Aerobic Spore-Forming Gram-Positive Rods Clinical Microbiology Review 170
ORGANISM PATHOGENICITY GRAM STAIN CULTURE KEY CHARACTERISTICS OTHER
Bacillusspp
Bacillus anthracis
Bacillus cereus
Must rule out
B. anthracis.
Potential bioter-
rorism organism.
Handle in BSC.
Submit to public
health lab for
confirmation.
2nd most impor-
tant pathogen in
genus.
Large spreading beta-
hemolytic colonies
with irregular edges
(Medusa head).
Whitish gray. May
be pigmented.
Large, adherent,
nonhemolytic, flat
to slightly convex,
irregular border,
ground-glass appear-
ance, comma-shaped
projections. Stands
up like beaten egg
white when touched
with loop.
Same as B. anthracis
except hemolytic.
Usually contaminants.
One of most highly
pathogenic microor-
ganisms. Causes
anthrax. Contracted
from contaminated
hides, wool, meat.
Rare in U.S.
Often environmental
contaminant. Can
cause local & systemic
infections, food
poisoning.
See B. anthracis
below.
Large with square
ends. May be in
chains. Oval, cen-
tral to subterminal
spores that aren’t
swollen. Looks like
bamboo. Spores
may not be seen in
direct smear.
Same as
B. anthracis.
Catalase pos.
Most are motile.
Nonhemolytic. (Beta
hemolysis rules out.)
Catalase pos.
Nonmotile.
Capsules seen in CSF &
blood smears.
Hemolytic. Motile.
