A CYTOLYSIN ENCODED BY SALMONELLA IS REQUIRED FOR SURVIVAL WITHIN MACROPHAGES

A Salmonella gene encoding a cytolysin has been identified by screenin g for hemolysis on blood agar. DNA sequence analyses together with gen etic mapping in Salmonella suggest that it is unrelated to other toxin s or hemolysins. The gene (slyA) is present in every strain of Salmone lla examined, in Shigella, and in enteroinvasive Escherichia coli but not in other Enterobacteriaceae. SlyA (salmolysin) purified from a der ivative of the original clone has hemolytic and cytolytic activity and has a molecular weight predicted by the DNA sequence. The median leth al dose and infection kinetics in mice suggest that the toxin is requi red for virulence and facilitates Salmonella survival within mouse per itoneal macrophages.