Investigation of the haemolytic activity of Proteus mirabilis strains.

Young broth cultures of all P. mirabilis strains tested exhibited haemolytic activity. This activity seemed to be strongly cell-associated as only a very small fraction of this activity was found in the cell-free supernatant. The haemolysin was only produced by actively growing cells. Inhibition studies with trypsin and chloramphenicol suggested that the haemolysin is of protein nature. Lecithin and serum of several species had an inhibitory effect on the haemolysin. Besides erythrocytes of various species also VERO cells were affected by the haemolysin. A correlation was found between the haemolytic activity of a strain and its virulence in an experimental mouse model.