Hemolytic activity and invasiveness in strains of Proteus penneri.

Twenty strains of Proteus penneri obtained from the Centers for Disease Control, Atlanta, Ga., were tested for their ability to hemolyze sheep and human erythrocytes, a property that is thought to be connected with the invasiveness and virulence of Proteus species. In the logarithmic phase of growth, P. penneri cultures are hemolytic for such erythrocytes. This ability is comparable to the hemolysis exhibited by nearly 100% of P. vulgaris and P. mirabilis strains, which is due to the production of a cell-bound hemolytic factor; is demonstrated only in broth cultures; and seems to facilitate the penetration of P. penneri and other Proteus species into the cells without cytotoxic effects. In contrast, a filterable alpha-hemolysin, which is produced transiently by a very few strains of P. mirabilis, was present in 4 of 20 P. penneri strains. This property, which is expressed at a high level over a long period, suggests a chromosomal origin. The penetration of an alpha-hemolytic P. penneri strain into Vero cells was accompanied by a drastic cytotoxic effect.