In vivo biological characterization of enterotoxins produced by Bacillus cereus strains isolated from milk and milk products

The isolates of 4 most common biotypes under study produced enterotoxin capable of causing Vascular permeability reaction (VPR) and mouse lethality. The VPR zone with 0.05 ml (I/D) of the toxin varied from 11.0 to 29.5 mm. The protein estimation of the toxin revealed that the VPR increased with increase in the concentration of the protein. The isolates B43 and B20 of biotype 6 and 8 produced severe VPR zones of 26.5 mm and 29.5 mm with corresponding necrotic zones of 12.0 mm and 14.5 mm respectively. Almost all the mice died in between 0.5 to 24.0 hr after injecting 0.5 ml toxin (I/P). Toxin with high concentration of protein (5.8 mg/ml) killed mice in 30 min, whereas, at lower protein concentration (2.1 mg/ml) death occurred in 26 hr. Histopathological examination of skin, liver, kidney, heart, intestine and stomach was done to assess the local or systemic tissue reaction of PPDT, which revealed coagulative necrosis of parenchymal cells. Infiltration of neutrophils and mononuclear cells along with oedema and congestion of blood vessels were suggestive of inflammatory response induced by the toxin. Connective tissue fibres showed peculiar eosinophilic gelatinous degeneration. It was postulated that necrotic changes might have been due to trypsin like action of the toxin, whereas, inflammatory changes were due to release of histamine induced by the toxin.