Bacillus anthracisAmanda RussellAnna Bossert

Taxonomy

•Kingdom: Bacteria•Phylum: Firmicutes•Class: Bacilli•Order: Bacillales•Family: Bacillaceae•Genus: Bacillus•Species: anthracis

Basic Facts• Zoonotic Disease: usually

carried by animals, can be transmitted to human hosts under natural conditions

• Rod-shaped• monomorphic• Endospore-forming, remain

viable in soil and animal products for decades

• Gram-positive• Aerobic respiration• Exotoxin producing• Grows best at 24-40⁰C• Incubation period: 1 to 15

days• Three forms: inhaltion,

gastrointestinal, cutaneous

Virulence Factors•Encoded on two plasmids

▫One encodes for the synthesis of a polyglutamyl capsule (inhibits phagocytosis by macrophages)

▫Other bears genes encoding for the synthesis of exotoxins

•Exotoxins: three proteins▫Protective antigen▫Edema Factor: adenylate cyclase activity,

increases cAMP, leads to cytoplasm loss after forming an edema

▫Lethal Factor: interferes with transcription factor in genome (NfkB) which regulates immunity genes. Once these are no longer transcribed, immune response of macrophages will fade.

General Mode of Infection• B. anthracis spores enter the body (lungs,

skin lesion, gastrointestinal) and germinate, giving rise to the vegetative form• The bacterium begins to produce

capsules containing exotoxins, which will help evade the host’s immune system• The PA portion will bind to receptors on

the membrane of macrophages, when seven complexes are combined they form a ring. This ring will pierce through the membrane and the macrophage will shuttle in the complex as an endosome

General Mode of Infection cont.•The PA molecules will form a pore that

pierces the endosome membrane, releasing the EF and LF into the cytoplasm of the macrophage

•EF and LF essentially kill the macrophage, and release the contents of the macrophage to the outside.

•The endosome enzymes that were released will degrade surrounding tissues, resulting in the common symptoms of anthrax.

Cutaneous Anthrax

•B. anthracis comes into contact with a skin lesion, or cut.

•The spores germinate, producing bacteria, which produce exotoxins to evade the macrophages

•Infection is manifested in a painless ulcer with a necrotic (dead) center

•Transmission: coming in contact with infected animals or their products through a skin lesion

Symptoms of cutaneous anthrax• Boil-like skin lesion

forming a painless ulcer• Swelling of the lymph

glands• Fever• Headache

Inhalation Anthrax•The spores are inhaled and lodge in the

alveolar spaces•Alveolar macrophages engulf the spores.•Spores germinate within macrophages

after failed phagocytosis•Bacteria proceed to lymph nodes and

spread into bloodstream, where they begin to release the exotoxins

•Transmission: inhaling the spores of B. anthracis

Symptoms of Inhalation Anthrax• Initial symptoms: sore

throat, mild fever, muscle aches

• Severe difficulty breathing• Septic shock• Development of meningitis• Respiratory failure

resulting in death

Gastrointestinal Anthrax• Spores are consumed after eating undercooked meat• Spores can evade stomach acid due to their capsule• Once in the digestive tract, they begin to germinate

and produce bacteria, which release exotoxins• After the macrophages have been lysed, the

endosome enzymes begin degrading intestinal walls, allowing the bacteria to spread directly into the bloodstream

• Transmission: Digesting undercooked meat containing spores

Symptoms of Gastrointestinal anthrax•Serious gastrointestinal difficulty•Nausea•Fever•Abdominal pain•Vomiting of blood•Severe bloody diarrhea•Acute inflammation of intestinal tract•Loss of appetite

Diagnosis•A diagnosis can be made by taking a

smear of a skin lesion (if cutaneous anthrax) and gram-staining the sample.

•Blood tests that show encapsulated, broad, gram-positive bacilli

•Cultures: large, flat, nonhemolytic colonies, non-motile, will test positive for catalse, positive for capsule production

•Confirmatory Diagnosis: Serological tests for toxins at reference laboratories

Transmission

•Bacillus anthracis is transmitted mainly through the contact of infected animals or their products, and humans, resulting in cutaneous anthrax

• It cannot be spread from human to human.•2001: Anthrax was sent in the form of a

powder in letters, when the recipient of the letter opened them and inhaled the spores, they became infected. 5 out of 22 died.▫Biological Warfare Debate

Prevalence• In the past, anthrax was found all over the world.• Now, this bacterium is found mainly in

underdeveloped countries lacking the means of disease control; such as the Middle East, Africa, Australia, southern and eastern Europe, South and Central America, Asia

• It is not common in the United States, although small outbreaks periodically occur in agricultural areas on animals.

• The last outbreak resulted in the death of 5 out of 22 people in 2001.▫ 1987: 20 out of 22 had died

• 2,000 – 20,000 human outbreaks annually

Susceptibility

•All warm-blooded animals are susceptible to anthrax, especially herbivores▫Other domesticated animals such as horses

and mules may also contract the disease.

Treatment

•Cutaneous / gastrointestinal▫Antibiotic therapy for 7 – 14 days

•Inhalation▫Antibiotic therapy for 30 days if used alone▫If vaccine is available, antibiotics can be

discontinued after 3 doses of vaccine

Vaccine

•Anthrax Vaccine Adsorbed (AVA)▫6-dose series at 0,2,4 weeks and 6,12,18

months▫Annual booster injections to maintain

immunity•Who receives vaccine?

▫Animals, mainly cattle▫People with high occupational risk

Military, people close to an outbreak

Prevention• Decontamination

▫Wash down with anti-microbe effective soap▫Boil articles that came in contact with infected

hosts▫Chlorine▫Burning articles

• Early detection▫USPS installed BioDetection System

• Antibiotics▫Penicillin▫Doxycycline

Current Research

•New research has found that extracellular metalloproteases may play a role in the survival of the bacterium▫Aid in degradation of the LL-37 peptide. ▫Other bacillus species showed no

resistance to this peptide

Current Research cont.

•Anti-protective antigen antibody has been shown to suppress the vegetative form of B. anthracis before it sporulates.

Current Research cont.

•Research has also shown a new technique in identifying anthrax spores before a new outbreak occurs.▫Microwave-Accelerated Metal-Enhanced

Fluorescence (MAMEF) (Metal-enhanced flulow power microwave heating) is used to accelerate DNA hybridization

▫The DNA of the B. anthracis spores was detected almost immediately.

References• http://www.ncbi.nlm.nih.gov/sites/entrez?

Db=pubmed&Cmd=ShowDetailView&TermToSearch=17955147&ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

• Microbiology Lecture Textbook• http://www.cdc.gov/• http://www.nlm.nih.gov/medlineplus/anthrax.html• http://pathport.vbi.vt.edu/pathinfo/pathogens/Bacillus-anthracis.html• http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?

id=191218&lvl=1• http://www.ncbi.nlm.nih.gov/sites/entrez• http://www.bt.cdc.gov/agent/anthrax/lab-testing/#references