Gram Positive Bacilli. Grow in aerobic conditions. On gram stain Bacillus anthracis are longer and more deeply staining.
They are spore forming bacteria. B. anthracis causes anthrax.
This disease is common in animals and rare in humans.
In humans disease occurs in three main forms, as cutaneous, pulmonary and gastrointestinal.
In 2001, pulmonary and cutaneous anthrax occurred in USA.
By sending spores of the organism through a mail, the outbreak was caused.
In that outbreak there were eighteen (18) cases and five (5) deaths.
Important properties
anthracis has an anti-phagocytic capsule. It is composed of D glutamate capsule.
It is non-motile.
In this organism anthrax toxin is encoded on a plasmid and the polyglutamate capsule is encoded on a different plasmid.
Transmission
Transmission of this organism occurs as spores. Spores persist in soil for years.
Most of the times humans are infected through trauma to the skin and causes cutaneous disease.
Normally these spores found on animal products, such as hides, bistles and wool.
Spores can also be inhaled into the respiratory tract.
Pulmonary anthrax occurs when spores enter into the lungs.
Gastrointestinal anthrax occurs when spores are ingests. Normally it happens via contaminated meat.
Usually pulmonary anthrax is not transmit from person to person.
It may occur in severe pulmonary disease.
After entering into the lungs, the organism moves rapidly to the lymph nodes of mediastinum. It causes haemorrhagic mediastinitis.
As this organism leaves the lung rapidly, usually it is not transmitted by respiratory route to others.
Pathogenesis
Primarily two exotoxins are produced by these organisms. They are known as anthrax toxins.
Two toxins are
- Edema factor
- Lethal factor
Each toxin consist of two proteins as A and B subunits.
- B subunit is the protective antigen.
- A subunit is the active subunit which has enzymatic activity.
Clinical Findings
In cutaneous anthrax typical lesion is a painless ulcer with a black crust or scab.
In x-ray pictures there are no identifiable changes of pneumonia though lungs are infected.
Mediastinal widening can be seen on chest x-rays. It is one of important diagnostic feature.
Life threatening complications of this organism are haemorrhagic mediastinitis and haemorrhagic meningitis.
Gastrointestinal anthrax shows symptoms like vomiting, abdominal pain and bloody diarrhea.
Laboratory Diagnosis
anthracis is a large gram positive rod that has square ends. Frequently they found in chains.
Spores are usually not seen in smears when high concentrations of nutrients are present in tissues.
In culture B. anthracis grows aerobically and anaerobically.
They are facultative anaerobesand they grow in temperatures range from 12–45ºC.
Optimum growth can be seen in 35–37ºC. Best spore formation is seen in temperatures ranging from 25–30ºC.
Colony morphology
Blood agar
anthracis produces non haemolytic or slightly haemolytic , large colonies, 2–5 mm in diameter, grey-white, irregular colonies with wavy edges.
Broth cultures
They do not usually turbid, but they often show a thick pellicle and a sediment in broth cultures.
Gelatin stab culture
These cultures are occasionally used for the identification of B. anthracis as the reactions are very slow.
B. anthracis slowly liquefies the gelatin along and out from the line of inoculation.
It gives a treelike pattern which are formed by the liquefaction lines of B. anthracis.
It is easy to identify B. anthracis microscopically by their morphological appearance than by this method as the reactions are very slow.
Polymerase Chain Reaction (PCR) can be used for the rapid diagnosis of this organism.
Direct fluorescent antibody test is also can be taken as another rapid diagnostic procedure.
It detects the antigens of the organisms in the lesion.
Other serological tests also can be used for the diagnosis of the organism such as ELISA.
It is useful to diagnose antibodies in serum.
Treatment
Ciprofloxacin is the drug of choice.
Alternative drug for the treatment is Doxycycline.
There are no resistant strains have been recognized clinically.
Prevention
In 2001 Ciprofloxacin plus Doxycycline used as prophylaxis drug for the people who exposed during the outbreak in the United States.
There is a vaccine for high risk people to immunize them with cell- free vaccine which is containing purified protective antigen as an immunogen.
Incineration of the animals that die due to anthrax infection will prevent the soil from becoming contaminated with spores.
No responses yet