bacillus anthracis spring 2011
Post on 24-May-2015
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Morphology and Physiology
• 1) Gram positive, encapsulated bacilli• (single or paired)• 2) Large (1-8μm to 1-1.5μm); sporeforming,• nonmotile, facultative anaerobe bacilli.• 3) Spore size: 1-2 μm; central or terminal.• Germinate readly in an environment at • 37° C, rich in amino acids, nucleosids, • and glucose
• 4) Endospores can survive for decades.• 5) Capsule: poly-D-glutamic acid.
Immunogenic.• 6) Colonies: Nonhemolytic “curled-hair”
white to gray.
• B.- Taxonomy:
Genus: Bacillus (Group B. cereus)
Species: B. anthracis, B. cereus,
B. mycoides, B. thuringiensis
C.- Virulence Factors:• 1.- Capsule: Antiphagocytic• 2.- Exotoxins: Three components combine
to form two binary toxins.• a) Edema toxin: Protective antigen (bin_
ding to host cell) and edema factor
(calmodulin-dependent adenylate cy-
clase).
Massive edema, inhibit Neutrophils
function.
• b) Lethal toxin: Protective antigen and
lethal factor (Zinc metalloprotease)
Stimulates macrophages to release
TNF-α and IL-1 β
• D.- Epidemiology:
1) B. Anthracis primarily infects
herbivorous.
2) Humans are infected through exposure to spores from animal hair and wool.
• 3) Reservoir: Animals, carcases, soil.• 4) Routes:• a.- Inoculation of spores through skin:• 95% of cases.• b.- Ingestion: Common in hervivorous• very rare in humans.• c.- Inhalation (Wool-sorters’ disease).• LD50: 2,500 to 55,000 spores.
E.- Clinical Manifestations:1.- Pathogenesis:
*Endospores are phagocytosed by macropha_
ges and carried to regional lymph nodes.
*Endospores germinate inside the macropha_
ges and vegetative bacteria are then released.
*Bacillus multiply in the lymphatic system
and cause bacteremia then massive septcemia
2.- Cutaneous anthrax:
*Occupational exposure to spores that are intro_
duced subcutaneously through a cut or abrasion
•
• *After 3 to 5 days: Painless, pruritic macule or papule, then a vesicle undergoes to
central necrosis and drying leaving a black eschar, surrounded by edema and purplish vesicles.
• 3.- Gastrointestinal and Oropharyngeal Anthrax:
*Two to five days after the ingestion of endospore-contaminated meat.
• *Bacilli is seen in mucosal and submucosal lymphatic tissue (mesenteric lymphadenitis).
• *Massive edema and mucosal necrosis in the terminal ileum or
cecum.
•
• *Nausea, vomiting, and malaise, progressing to • bloody diarrhea, acute abdomen or sepsis. As_• citis, blood loss, fluid and electrolytes imbalan_• ces, shock.• *Death results from intestinal perforation or • anthrax toxemia.
• 4.- Inhalation Anthrax:• *Two to 43 days after exposure to spores.• *Endospores are engulfed by alveolar
• macrophages and transported to the mediastinal
and peribronchial lymph nodes, after multiply,
causes hemorrhagic mediastinitis and then
bacteremia.• *Two days to six weeks after exposure: Fever,
nonproductive cough, myalgia, and malaise.
Chest X-rays show a widened mediastinum and
marked pleural effusions.
After one to three days: dyspnea, strident cough,
chills, and death.
Focal, hemorrhagic necrotizing pneumonitis,
• with similar lesions in peribronchial lymph
nodes.• 5.- Anthrax meningitis:
*Bacillus can spread to CNS by hematogenous or
lymphatic routes in all types of anthrax.
*Fatal: 1 to 6 days after the onset of illness.
*Meningeal symptoms and nuchal rigidity plus
fever, fatigue, myalgia, headache, nausea, vo_
miting, and sometimes agitation, seizures and
delirium. Followed by rapid neurologic degene_
ration and death.
•
• *Hemorrhagic meningitis, with extensive edema, inflammatory infiltrates, and numerous bacilli in the leptomeninges.
• CSF is often bloody with many bacilli.
• F.- Laboratory diagnosis:• 1) Exudates, blood, CSF, aspirates
fluids, tissues.• *Direct microscopy exam: Gram
stain• *Culture: Blood agar,nonhemolytic
colonies grow rapidly and are firmly adherent to the agar.
“Medusa heads”, serpentine chains of bacilli.
• *PCR
• 2) Serologic and Immunologic test:
• *ELISA: Antibodies anti-capsule or exotoxins.
• G.- Treatment and Prophylaxis:
1) Ciprofloxacin or Levofloxacin
2) Doxycycline, or Erythromycin, or Chloramphenicol.
Amoxicillin in pregnant women.
• 3) Corticosteroid therapy for severe edema
• 4) Antitoxin therapy
• *** Vaccine.
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