F Pilus as f + Antigen

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Abstract
Specific aggregate formation of F pili was observed, by electron microscopy, in a mixture of male Escherichia coli (or of isolated F pili) and anti-f + serum. Cellular appendages other than F pili never showed such aggregation when mixed with anti-f + serum. The f + agglutinability of male cells, as well as F piliation, was sensitive to mechanical agitation. The f + agglutination was inhibited when appropriate numbers of phage M12, capable of attaching to F pili, were mixed with the male culture before the addition of anti-f + serum. Correlation between f + agglutinability and the extent of F piliation was observed. It was concluded that the F pilus is the structure of the f + antigen and is responsible for f + agglutination.