Download B. anthracis

Bacillus
B. anthracis: anthrax of the animals and humans.
B. cereus: food poisoning; opportunistic infections.
Morphology and Physiology
Aerobic or facultatively anaerobic.
Large gram-positive rods, have
square ends, arranged in long
chains.
Spore is located in the center of
the cell.
Most are saprophytic (soil, water,
air, and on vegetation.)
B. anthracis
Physiology and Structure
B. anthracis is encapsulated and non-motile.
The capsule consists of polypeptide (poly-D-glutamic
acid).
The spores can withstand dry heat and certain
disinfectants for moderate periods, and persist for
years in dry earth. Animal products contaminated with
anthrax spores can be sterilized only by autoclaving.
B. anthracis
Pathogenesis and Immunity
Primarily a disease of herbivores (sheep, cattle, horses); humans
are rarely affected.
Being used by the terrorists as a biological warfare.
In animals, portal of entry is mouth and GI tract. In humans,
scratches in the skin (95% of infection), ingestion or inhalation lead
to infection.
Inhalation is the most likely route for infection with biological
weapons (LD50: 2,500-55,000).
The spores germinate in the tissue at the site of entry, and growth
of the vegetative forms results in gelatinous edema and congestion.
Bacillus spread via lymphatics to the blood and other tissues.
Spores in the soil
Spores from
Germination of
the carcasses
spores in the soil
Grazing animals infected through
injured mucous membrane
Infection in humans
B. anthracis
Pathogenesis and Immunity
Virulence factors
Capsule (encoded from a plasmid)
Exotoxins (A-B toxins encoded from another plasmid)
Edema toxin is composed of protective antigen (Bsubunit) and edema factor (has adenylate cyclase
activity). This toxin complex increases vascular
permeability which leads to shock.
Lethal toxin is composed of protective antigen and
lethal factor (a metalloprotease). This toxin stimulates
macrophages to release proinflammatory cytokines.
B. anthracis
Clinical Diseases
Cutaneous anthrax (malignant pustule): develops in 12-36
hours. The papule rapidly changes into a vesicle, then a
pustule, and finally a necrotic eschar. The infection may
disseminate, giving rise to septicemia.
Inhalation anthrax (wool-sorters’ disease): long incubation
time (2 months or more). Mediastinitis (enlargement of
mediastinal lymph nodes), sepsis, and meningitis (50%
patients). Pulmonary disease rarely develops.
Gastrointestinal anthrax (very rare): symptoms vary
depending on the sites of infection. Can result in ulcers in
the mouth and esophagus, or abdominal pain, vomiting and
bloody diarrhea. May develop into septicemia rapidly with a
mortality that can be 100%.
B. anthracis
Laboratory Diagnosis
Specimens: fluid or pus from local lesion, blood, or sputum.
Smears: serpentine chains (a characteristic of B. anthracis) of
large gram-positive rods without spores. Immunofluorescence
stain for dried smears.
Culture: produces nonhemolytic gray colonies with sticky
consistency on blood agar plates.
Identification: non-motility; gelatin stab: inverted fir tree; or
selected biochemical tests.
Serological tests: detection of antibodies to lethal toxin and
edema toxin.
B. anthracis
Treatment
Penicillin is the drug of choice. Resistant to sulfonamides
and cephalosporins.
Control
Proper disposal of animal carcasses (burning or deep burial
in lime pit).
Autoclaving of animal products.
Protective clothing and gloves for handling infected animals.
Vaccination of domestic animals.
Immunization of persons at high risk with a cell-free vaccine.
B. cereus and other bacillus species
Ubiquitous organisms; primarily opportunistic pathogens.
B. cereus: the most important among them.
Noncapsulated and motile, causing
gastroenteritis: emetic form and diarrheal form.
ocular infections: acute panophthalmitis occurs after
traumatic, penetrating injuries of the eye with a soilcontaminated object.
intravenous catheter-related sepsis.
Other infections: endocarditis, pneumonitis, sepsis,
meningitis, etc.
Symptomatic treatment is adequate for B. cereus gastroenteritis.
The treatment of other Bacillus is complicated because the course
is rapid and progressive and they are resistant to multiple drugs.
Food poisoning can be prevented by quick consumption and proper
storage of food.
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B. cereus food poisoning
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