Bacillus anthracis Amanda Russell Anna 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. anthracisspores 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