Aim: To investigate the effect of different growth conditions on Bacillus cereus
cell and spore properties.
Methods and Results: Bacillus cereus was grown on agar plates with different
surface water conditions (wet and dry) or viscosity. Cell populations displayed
different types of behaviour, and heterogeneity was manifested in cell motility
and dimension. Spore populations were heterogeneous regarding their properties,
namely size and thermal resistance. The smallest spores were produced
from flagellated cells, which also displayed jet-motility, growing on the wettest
agar. Cytometric analysis also revealed within the smallest spores a sub-population
labelled by propidium iodide (PI), indicating that spore populations were
partly damaged. Nonmotile cells grown on diffusion-limiting media were elongated
and produced the least thermal-resistant spores.
Conclusions: The micro-structural properties of the media were found to
influence cell and spore properties. Abundant surface water enabled flagellar
motility and resulted in a heterogeneous cell and spore population, the latter
including small and damaged spores. High viscosity gave rise to filamentous
cells and more heat-sensitive spores.
Significance and Impact of the Study: This study provides useful information
on conditions resulting in heterogeneous populations of damaged and heatsensitive
spores.
