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• Bacillus


  Family: Bacillaceae, Genus: Bacillus
• Ahmad Al-Hayek
• Bacillus


  • Aerobic Spore Forming Bacillus spp
• Bacillus


  • Pathogenic: B. anthracis, B. cereus
  • Non-pathogenic: e.g. B. subtilis

  
• Dr: Abdelraouf Elmanama / islamic university
• B. cereus


  • They are aerobic (some are facultative anaerobe) grow best under aerobic condition
  • Large Gram positive or Gram variable rods with size range (0.5x1.2μm to 2.5x10 μm)
  • Endospore forming bacilli, spores located in the center of non motile cells and have square ends and arranged in long chain
  • Most of species are catalase positive, fermentative or respiratory or both. Some of them do not attack sugar
  • Motile with the exception of B. anthracis and B. mycoides
  • The bacilli are among the most common laboratory contaminants

  
• Bacillus anthracis


  • Colonies have a cut glass appearance in transmitted light
  • Hemolysis is uncommon

  
• The spores are resistant to environmental changes, withstand dry heat and certain disinfectant and persist for years in dry earth
• Important Bacillus species


  • Bacillus anthracis
  • B. alvei, B. brevis, B. cereus, B. coagulans, B. circulans, B. subtilis, B. licheniformis

  
• Most Bacillus spp.


  • Saprophytic, found on vegetation and in soil, water, air and dust
  • Among the most common laboratory contaminants
• Opportunistic pathogens


  Some Bacillus species like B. cereus, B. licheniformis can cause disease if conditions are right

  
• Obligate pathogen


  B. anthracis is considered an obligate pathogen of animals and humans
• B. anthracis


  • Highly pathogenic for man and animals, cause disease called anthrax, primarily of domestic animals
  • Human anthrax are rare but occasionally has been connected by farmers, Veterinarian, slaughterhouse workers, and workers at plant processing imported goat hair, wool, or hides (industrial anthrax)
  • Infrequent (rare) infections have been attributed to B. cereus, but animal disease caused by other species are rare

  
• B. anthracis is found worldwide and considered always as pathogen

  
• Mode of infection for B. anthracis

  • Acquired by ingestion, inhalation, wounds, scratches and through skin
  • Mechanical transmission by blood feeding insects has been reported

  
• Pathogenesis of B. anthracis

  • Animals died of toxemia; exotoxins was found in the plasma of dead animals
  • The anthrax toxin is a complex consisting of three protein components: edema factor (EF), protective antigen (PA), and lethal factor (LF)
  • Components I and II cause edema with low mortality but with component III there is maximum mortality
  • Only encapsulated, toxigenic strains are virulent
  • The capsule is a poly- γ- D-glutamic acid and its antiphagocytic

  
• Pathogenesis of B. anthracis

  1. The spores usually enter through the skin or mucous membranes and germinate at the site of entry

  2. In the septicemic form, the vegetative bacilli spread via the lymphatic to the blood stream. Deaths is attributed to respiratory failure and anoxia caused by the toxin, blood fail to clot and enlargement of the spleen (splenomegaly) is produced

  3. In localized form lymph nodes of head and neck are infected

  4. In terminal stage large numbers of bacilli are shed from natural orifices

  
• Pathogenicity of B. anthracis

  • The organism is obligate pathogen. Peracute, acute, subacute, chronic and cutaneous forms of the disease were observed
  • The acute form mostly seen in cattle, sheep, horses and mules
  • The cutaneous form occasionally seen in horses and cattle

  
• Pathogenicity in humans


  • The form of the disease depends on the route of entry e.g., pulmonary anthrax (Wool Sorter Disease), cutaneous anthrax (malignant carbuncle or pustule)

  
• Signs of anthrax in infected animals and humans

  
• Clinical manifestations of diseases caused by Bacillus anthracis and other Bacillus species

  
• Direct examination: Smear from tissues or blood are made and stained with Grams, Giemsa or Wrights stains
• Cutaneous anthrax (malignant carbuncle or pustule)

  • Pustule

  
• Figure 2. Signs of anthrax in infected animals (A–C) and humans (D–G), Bhutan, 2010.

