Identification and secretion of the E.coli haemolysin.

Haemolysin is secreted into the medium by many pathogenic E. coli strains. In this study haemolytic activity was detected either by growth of the bacteria on blood agar or by adding culture supernatants to a bioassay containing fresh sheep blood. Levels of haemolytic activity in the latter case appeared to be dependent upon the growth medium. The haemolysin itself was tentatively identified as a 107K polypeptide both by partial protein purification and by a genetical analysis. A similar protein was secreted by a variety of haemolytic E.coli strains isolated from both animals and humans. Analysis of the haemolysin determinant of pHlyl67 revealed some strong similarities to the gene organization of pHlyl52 previously reported by Noegel et al. (1979). Finally, the haemolysin genes from a human E.coli isolate, LE2001, were successfully cloned and mapped in detail using transpositional mutagenesis. Haemolysin specific genes were located within a minimum region of 7-kb which could be divided into information coding for structural and export functions. The possible roles of the additional proteins are discussed.