194 11 Bacillus cereus and Bacillus anthracis
major pathogenic species of Bacillus belong to p rotein or glycoproteins called S-layers, which
the “Bacillus cereus group” which consists of vary in molecular weights (40–200 kDa) among
seven species: B. cereus, B. anthracis, B. strains. Some bacilli express capsule consisting
thuringiensis, B. mycoides, B. pseudomycoides, of homo-polypeptide of D- or L-glutamic acid or
B. weihenstephanensis, and B. cytotoxicus. A heteropolysaccharides (carbohydrates). The cell
majority of these species produce enterotoxin wall of Bacillus species is composed of peptido-
and cause gastroenteritis. Some strains of other glycan containing meso-diaminopimelic acid (m-
Bacillus species, such as B. circulans, B. lentus, DAP), teichoic acid, or teichuronic acid (uronic
B. megaterium, B. oleronius, B. licheniformis, acid-based polymer). Bacillus carries plasmids
B. thuringiensis, B. pumilus, B. subtilis, B. which encode for toxins, bacteriocins, or capsule
sphaericus, B. carotarum, B. pasteurize, and biosynthesis, and/or antibiotic resistance.
Paenibacillus polymyxa, may produce Growth temperature varies between 4 °C and
enterotoxin. 50°C with an optimum temperature from 25 to
37°C. Psychrotolerant bacilli are found in milk
and dairy products. Some thermophilic strains
Biology can grow at 75°C. B. cereus usually does not
grow below pH 4.5. Biophysical and biochemical
Bacillus species are Gram-positive, aerobic, properties including motility, capsule production,
endospore-forming rods (Fig. 11.1) with an spore structure, hemolysis pattern, urea utiliza-
exception of B. saliphilus, which is an endospore- tion, nitrate reduction, and sensitivity to penicil-
forming coccus. The size of the vegetative cells is lin can be used to differentiate the major
in the range of 0.5 × 1.2–2.5 × 10 μm and occurs pathogenic Bacillus species (Table 11.1).
singly or in chains. Most bacilli are motile and Illustration of hemolytic and phospholipase
express peritrichous flagella. The colonies activity on blood agar and egg yolk agar plates is
formed by the bacilli are rough with irregularly shown in Fig. 11.3.
shaped perimeter and exhibit swarming patterns, Bacilli produce round, oval, ellipsoid, or
while B. polymyxa forms a round smooth circular cylindrical endospores located centrally to the
colony (Fig. 11.2). The members of the genus terminal end (Fig. 11.1). The spore contains
Bacillus carry a crystalline surface layer of a signature molecule, dipicolinic acid
Fig. 11.1 (a) Phase-contrast light microscopic picture of electron microscopic picture of a spore from Bacillus
cells of Bacillus cereus showing ellipsoid or cylindrical anthracis
spores (see arrows), (b) schematics of a transmission
