The K antigens of Escherichia coli. Re-examination and re-evaluation of the nature of L antigens.

Re-examination and re-evaluation of three representative Escherichia coli K antigens of the L variety have been carried out (K12, K51 and K52). It is concluded that the K antigen (L) as hitherto described is not uniform, since more K antigen determinants exist on the surface. Some of these are truly thermolabile, probably proteins, while others are thermostable and are eluted into the suspension medium during heating. This elution is rarely complete. The complex character of the K antigens cannot be detected in the traditional bacterial agglutination technique, but can be demonstrated in double diffusion in gel and immuno-electrophoresis and by passive haemagglutination. The implications for K antigen typing are discussed.