Partially purified colicin K (mCol K) has been obtained from cultures of Escherichia coli K235 induced with mitomycin C. Unlike colicin K (Col K) derived from noninduced cultures of E. coli K235, mitomycin-induced colicin K (mCol K) is not associated with the type O-specific antigen of the colicinogenic bacillus.

mCol K elicits in rabbits specific antibodies which precipitate and neutralize the homologous bacteriocin. These colicin-specific antibodies are not precipitated by the colicin-O antigen complex derived from noninduced bacteria.

Colicin-neutralizing antibodies can be separated by zone electrophoresis into fractions having different electrophoretic mobilities. The antibodies with lower mobility strongly precipitate the homologous antigen mCol K; those with higher mobility neutralize the bacteriocin and form soluble antigen-antibody complexes.

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