Potato Bacillus

(Bacillus mesentericus), a spore-bearing bacterium that looks like a thin rod (0.5–0.6 microns × 3–10 microns) and often forms long threads.

The vegetative cells of the potato bacillus are motile, gram positive, and form oval spores; the cells do not swell but maintain their cylindrical form. The colonies are yellowish brown, dry, and rugose. On the surface of liquid media the potato bacillus forms a thick, creased film; it forms a thin wrinkled coating on pieces of potato. It liquifies gelatin, forms alkalis and peptone in milk, and acidifies glucose, saccharose, and maltose. It does not decompose starch. The potato bacillus is widely distributed in nature (in soil, food products). It is a pathogen for animals and man. Its spores, entering dough with the flour or yeast, are not destroyed when the bread is baked. As they grow, the soft part of the bread becomes slimy and viscous, and the bread acquires an unpleasant odor.