Bacillus anthracis

Question 1

Disease

Answer 1

• anthrax ->common in animals; rare in humans.
• Human 3 forms: cutaneous, pulmonary (inhalation), & gastrointestinal.
• spread by spores

Question 2

Important Properties

Answer 2

• large gram-positive rod with square ends, in chains
• antiphagocytic capsule is made of D-glutamate
• nonmotile
• Anthrax toxin is encoded on one plasmid, & polyglutamate capsule is encoded on different
  plasmid.

Question 3

Transmission

Answer 3

• Spores persist in soil for years.
• Humans mostly infected cutaneously -> trauma to
  skin allows spores on animal products (hides, bristles, wool) to enter.
• Gastrointestinal anthrax -> contaminated meat ingested.
• Spores inhaled into respiratory tract-> Pulmonary (inhalation)
  anthrax
• Inhalation anthrax not communicable (P to P).
• After inhaled into lung, organism moves rapidly to
  mediastinal lymph nodes-> hemorrhagic mediastinitis. - leaves lung rapidly, not
  transmitted by respiratory route to others.

Question 4

Pathogenesis

Answer 4

• production of 2 exotoxins, collectively anthrax toxin= edema factor & lethal factor.
• each have 2 proteins in an A–B subunit configuration.
• A (active) subunit-> enzymatic activity
• B (binding) subunit -> protective antigen.

Protective antigen (antibody against this protein protects against disease) forms pores in human cell membrane allows edema factor & lethal factor to enter cell.

Question 5

Pathogenesis: Edema factor

Answer 5

• exotoxin
• adenylate cyclase -> increase in intracellular concentration of
  cyclic AMP->
  outpouring fluid from cell into extracellular
  space-> edema.
• similar action to cholera toxin.

Question 6

Pathogenesis: Lethal factor

Answer 6

• protease cleaves phosphokinase-> activates mitogen-activated protein kinase (MAPK) signal transduction pathway-> controls human cells growth & cleavage of phosphokinase inhibits cell growth.

Question 7

Clinical Findings

Answer 7

• cutaneous anthrax lesion-> painless ulcer with black eschar (crust, scab).
• Local edema-> malignant pustule.
• Untreated cases -> bacteremia & death.

Pulmonary (inhalation) anthrax (wool-sorter’s disease) -> symptoms resembling influenza (dry cough & substernal pressure)-> hemorrhagic mediastinitis, bloody pleural effusions, septic shock, & death.

• pneumonia not present but Mediastinal widening X-ray.
• Hemorrhagic mediastinitis & meningitis severe life-threatening complications.

Gastrointestinal anthrax symptoms-> vomiting, abdominal pain, & bloody diarrhea.

Question 8

Laboratory Diagnosis

Answer 8

Smears-> large, gram-positive rods in chains.
Spores not seen-> form in insufficient nutrients but nutrients plentiful in infected tissue.

Nonhemolytic colonies form on blood agar aerobically.

Bioterror attack: rapid diagnosis using polymerase chain reaction (PCR)–based assays or
direct fluorescent antibody test (detects antigens of organism in lesion).

Serologic tests (enzyme-linked immunosorbent assay (ELISA) test) for
antibodies, require acute & convalescent serum samples & used to make diagnosis retrospectively.

Question 9

Treatment

Answer 9

• Ciprofloxacin or Doxycycline
• No resistant strains

Question 10

Prevention

Answer 10

• Ciprofloxacin or doxycycline -> prophylaxis
• High risk immunized with cellfree vaccine containing purified protective antigen as immunogen.
• Vaccine-> weakly immunogenic & 6 doses of vaccine over 18-month period given.
• Annual boosters given.
• Incinerating animals that die of anthrax, rather than
  burying them-> prevent soil spore contamination.