Bacillus - Microbiology - Lecture Slides, Slides of Microbiology

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Bacillus

 ~ 60 species; Gram-positive or Gram-variable bacilli

• Large (0.5 x 1.2 to 2.5 x 10 um)
• Most are saprophytic contaminants or normal flora
• Bacillus anthracis is most important member

 Produce endospores

 Aerobic or facultatively anaerobic

 Catalase positive (most)

• Rapidly differentiates from Clostridium

 Bacillus spp. are ubiquitous

• Soil, water, and airborne dust
• Thermophilic (< 75°C) and psychrophilic (>5-8°C)
• Can flourish at extremes of acidity & alkalinity (pH 2 to 10)

General Characteristics of Bacillus

Bacillus anthracis

Summary of

B. anthracis Infections

Epidemiology of Bacillus anthracis

 Rare in the US (1974-1990, 17 cases reported by CDC)

 Enzootic in certain foreign countries (e.g., Turkey, Iran,

Pakistan,and Sudan)

 Anthrax spores infectious for decades

• Biologic warfare experiments (annual tests for 20 years)  Gruinard, off western coast of Scotland  4 x 10e14 fully virulent spores exploded  Eliminated in 1987 (formaldehyde & seawater)

 Three well-defined cycles

• Survival of spores in the soil
• Animal infection
• Infection in humans

Epidemiology of Bacillus anthracis (cont.)

 Primarily a disease of herbivorous animals

 Most commonly transmitted to humans by direct

contact with animal products (e.g., wool and hair)

 Also acquired via inhalation & ingestion

• Increased mortality with these portals of entry

 Still poses a threat

• Importing materials contaminated with spores from these countries (e.g., bones, hides, and other materials)
• Usually encountered as an occupational disease
• Veterinarians, agricultural workers

Clinical Presentation of Anthrax

Inhalation Anthrax

 Virtually 100% fatal (pneumonic)

 Meningitis may complicate cutaneous and

inhalation forms of disease

 Pharyngeal anthrax

• Fever
• Pharyngitis
• Nneck swelling

Clinical Presentation of Anthrax

Gastrointestinal (Ingestion) Anthrax

 Virtually 100% fatal

 Abdominal pain

 Hemorrhagic ascites

 Paracentesis fluid may reveal gram-positive rods

Characteristic Bacillus anthracis Other Bacillus spp. Hemolysis Neg Pos Motility Neg Pos (usually) Gelatin hydrolysis Neg Pos Salicin fermentation Neg Pos Growth on PEA blood agar Neg Pos

Key Characteristics to Distinguish between

B. anthracis & Other Species of Bacillus

 Bacillus thurigensis

• BT corn; Other GMO’s (genetically modified organisms)

 Bacillus stearothermophilus

• Spores used to test efficiency of killing in autoclaves

Other Bacillus spp.