The production of HlyA toxin by Proteus penneri strains.

Twelve diverse strains of Proteus penneri of clinical origin all produced a calcium-dependent haemolysin, unlike most other Proteus spp. In most strains the haemolysin was secreted into the medium during early exponential growth and lysed not only of a variety of erythrocyte types from several animals including man, but also human neutrophils and human embryo lung fibroblasts. The haemolysin was a protein of 107 kDa, the same size as Escherichia coli HlyA, and it reacted with antiserum to E. coli HlyA. Because of its similarity in size, antigenicity and range of action to the HlyA virulence factor of E. coli, P. penneri HlyA is believed to be an important virulence factor for this organism. It was degradable by an EDTA-sensitive protease--probably the IgA protease--to inactive fragments. The interaction of P. penneri HlyA and IgA protease in vivo and the origin of HlyA, which has now been found in many diverse bacteria, are discussed.