EFFECT OF TEMPERATURE ON THE VEGETATIVE GROWTH OF TYPE AND FIELD STRAINS OF BACILLUS-CEREUS

Growth of eight selected potentially pathogenic strains of Bacillus cereus was evaluated in a rich medium at different temperatures. No strain grew at 50 degrees C; maximal growth-permissive temperatures were in the range 46-50 degrees C for six strains and under 46 degrees C for one strain. Faster growth occurred at 42 degrees C. Growth may be delayed at 20 degrees C, where the lag phase can reach 7 h. Furthermore at 20 degrees C, cells generally show an aggregation immediately in the early exponential stage, except for two strains. Owing to this aggregation, growth is more difficult to estimate by turbidimetry at lower temperatures. These data describe the behaviour of type and field strains between 50 degrees and 20 degrees C and can help the prediction of shelf-life of potentially contaminated products.