A new heat-labile cytolethal distending toxin (CLDT) produced by Escherichia coli isolates from clinical material

Abstract

A new heat-labile Escherichia coli toxin cytolethal to Vero, HeLa, HEp-2 and CHO cells and negative in Y-1 cells has been demonstrated in culture filtrates of 43 E. coli strains associated with diarrheal disease. This new toxin was termed a cytolethal distending toxin (CLDT) to reflect the progressive cell distention and cytotoxicity evidenced in all sensitive tissue cells. CLDT was distinct from the classic heat-labile (LT) and heat-stable enterotoxins, Verotoxins and hemolysins and was produced by some strains of the following E. coli serogroups (02, 07, 08, 018, 022, 039, 044, 055, 083, 086, 091, 0113, 0119, 0128 and 0167). Moderate cyclic AMP accumulation (75-fold) was observed in CHO cells exposed to E. coli CLDT for 24 h. In contrast to E. coli LT, cyclic AMP levels were optimal at 24 h and were observed to decrease over the following 72 h period in CHO cells exposed to E. coli CLDT. In addition to heat-lability at 70 degrees C for 15 min, E. coli CLDT demonstrated a molecular weight over 30,000, was nondialyzable and trypsin-sensitive. E. coli CLDT was negative in adult rabbit ligated ileal loop and suckling mouse assays and provoked only an erythematous response in rabbit skin. All CLDT-positive E. coli strains identified to date were non-hemolytic and non-invasive. Verotoxin and heat-labile enterotoxin were found in combination with CLDT in a few E. coli strains.