Lecture 8: Bacillus Anthracis

Describe the morphology and important details of the Bacillus spp.

• Large Gram +

• Aerobic

• Spore-forming

• Chain bacilli

The phenotypic and virulence characteristics of Bacillus spp. are encoded on ______

Plasmids

What are the 3 main types of Bacillus spp. we discuss? Of these 3 species which is the only one that is non-hemolytic?

1. B. anthracis

   1. Only non-hemolytic Bacillus

2. B. cereus

3. B. thuringiensis

What is unique about the B. anthracis colonies on blood agar? (use hint if you don’t remember)

They appear as “ground-glass” on the surface of the colony and have irregular edges, often described as “medusa’s head”

Bacillus spp. are very environmentally resistant, which is why they are soil saprophytes. Why are they so environmentally sound?

They produce endospores through a process called Sporulation

What triggers the sporulation of Bacillus spp.?

Environmental cues (Nutrient depletion, pH change, drought)

T/F: Bacillus spp. endospores are metabolically inert

True

What specific type of stain is used to show Bacillus spp. endospores?

Malachite green (then use safranin red as a counterstain)

What is the difference between the vegetative form and the capsule of Bacillus anthracis?

• Vegetative form

  • Large Gram +, non-motile rods

  • Multiplies in the host

• Capsule (Gel layer)

  • Only forms around the vegetative form of the bacteria, and only forms In-VIVO

  • Shields the bacterium from the immune system

B. antrhacis contains 2 plasmids, what are they?

1. pXO1

2. pXO2

T/F: B. anthracis is a critical biological agent, as it has been used as a biological weapon in the past

True

B. anthracis is capable of affecting most mammals, which type of animals are more suscpetible/resistant?

• Herbivores are more susceptible

• Carnivores are more resistant (but still get it)

T/F: B. anthracis is zoonotic

True!

What is the incubation period for B. anthracis?

1-14 days in naturally infected livestock

How does B. anthracis spread in naturally infected animals?

They ingest Anthrax spores from grazing, browsing, drinking, or inhale it 

B. anthracis is “Armed to annihilate host _____ immune defences“

Innate

Virulence factors of B. anthracis are _____ encoded

Plasmid

What are the 3 toxins utilized by B. anthracis, describe each

1. Protective antigen (PA)

   • Binds to the cell receptor and helps internalize the other factors (EF and LF)

2. Edema Factor (EF)

   • Causes edema and impairs immune functions

     • Via adenylate cyclase

3. Lethal Factor (LF)

   • Causes apoptosis of macrophages, PMNs, and vascular endothelial cells

     • Via metalloprotease

Which plasmid encodes them capsule of Bacillus anthracis?

pXO2

The S-layer is different from the other virulence factors  of B. anthracis, in what way (aside from function)?

It is chromosomally encoded

The capsule of B. anthracis is produced in the ___ and is very weakly immunogenic, its main function is to…

• Host

• Prevent phagocytosis (antiphagocytic) and allow the bacteria to survive long enough to induce septicemia

What is the function of the S-layer of B. anthracis?

It covers the peptidoglycans on the cell surface and inhibits the complement pathway

Anthrax toxin causes pathologic effects on the ___________ system

Cardiovascular

T/F: Anthrax is endemic in some regions

True

Describe the environment that best facilitates the survival of B. anthracis spores

• Low lying areas

• High moisture

• Soil is high in calcium and alkaline pH

What environmental condition favors the “perfect storm” for an anthrax outbreak to occur?

Heavy rain/flooding in the spring followed by drought

Which animals are highly susceptible to anthrax? What are the noticeable signs of anthrax in these animals?

• Cattle, sheep, goats

  • Blood doesn’t clot quickly and is dark in color

  • Lack of rigor mortis after death

Which species is resistant to anthrax?

Birds

T/F: When you have a sudden death case of a ruminant, you should perform an autopsy first before reporting

False, you should collect some blood and have it tested

Which substance should be avoided when protecting/quarantining the body of animals who died from anthrax?

Calcium, it protects anthrax spores

The recommended method of carcass disposal for anthrax is ________

Incineration

T/F: B. anthracis is a federally reportable disease

True

What is the best way to protect an animal from anthrax?

Vaccinate the 2-4 weeks prior to pasturing in endemic areas

The vaccine for B. anthracis reduces the virulence in what way?

It removes the plasmid DNA coding for capsule

When treating bacillus anthracis the first drug of choice is ________

Penicillin

Why is B. anthracis such a problem in Siberia? So much so that is dubbed the name “the Siberian Plague”

• vaccine programs not maintained

• A horrible outbreak tied with permafrost meant that the bodies coulnd’t be buried so now it is endemic

T/F: B. anthracis is an ideal biological warfare agent

True

T/F: Survival of B anthracis spores is supported in acidic soils

False, alkaline soils

T/F: Anthrax spores are destroyed by deep burial of infected animal carcasses in the ground

False, incineration is best for destroying spores

T/F: B. anthracis cycles between spore formation in animals and vegetative growth in the environment

False, exists in the environment as a spore, only replicates in animals

T/F: B. anthracis capsule and toxins are chromosomally-encoded

False, they are encoded by plasmids, the S-layer is encoded by chromosomes

T/F: Anthrax causes fatal septicemia and toxemia in domestic and wild ruminants

True

T/F: Outbreaks of anthrax are influenced by climate and geography

True