Temperature-dependent flagellar antigen phase variation in Escherichia coli.

A new kind of flagellar phase (H antigen) variation which is dependent on the temperature of growth is described for Escherichia coli strains, all but one of which belong to serogroup O148, isolated in different geographical regions. At 37 degrees C the strains simultaneously displayed two different H antigen specificities, H40 and H53, while in cultures grown at 30 degrees C only a single flagellar antigen, H53, was detected. It was shown that the bacteria possess two separate flagellin genes, fliC40 and flkA53. An element controlling the temperature-dependent expression of fliC was localized in the region of flkA53. Relevant problems in H antigen serotyping in E. coli are discussed.