|Bacteria that are rod shaped are classified as bacillus
(singular) or bacilli (plural). Escherichia and Bacillus , two common
genera that are bacilli, are shown here at 1000 X magnification. Escherichia are small rods that
occur in the intestinal tract of man and animals. Bacillus
are much larger rods that are common in the soil. Bacillus
tends to occur in chains and may produce spores which appear as oval regions that have not taken up the dye. Note that bacillus
with a lowercase "b" refers to any rod-shaped bacterium. Bacillus
with an uppercase "B" and underlined or italicized letters indicates a unique genus of
bacteria that are rod-shaped but must have other specific
characteristics to be in this genus (aerobic, spore-formers etc.)
Staining does not enable one to differentiate the various species of Bacillus.
Biochemical tests are conducted for this purpose.