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Bacillus
Bacillus
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Classification
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All are large Gram-positive bacilli
Are aerobic
Form endospores
Most are found in dust and soil
Bacillus anthracis is the major pathogen in the
group
Morphology and Cultural Characteristics
(Bacillus anthracis)
Bacillus anthracis
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G+B with square cut ends
Form endospores
Non-motile
Capsule made of glutamic acid (a polypeptide).
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The capsule is not found in cultured bacteria unless
the bacteria are grown on bicarbonate containing media
and in the presence of increased CO² concentrations.
Gram stain of Bacillus sp.
Endospores of Bacillus sp.
Bacillus anthracis
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Grow well on ordinary lab media producing large
granular colonies with a coarse texture.
B. anthracis
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Virulence factors
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Capsule helps organism to resist phagocytosis but
antibodies are not protective.
Exotoxin is very complex and is produced only
when the bacteria is growing in animal tissues.
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Toxin production is mediated by a temperature sensitive
plasmid.
The toxin consists of three protein components (maximum
toxicity occurs when all three components are present).
Bacillus anthracis
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Protective antigen (PA) reacts with host cell tissue
receptors where it is proteolytically activated so that it
binds LF and EF to allow entry of LF and EF into the host
cells via endocytosis.
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Injection of PA will result in the production of antibody
against PA that provides short term immunity.
Lethal factor (LF) Both PA and LF are required for lethal
activity.
Edema factor (EF) Both PA and EF are required for
edema to occur.
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EF has adenylate cyclase activity and it becomes active
when it enters eucaryotic cells.
This results in an increase of cAMP and resulting edema.
Bacillus anthracis
Bacillus anthracis
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Clinical significance
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Anthrax which is the disease caused by B.
anthracis is essentially a disease of animals who
acquire the organism by ingestion or inhalation of
spores.
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The spores are extremely resistant to adverse
chemicals and physical environments.
They may remain a source of infection in soil for 20-30
years.
Man acquires anthrax usually from contact with
animal products; less commonly from working in
an agricultural setting with infected animals.
Bacillus anthracis
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Man may acquire the organism through skin
abrasions, by inhalation of spores, or by
ingestion. The disease that develops depends
upon the mode of transmission:
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Pulmonary (Woolsorter‘s disease) Spores are inhaled
and germinate in the lungs where they multiply and
spread to cause a fatal septicemia or meningitis.
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This is the most serious form of the disease.
Intestinal anthrax results from ingestion of spores.
Pulmonary anthrax
Bacillus anthracis
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Cutaneous anthrax when organism comes in through
skin abrasions;
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Most common form;
most damage comes from the invasion but the toxin may play a
role;
Spores enter through a cut, germinate, and vegetative cells
multiply;
There is an acute host inflammatory response, but the capsule
probably prevents phagocytosis;
Exotoxin release and invasive damage result in rapid
development of a malignant pustule;
Occasionally, without treatment, the organism will disseminate to
cause septicemia and death in a few days (rare because of B-lysin
activity in the bloodstream that kills the bacteria);
Vascular injury with edema, hemorrhage, and thrombosis may
occur;
Death results from respiratory failure and anoxia caused by
actions of the toxin on the central nervous system (toxemic
degeneration).
Cutaneous Anthrax
Bacillus
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Antibiotic susceptibility and treatment
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Penicillin or tetracycline
A short-term PA vaccine is available for industrial
workers and others at high risk.
Other Bacillus species
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Bacillus subtilis, and occasional other species
may occasionally cause opportunistic infections.
Bacillus cereus is a major cause of enterotoxin
food poisoning;
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The toxin is protein in nature and can be destroyed by
heating;
Food poisoning occurs after ingestion of pre-formed toxin;
 Vomiting occurs 1-5 hours after ingestion
Bacillus
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B. cereus is also an opportunistic pathogen that
has been cultured from cases of septicemia,
endocarditis, meningitis, wound infections,
pneumonia, and fulminant eye infections
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In addition to the enterotoxin that bacteria may
produce, a dermonecrotic and a lethal toxin,
hemolysins, lecithinase, proteases, and nucleases may
be involved in its pathogenesis
Clindamycin with or without gentamycin may be used for
treatment of infections