The somatic antigen of the non-colicinogenic bacillus E. coli K235 L-OC- has been isolated, and its chemical and serological properties have been compared with those of colicine K. The antigen of the non-colicinogenic bacillus has a protein content significantly lower than that of the C+ antigen, a difference which might be related to the antibacterial activity of the latter.

The lipocarbohydrate components of the two antigens are chemically very similar; both contain the same proportions of galactose, glucose, heptose, rhamnose, glucosamine, and mannosamine.

When tested by agar diffusion, the two antigens are indistinguishable, as are their lipocarbohydrate components.

Our studies indicate that the bactericidal activity of colicine K does not reside in its lipocarbohydrate but in its protein component.

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