Characterization of cytotoxic factors of Yersinia pseudotuberculosis using the MDBK cell line

The cytotoxin of four strains of Yersinia pseudotuberculosis was characterized using the MDBK cell line and by application of the MTT colorimetric test. The highest cytotoxin yield was obtained in tryptic soy broth medium after 24 h. It was detected in the cell-free culture filtrate, and treatment of the cells with CHAPS as a membrane detergent did not decrease significantly their cytotoxic activity. The cytotoxin was inhibited by trypsinization and by increasing values of either acidity or alkalinity. The cytotoxin was inactivated partially by heating at 70 degrees C for 20 min and totally at 90 degrees C for 10 min. The results obtained indicate that the cytotoxin is protein in nature and produced mainly as free exotoxin.