OBSERVATIONS ON THE HEMOLYTIC PROPERTIES OF TYPHUS RICKETTSIAE

In 1948 Clarke and Fox reported that crude suspensions of typhus infected yolk sacs caused the lysis of erythrocytes of several animal species in vitro. When it was learned that typhus rickettsiae could be purified by differential centrifugation and treatment with celite in such a way as to reveal their independent metabolic activity (Bovamick and Snyder, 1949) and to preserve their infectivity for cotton rats (Bovarnick et al., 1950), it seemed of interest to determine whether the purified suspensions would still retain the hemolytic properties of the crude tissue supensions. Preliminary tests showed that this was the case, and further experiments with purified rickettsial suspensions have made it posible to detect factors affecting the reaction and to develop a rapid, sensitive hemolysin test. The method as evolved during several years in two different laboratories is based on a 2.5 hour incubation of rickettsiae and red blood cells, followed by colorimetric determination of the hemoglobin released. For convenience this method is referred to subsequently as the "short hemolysin test" to distinguish it from the overnight procedure of Clarke and Fox in which the end point was determined by inspection. This paper describes our standard procedure for the short hemolysin test and its application to quantitation of rickettsial suspensions under various conditions. Experiments on factors affecting the hemolytic activity of typhus rickettsiae are reported.