Haemolytic activity and characteristics of plasmid and chromosomally borne hly genes isolated from E. coli of different origin.

20 hly plasmids of different origin and source and 8 recombinant plasmids containing either chromosomally or plasmid encoded hly determinants were characterized with emphasis on their haemolytic activity. Remarkable differences among the hly genes tested were found in their haemolytic activity and in the regulation of the haemolytic activity by the extracellular iron concentration. Under iron-limiting growth conditions the haemolysin secretion encoded by 6 hly plasmids, but not by the remaining 14 hly plasmids and the chromosomal hly genes, was significantly induced. The 6 plasmids all derived from human isolates, belonged to the incompatibility groups FIV and FVI and showed similar restriction patterns. Two hly determinants, encoding an inducible haemolysin secretion, cloned from plasmids isolated in Berne and Paris, respectively, showed identical restriction maps, indicating a common origin. Compared to the hly determinant of a plasmid encoding a noninducible haemolysin secretion, distinct differences, mainly in the flanking regions, were observed.