strains were demonstrated. This antigen was classified into L type (heat-labile K) antigens but was suggested not to be a pilus antigen, because no pilus was found on the surface of those common pili-free E. coli C strains carrying the responsible plasmids and also because the strains did not hemag-glutinate red blood cells of any animal species so far studied. Incidences of such antigen-forming strains were higher in the strains isolated from feces and respiratory tract secretions than in those from other sources. Plasmid DNAs from these strains were different from one another in their molecular sizes, but they had a common size band after digestion by EcoRI endonuclease, suggesting that they had a similar or the same origin(s).