This document discusses the genus Bacillus, including Bacillus anthracis and Bacillus cereus. It covers their general characteristics, cultural characteristics, pathogenesis and virulence factors. B. anthracis causes anthrax and contains two plasmids and toxins that play a role in its virulence. B. cereus causes two types of food poisoning and contains enterotoxins and emetic toxins. The transmission of B. anthracis is usually through cuts or ingestion while B. cereus is usually transmitted through contaminated food. Diagnosis involves culturing and tests, and prevention involves proper food handling and hygiene.
3. GENERAL CHARACTERISTICS
oGram Positive bacteria.
oAerobic or facultative anaerobes.
oFormed unique type of resting cells called Endospore.
oBacillus anthracis spores are geographically ubiquitous in soils.
o Non motile.
oMostly Catalase Positive.
oSource of antibiotics.
oVersatile in degrading the complex macromolecules.
oGenus include psychrophilic, mesophilic and thermophilic spieces.
o2 spieces are important Medically :
o 1) Bacillus anthracis 2) Bacillus cereus
4. CULTURAL CHARACTERISTICS:
oTemperature range for growth is 12˚C-45˚C (optimum is 35˚C-37˚C)
oOn Agar plate:
Irregular colonies formed with raised dull, opaque, greyish white with a
frosted glass appearance, 2-3mm in diameter
oOn Blood agar:
The colonies are nonhemolytic.
oIn Broth growth occurs as floccular deposits.
oWhen Bacillus anthracis is grown on the surface of a solid medium
containing 0.05-0.50 units of penicillin/ml, in 3-6 hrs. the cells become large,
spherical and occur in chain on the surface of the agar resembling a string of
pearls.
oOn ordinary nutrient agar Bacillus subtilis shows rough circular colony,
fuzzy white or slightly yellow with jagged edges.
oBacillus anthracis shows no growth on MacConkey agar.
oMany are Beta Haemolytic.
7. PATHOGENESIS & VIRULENCE:
B. anthracis considered major animal pathogen causing anthrax in herbivores & other
mammals.
TYPES OF ANTIGENS PRESENT:
•Somatic or O antigen.(cross reactive).
•Capsular or K antigen.
•Flagellar or H antigen.
•Spore Antigen.
B. licheniformis produces extracellular substances.
Virulence Factors:
B. anthracis contain 2 toxic plasmids:
8. PATHOGENESIS & VIRULENCE
(CONT.)
Combination of lethal toxin, which constitutes the protective antigen and lethal factor
Edema toxin which constitutes the PA and EF can induce severe cases of disease
From these factor PA plays crucial role in toxic action
2. pX02 which encodes the production of capsule.
1. pX01, which secrete three proteins:-
Protective antigen(PA) cause food poisoning.
Lethal factor(LF) cause imbalance of water homeostasis.
Edema factor(EF).
9. VIRULENCE FACTORS:
B. cereus:
Recent studies on the ocular virulence factors of B. cereus demonstrated that hemolysin BL,
a tripartite dermonecrotic permeability factor and crude exotoxin preparations in vivo caused
endophthalmitis, clinically characteristic of the organism within 4 hours of inoculation.
It produces heat stable emotic toxin ; enterotoxin causes fluid accumulation in ileac lobe &
severe mucosal damage.
1. The enterotoxin causing diarrhea .
2. The emetic toxin causing vomiting and nausea .
Cereulysin instantly lethal when given to rabbit , causes bovine abortion.
May have three different forms of enzyme activity related to lecithinase like
activity;
phosphatidylcholine hydrolase is the most studied form and frequently referred
to as phospholipase C.
This enzyme may have a secondary role in ocular infections by disrupting host
cell membrane phospholipids exposed by the action of other toxins.
10. TRANSMISSION OF ANTHRAX (BY
B. ANTHRAX):
Common ways of transmission of the anthrax disease are through:
Wounds.
The pharynx.
Gastrointestinal tract.
The digestive system after ingesting spore contaminated food or water.
Skin lesions or abrasions caused by biting flies.
The breathing in of air containing anthrax spores.
Mode of transmission(B. cereus ):
The primary mode of transmission is via :
The ingestion of B. cereus contaminated food (emetic type of food poisoning has been
largely associated with the consumption of rice and pasta)
While the diarrheal type is transmitted mostly by milk products, vegetables and meat.
11. DIAGNOSIS:
B. anthracis:
The bacteria may be found in cultures or smears in cutaneous (skin) anthrax and in
throat swabs and sputum in pulmonary anthrax.
Chest X-rays may also show characteristic changes in and between the lungs.
Once the anthrax is disseminated, bacteria can be seen in the blood using a
microscope.
B. cereus:
Doctors diagnose B. cereus food poisoning by testing the patient's
feces for the bacteria then matching the strains of bacteria within the
samples to either a known contaminated food source or strains known
cause illness.
12. BIOCHEMICAL TEST OF BACILLUS
ANTHRACIS:
Biochemical characteristics B. anthracis
Gram Staining Gram Positive (+ve)
Indole Positive (+ve)
Motility Non motile
Capsule Capsulated with a poly-γ-glutamic acid capsule.
Shape Rods
Spore Endospore formation
Urease Negative (-ve)
14. Colonies of different bacillus species on agar
plate.
Bacillus anthracis colonies growth on
nutrient and blood agar.
15. PREVENTION FOR B.
CEREUS:
Ensure food is maintained either at a temperature above 60°C or
refrigerated below 4°C.
Cool cooked foods that will not be immediately consumed to below 4°C
within 6 hours.
When reheating food, ensure that the temperature reaches at least 74°C.
PREVENTION FOR B. ANTHRACIS:
Cases of human-to-human contagion have not been reported in the case of anthrax
which suggests that the primary form of infection is the spore.
The disease can be avoided by maintaining proper hygiene and protection during the
handling of infected animals.
Instruments and materials contaminated used on patients with anthrax should be
autoclaved or incinerated as the usual practice.
