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 septcemia2.- 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.