Samples of 124 different foods purchased from local markets were examined to determine the incidence of Bacillus cereus. The foods examined were pulses, rice and rice products, oils, fish, meat, spices, milk and milk products and ice creams. Isolations were made on mannitol‐egg yolk‐polymyxin B agar medium and confirmed by morphological and biochemical tests. B. cereus was present in 28.5% of rice and rice products (100% of boiled rice), 40% of fish, 80% of chicken and meat products, 30% of spices and 87% of ice creams. Pasteurized milk and milk products and protein‐rich food powders containing milk or cocoa were also contaminated with B. cereus. The average count of B. cereus varied from 2 × 102 to 5 × 105/g. The response of cells and spores from 6 randomly selected isolates of B. cereus to antibiotics and to heat treatment was identical. However, both vegetative and spore forms of these isolates exhibited subtle differences in radiation resistance. Pathogenicity of all isolates was determined by their ability to lyse human erythrocytes. Five of the six isolates selected produced a strong nonhemolytic toxin which is lethal to mice.
The effectiveness of a radicidation process using 1 kGy of gamma radiation was evaluated with respect to the destruction of Vibrio parahaemolyticus contamination in shrimp. Dlo values of this pathogen ranged from 0.03 kGy in ji-ozen buffer to 0.10 kGy in naturally cantaminatedfrozen shrimp. The efJicacy of the process was demonstrated.
Lipopolysaccharide of Salmonella typhimurium was irradiated with gamma radiation at 10, 15, and 30 kGy doses. A dose of 30 kGy significantly detoxified the LPS (180 times). Mice were injected intraperitoneally with the radiodetoxified LPS, and it was found that it stimulated peritoneal macrophages as was evident from the enhancement of their acid hydrolases and cellular RNA content. Both LPS and radiodetoxified LPS exhibited antitumor activity against S180 cells in Swiss mice. Treatment with 20 jug/mouse of either LPS or 30 kGy LPS gave maximum survival of the mice (90%). These mice were found to resist the challenge of S180 cells (1 x 106).
The antitumor activity of lipopolysaccharide (LPS) and radio-detoxified LPS of Vibrio parahaemolyticus was tested against S180 cells in Swiss mice. The toxicity of the LPS was 200 times less than that of Salmonella typhimurium LPS. The V. parahaemolyticus LPS could be detoxified by exposure to gamma radiation. Both LPS and the irradiated LPS exhibited antitumor activity, though the irradiated LPS was less effective than the native LPS.These observations indicated that exposure to gamma radiation caused significant detoxification of V. parahaemolyticus LPS and the detoxified LPS still possessed considerable antitumor activity.
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