Bacillus Anthracis Flashcards
1
Q
Bacillus Anthracis
Overview
A
- G+
- Rod
- Aerobic & Facultative anaerobic
- Non-motile
- Form endospores
2
Q
B.anthracis
Encounter
A
- Main encounter is through Animal products contaminated w/ endospores.
- Soil bacteriumm
3
Q
B.anthracis
Entry
A
- Inoculation into break in skin
- Inhalation
- Ingestion (rare)
4
Q
B.anthracis
Spread
A
- Point sources
- NO person to person spread
5
Q
B.anthracis
Damage
A
- Mediated by toxin
6
Q
B.anthracis
Diagnosis
A
- Gram stain
- Colony morphology of clinical specimen culture
- Capsule presence
- Serological tests
- PCR
7
Q
B.anthracis
Treatment and Prevention
A
- Combination therapy with Ciprofloxacin or Doxycyclin and a second antibiotic
- Prevention via vaccination of Livestock
8
Q
Endospore
A
- Dormant, non-reproductive structure, allows bacterial survival in harsh environmental conditions.
- 1 spore/cell
- Highly resistant to temperature, chemical disinfectants, dessication, radiation, lysozyme.
- Protoplast carries the material for future vegetative cell
- Cortex provides heat and radiation resistance
- Spore wall provides protection from chemicals & enzymes
9
Q
B.anthracis
Pathogenesis
A
- The ID50 of B. anthracis not known.
- Rely on primate data
- LD50 determined to be about 8,000-10,000 spores or .08-.5 micrograms
- Inhalation of about 1,000 spores (.01g) can cause inhalation anthrax
- 100,000 times deadlier than the deadliest chemical warfare agent
- If treatment begins 48 hrs after symptoms, mortality still ~95%
10
Q
Virulence Factors (Strutural)
Capsule
A
- Glycocalyx
- Sticky, gelatinous polymer external to cell wall
- Made up of poly D-glutamic acid
- Non-toxic on its own
- Only encapsulated B. anthracis virulent
- Prevents opsonization and phagocytosis &
- Inhibits complement activation
- Genes required for capsule synthesis located on pX02, a 95 kbp plasmid.
- capBCADE operon encodes capsule biosynthesis genes
- regulated by gene product of acpA and acpB
- capsule production is abolished ΔacpA ΔacpB double mutant.
- regulation
11
Q
Virulence Factor
Toxins
A
- 3 Separate toxins:
- Protective antigen (PA)
- Edema factor (EF)
- Lethal factor (LF)
- Make up 50% of proteins in the organism
- Individually all are non toxic.
- Work by AB model:
- Protective Antigen forms a pore. (B)
- Lethal Factor and Edema Factor have toxin activity
- PA+LF —> lethal activity
- EF+PA —> edema
- EF+LF —> inactive
- PA+LF+EF —> edema & necrosis; lethal
12
Q
Virulence Factor:
Toxin - Protective Antigen (PA, PA83, 83kDa, pag)
A
- Binds to receptor: either tumor endothelium marker-8 (TEM8) or capillary morphogenesis protein 2 (CMG2)
- AKA: Anthrax Receptor 1 and 2 .
- Cell surface furin cleaves PA83 to PA63 and PA20
- PA63 can multimerize into heptamers.
- Multimers can interact w/ either EF of LF.
- Endocytosis brings PA heptamer complexed w/ EF or LF into the cell.
- The low pH of the endosome causes a confirmation change in PA, allowing pore formation.
- EF or LF enter the cytoplasm
13
Q
Virulence Fator:
Toxin - Edema Factor (ED, 89 kDa, cya)
A
- EF is a Ca2+ and calmodulin dependent adenylate cyclase
- Increases the level of cAMP in the cell up to 1000x.
- This upset osmotic balance of the cell causing rapid efflux of electrolytes and water.
- Efflux of fluid leads to edema (swelling) of affected tissues and tissue destruction.
14
Q
Virulence Factor:
Toxin - Lethal Factor (LF, 87 kDa, lef gene)
A
- Affects only macrophages
- LF is a Zn2+-dependent metalloprotease that snips off the N-terminus of mitogen-activated protein kinase kinases (MAPKK).
- Interferes w? cell signaling pathways, preventing normal macrophage function, and eventually leads to apoptosis of the macrophage.
15
Q
Toxin Regulation
A
- all three on plasmid px01
- large plasmid
- all three genes + regulated by AtxA
- AtxA is located on same plasmid
- ΔatxA mutants do not express any of the three toxins
- also + regluates acpA&B (capsule formation)
- transmible plasmid
