Analysis of broth-cultured Bacillus atrophaeus and Bacillus cereus spores

To compare physical properties of spores that were produced in broth sporulation media at greater than 10(8) spores ml(-1).

Bacillus atrophaeus reproducibly sporulated in nutrient broth (NB) and sporulation salts. Microscopy measurements showed that the spores were 0.68 +/- 0.11 microm wide and 1.21 +/- 0.18 microm long. Coulter Multisizer (CM3) measurements revealed the spore volumes and volume-equivalent spherical diameters, which were 0.48 +/- 0.38 microm(3) and 0.97 +/- 0.07 microm, respectively. Bacillus cereus reproducibly sporulated in NB, sporulation salts, 200 mmol l(-1) glutamate and antifoam. Spores were 0.95 +/- 0.11 microm wide and 1.31 +/- 0.17 microm long. Spore volumes were 0.78 +/- 0.61 microm(3) and volume-equivalent spherical diameters were 1.14 +/- 0.11 microm. Bacillus atrophaeus spores were hydrophilic and B. cereus spores were hydrophobic. However, spore hydrophobicity was significantly altered after treatment with pH-adjusted bleach.

The utility of a CM3 for both quantifying Bacillus spores and measuring spore sizes was demonstrated, although the volume between spore exosporium and spore coat was not measured. This study showed fundamental differences between spores from a Bacillus subtilis- and B. cereus-group species.

This is useful for developing standard methods for broth spore production and physical characterization of both living and decontaminated spores.