Salmonella~train S30 (hyperphospholipase A producing) was subjected to physical (ultraviolet light, UV) and chemical mutagenic (N-methyl-N-nitro-N-nitrosoguanidine, NTG) treatments to obtain phospholipase A deficient (negative) mutants. The mutants were identified by their inability to form a zone of clearance around the colony. The mutants showing no zone of clearance on egg yolk agar were further tested for their specific phospholipase A activity. All the mutants showed no zone of clearance on egg yolk agar. Most of the mutants retained intracellular phospholipase A activity, whereas extracellular phospholipase A activity was retained only in a few mutants. The mutant showing no zone of clearance on egg yolk agar and without any specific extracellular/intracellular phospholipase A activity was selected (Snt~) to compare the pathogenicity of the parent (S30> and mutant strains in the rabbits. Histopathological examination of different organs, viz. intestine, lungs, liver and kidney, revealed marked changes in these organs with parent strain and only mild changes with the mutant strain. These histopathological findings showed that phospholipase A of Salmonella could be correlated with the pathogenicity of the organism.
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