  
• Signs of anthrax in infected animals

  • A) The carcass of an affected bull, showing bloating
  • B) Bleeding of unclotted blood from a cow's nostril
  • C) Rod-shaped Bacillus anthracis bacilli from 1 of the infected animals

  
• Signs of anthrax in humans

  • D) Cutaneous anthrax causing severe inflammation of the arm
  • E) Typical black eschars on the hand and wrist, neck (scar), and leg
  • Persons who had contact with B. anthracis –infected animals and carcasses

  
• Direct examination


  1. Smear from tissues or blood are made and stained with Grams, Giemsa or Wrights stains

  2. The microorganism measure 0.5x1.2μm to 2.5x10 μm in length, arranged singly or in short chains

  3. Large square-ended, Gram positive rods suggest anthrax

  4. Clostridia may be isolated from tissue and blood but it does not grow aerobically, have no capsule, and have round ends

  
• Bacillus anthracis


  • The capsule is demonstrated by Giemsa stain where it appear as reddish-mauve surrounded large square ended rods known as M'Fadyean's Reaction and the capsule is unique consist of poly D-glutamic acid
  • It does not form spores in the living animals. Spores are formed under conditions unfavorable for multiplication of vegetative form
  • Grows well on blood agar with no haemolysis in contrast to other saprophytic bacilli

  
• Isolation and cultivation


  1. The organism grows well on all laboratory media

  2. Guinea pigs and mice inoculated with blood or suspension begin to die within 24 hrs

  3. Surface colonies appear after 24 hrs incubation and are gray-white, rough and some called "medusa head" they have a curled edge

  
• Bacillus anthracis. (A) Gram stain. 1500X. The cells have characteristic squared ends. (B) Endospore stain

  
• Figure 14.1 Bacillus anthracis in a bovine blood smear collected from a peripheral blood vessel showing squareended, blue bacilli in short chains surrounded by a pink (M'Fadyean's Reaction) capsule. (Polychrome methylene blue stain, ×1000)

  
• Antigenic nature of Bacillus anthracis

  • All strains appear to be Antigenically identical
  • Antigens are: Polypeptide capsule (poly D-glutamic acid), Somatic antigen (polysaccharides) and the toxins

  
• Resistance of Bacillus anthracis

  • Spores are more resistant to physical and chemical influences than are the vegetative form
  • Spores may survive for 22 years in dried cultures, remain viable in soil for years and did not affect by freezing
  • Destroyed by boiling for 10 minutes and by exposure to dry heat at 140 C for 3 hours
  • Disinfectants must be used in high concentration over long period of time, spores destroyed by 10-20% formalin in 10 minutes and by autoclaving at 121 C for 15 minutes
  • Wool, hides and horsehair should be sterilized by gas sterilization

  
• Immunity: By annual vaccination of animals in epidemic areas
• Bacillus cereus


  • Has been incriminated as the cause of gangrenous bovine mastitis and abortion in cows and ewes
  • In human it has been implicated in food poisoning
  • Spores germinates in different food where enterotoxins or emetic toxin may be produced
  • Two syndrome, the emetic and the diarrheal forms could be seen

  
• Figure 14.4 Bacillus cereus on sheep blood agar. The morphology resembles that of B. anthracis, but the colonies are usually strongly haemolytic

  
• Figure 14.3 Bacillus anthracis on sheep blood agar illustrating non-haemolytic, flat, 'ground-glass', dry colonies with irregular edges.

  
• Bacillus subtilis


  • Claimed to cause conjunctivitis, septicemia, endocarditis, respiratory infections and food poising in humans

  
• Bacillus licheniformis


  • Cause bovine, ovine and porcine abortions, occasionally may cause septicemia, peritonitis and food poisoning in humans

  
• Geobacillus stearothermophilus (previously B. stearothermophilus)

  • Spores are used to test the efficacy of autoclaving and other sterilizing procedures