Cytotoxic activity of supernatant extracts of virulent and saprophytic leptospires.

Extracts from supernatants, obtained from culture of virulent strain PB-3 and saprophytic strain Isola Sacra 1, were assayed for cytotoxicity. A cytotoxic factor produced by the pathogenic strain was found to affect specifically the tested cells, at determined concentrations; on the other side a not clear and scarce cytotoxicity was shown for the extract from the saprophytic strain Isola Sacra 1. Cytotoxic factor produced by strain PB-3 was heat resistant and trypsin sensitive, suggesting to be a thermostable protein. An inhibitory doses it induced a typical, cytopathic effect on the treated cells.