Bacillus spp

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Bacillus spp

• Strictly aerobic, facultatively anaerobic
• Spore-forming, medium-to-large rods
• Most motile, many Gram variable
• Major pathogen is B. anthracis

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Anthrax in Ancient History

• Egyptian and Mesopotamian writings from 5000 BC
  
• Two of the plagues from Exodus 9 (...murrain of
  beasts.... and ...plague of boils and
  blains....)
• Virgils treatise on agriculture

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Cutaneous Anthrax

• Spores deposited in abrasion, insect bite
• Germinate, vegetative cells multiply and produce
  toxin
• Vesicle appears, contains serous fluid which
  later becomes hemorrhagic and blue-black
• Ruptures, leaving round sharp-edged ulcer with
  hemorrhagic necrotic tissue

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Cutaneous Anthrax

• Ulcer dries, edges separate from surrounding
  skin, sloughs off
• Lesion develops fully, results in ulceration,
  even with appropriate therapy, started early
• 5-20 of untreated patients develop septicemia
  and generalized infection

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Inhalation AnthraxWoolsorters Disease
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Inhalation AnthraxWoolsorters Disease

• After inhalation, spores may be dormant for
  months
• delayed germination can result in prolonged
  incubation periods
• monkeys exposed to four spore LD50s
• 15 - 20 survived in lung tissue gt 42 days
• 2 remained gt 50 days
• lt 1 (still a substantial number) recovered gt 75
  days
• prolonged incubation period in Sverdlovsk
  outbreak gt lethal numbers of spores persisted gt
  6 weeks post exposure

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Gastrointestinal Anthrax
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AnthraxDomestic, wild animals occurs in most
US states

• Ruminants (particularly cattle)
• peracute disease course may be 1 - 2 h
• rapidly-developing cerebral anoxia, pulmonary
  edema
• death often reported as due to lightning strike
• acute disease course 24 - 48 h
• abrupt onset of fever, anorexia, excitement,
  pharyngeal, lingual edema
• followed by depression, convulsions main feature
  at death edema

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Anthrax

• Horses course acute-to-subacute (survive 96 h)
• septicemia, enteritis, colic
• transmission via insect bite similar to human
  cutaneous anthrax
• local subcutaneous edema affects throat, ventral
  thorax, abdomen
• Hair from horses dead of anthrax used as binder
  in plaster
• Spores left in plaster in 19th century detected
  in 20th century

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Anthrax

• Omnivores, carnivores
• natural resistance, more likely to recover
• subacute-to-chronic
• usually after ingestion of contaminated meat
• lingual, pharyngeal edema dyspnea, dysphagia
• death due to asphyxia
• Disease in wild carnivores
• mainly due to consumption of meat from
  anthrax-affected animals shot as food for
  carnivores in game farms

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PathogenesisBasic principles apply across species

• Pigs
• form of cutaneous anthrax (bullnose)
• lesions acquired through rooting behavior,
  contaminated with spores
• Carnivores
• pharyngeal anthrax (exposure to spores in
  infected meat)
• Ruminants
• almost exclusively septicemic anthrax
• initiated by GI exposure to spores
• little known of specific steps by which spores
  cross pharyngeal, intestinal mucosa

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PathogenesisCapsule

• Key aspect of virulence
• Nontoxic, serves as an impedin impedes
  phagocytosis
• Vegetative cells released by dead/ dying
  macrophages protected from further phagocytosis
  by capsule
• Polymer of D-glutamic acid
• production enhanced by Na bicarbonate
• Nonencapsulated isolates essentially avirulent
• basis for active immunization of animals against
  anthrax
• Capsule gene is plasmid-borne

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PathogenesisSpores

• Rare in blood and internal organs
• Sporulation inhibited by CO2 (in carcasses)
• Form in well aerated cultures
• Vegetative phase killed by heat, carcass
  autolysis

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Pathogenesis

• Spores engulfed by, germinate in macrophages
• Vegetative cells escape from phagosome, replicate
  in cytoplasm
• Infection may remain localized (eg, cutaneous
  anthrax)
• Local antiphagocytic effects of toxins, capsule
  encourage spread to LN (eg, gastrointestinal
  anthrax)
• Bacterial multiplication in LN gt toxemia,
  bacteremia (especially in pulmonary anthrax)

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Pathogenesis

• Evidence for toxin production
• antibiotic-mediated termination of late-stage
  bacteremia in guinea pigs did not prevent death
• toxin isolated from plasma was lethal IV,
  edemagenic ID
• activities neutralized by antisera
• Three proteins purified edema factor (EF, or
  Factor I), protective antigen (PA, or Factor 2),
  and lethal factor (LF, of Factor 3)
• Mimic features of infection

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Pathogenesis

• PA interacts with LF or EF, binds to membrane
  receptor
• LF, EF ranslocated to cytosol
• PA is major immunogen in vaccines
• Edema due to adenylate cyclase activity of EF
• catalyzes production of intracellular cAMP
• regulated by eukaryotic calcium-binding protein
  calmodulin
• may increase susceptibility by disrupting
  cytokine response of monocytes and suppressing
  neutrophil function
• Lethal factor zinc metalloproteinase
• cleaves kinases, disrupts signal transduction
• lyses macrophages

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Toxin Activity Factors I, II, III
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Therapy of Anthrax

• Ciprofloxacin, doxycycline, penicillins
• Therapy must be administered early, continued for
  weeks
• Point of no return 12 hr antemortem
• guinea pigs inoculated ID
• streptomycin Rx before number reached 3 x 108
  CFU/ml course of disease reversed, guinea pigs
  survived
• Rx administered after 3 x 108 death, in spite
  of greatly reduced number of bacteria

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Bacillus anthracis in BW/BT

• Stability of spores, transmission by respiratory
  route
• High mortality of resulting disease
• 50 kg spores released upwind of city of 0.5
  million people
• 220,000 cases of anthrax
• 95,000 deaths
• Agricultural bioterrorism
• Germans (WWI) Allied horses (Argentina, US,
  Romania, France)
• British (WWII)
• drilled holes into pelleted dairy cattle feed
• inserted capillary tubes filled with anthrax
  spores
• intended to drop from planes (never done)