Assay of staphylococcal delta-haemolysin with fish erythrocytes.

Suspensions of erythroctes from certain marine fish (cod, saithe, haddock and mackerel) were 4--16 times more sensitive than human or horse erythrocytes to staphylococcal delta-haemolysin. Cod erythrocytes were lysed rapidly by delta-haemolysin and the titres of haemolysin were independent of the temperatures at which the tests were incubated, over the range 0--37 degrees C. Fish erythrocytes were not lysed by purified alpha- and beta-haemolysins and no synergistic action was found between beta- and delta-haemolysins. In blood agar-overlay plates, the zones of lysis that developed in cod blood agar were larger and clearer than those that developed in human or horse blood agar.