Bacillus

B. anthracis

characteristics

• non-motile
• “bamboo rod” appearance 
• Produces endospores
• Appearance in 5% SBA: 
  
  • Medusa head 
  • Ground glass appearance 
  • Beaten egg whites
• In MHA: 
  
  • String of Pearls

Virulence factors

• Protective Antigen – facilitates transport of two other protein into the cell. 
• Edema factor (adenylate cyclase) – responsible for edema 
• Lethal factor (protease) – primarily responsible for death. 
• D-glutamic acid capsule – resistant to hydrolysis

Disease association

• Cutaneous anthrax – most common Eschar (malignant pustule) – black necrotic lesion. 
• Gastrointestinal Anthrax – most severe 
• Pulmonary Anthrax (Woolsorter’s / Ragpicker’s Disease) 
• Injectional Anthrax – associated with “skin popping”

B. cereus

Characteristics

• Penicillin resistant 
• Betahemolytic 
• MOTILE 
• Frosted glass appearing colony 
• Feathery, spreading, beta hemolytic colonies

Virulence factors

• Diarrheal – responsible for most symptoms. 
  
  • Hemolysin BL 
  • Nonhemolytic enterotoxin 
  • Cytotoxin K
• Emetic 
  
  • Cereulide – heat-stable, proteolysis, acid-resistant

Disease association

• Opportunistic
• Associated with food borne disease
• Causes PROGRESSIVE ENDOPHTHALMITIS
• Some strains can carry B. anthracis toxin genes.

B. thuringensis

Characteristics

• Produces parasporal crystals

Virulence factors

• Harbors genes of B. cereus associated enterotoxins