Influence of agar content on the growth parameters of Bacillus cereus

Factors governing Bacillus cereus colony growth on agar media as modified b y the agar content (1-7%, w/v) were studied. Agar had a significant effect on the radial growth rate which diminished as the agar content increased. C ell density in colonies (colony density) was found to decrease during the i ncubation time, with lower values occurring in the presence of 1% agar. Siz e and DNA content of the cells grown on 1 and 7% agar were similar. An incr easing proportion of cell population growing on 7% agar produced spores dur ing the 24-h incubation period. It was shown that 'water condition' on the agar surface could be associated with colony density, with 7% agar media pr esenting the thinnest nominal thickness of the liquid film. On the other ha nd, the partial drying phenomena of the agar media which occur during prepa ration and incubation, could not account for the observed differences in co lony growth. (C) 2001 Elsevier Science B.V. All rights reserved.