Isolation and characterisation of four distinct cytotoxic factors of Salmonella Weltevreden B R Singh & V.D. Sharma Department of Veterinary Microbiology College of Veterinary Sciences G B Pant University of Agriculture & Technology Pantnagar-263 145, India Four distinct cytotoxins with different biological, physico-chemical and antigenic characteristics were isolated from a single Salmonella Weltevreden strain recovered from buffalo meat. The toxins were purified through salt precipitation, dialysis, gel filtration and ion-exchange chromatographic methods. Cytotoxin I was dermonecrotic, verocytotoxic and lethal to mouse with 120 μg LD 50 . It induced accumulation of serosanguinous fluid in rabbit ligated ileal loop (RLIL) and mucinous fluid in the stomach. It was active within a narrow pH range (5.0 - 8.0) and lost its activity on autoclaving for 1 min. Cytotoxin II was verocytotoxic, enterotoxic and lethal to mouse (LD 50 , 1 mg). It induced delayed vasopermeability in rabbit skin, was active between pH 5.6 and 8.4 only and heat- sensitive (100°C, 30 min). Cytotoxin III was neither dermatotoxic nor enterotoxic. It induced vacuolation, multinucleation and formation of syncytia in vero cells. It was sensitive to pH beyond the range of 4.8 to 8.2. It was completely inactivated on boiling for 30 min. Cytotoxin IV was intensely necrotizing to rabbit skin within 6 h of inoculation and lysed Vero cells. It also possessed haemolytic and lecithinase/phospholipase-C activities. The cytotoxin lost its activity on heating at 90°C (30 min) but remained active between pH 2.5 and 7.5. The PIs of the cytotoxins were estimated to be 9.0, 7.0, 5.6 and 3.0, respectively. All the four cytotoxins were immunogenic in rabbits but antigenically unrelated as the anticytotoxin neutralized only the homologous cytotoxin and did not cross react with heterologous cytotoxins. * Present address: Scientist, National Salmonella Centre (Vet), Division of Bacteriology and Mycology, Indian Veterinary Research Institute, Izatnagar-243 122 (UP), India. PDF created with pdfFactory Pro trial version www.pdffactory.com