Soil Pathogens Flashcards
Anthrax
-A disease that primarily affects livestock (particularly cattle) by can infect
humans.
-It is caused by Bacillus anthracis, a capsulated gram-positive bacterium that produces endospores upon exposure to the environment enabling survival,
in the soil for decades.
Discovery of anthrax
Robert Koch isolated B. anthracis in 1877 and
established that it was the pathogen responsible for
Anthrax. He used this disease to formulate his
famous postulates.
three forms of human anthrax
Cutaneous anthrax
Gastrointestinal anthrax
Pulmonary anthrax
Cutaneous anthrax
Cutaneous anthrax is contacted when
spores are introduced into broken skin
through mechanical damage or flies
Gastrointestinal anthrax
Gastrointestinal anthrax infects intestinal
lesions (animals eat spiky or hard
vegetation which damages the mucosa of
the gut).
Pulmonary anthrax
the inhalation of spores
in dust
Livestock contraction of anthrax
Livestock (or herbivores in the wild) are often infected by grazing on contaminated (spore-containing) soil, carnivores can contract the disease by eating infected animals
Human source of anthrax
Humans commonly contract anthrax from the handling of contaminated animal products (hides, wool,
meat) as a result, cutaneous anthrax is the most common form of the disease in humans.
Major virulence factor of anthrax
Capsule because it prevents killing by macrophages
Cutaneous anthrax mortality rate
Cutaneous anthrax has a lower mortality rate than gastrointestinal and pulmonary anthrax
(approx. 20%) as the infection is initially a local one. If untreated it will spread, and the
individual will die from toxaemia (dissemination of toxins in the blood).
Gastrointestinal anthrax has a mortality rate of
25-60%
Pulmonary anthrax can have a mortality rate of
45-90%
Antharx plasmids
pXO2 encodes for its capsule which is essential for immune evasion.
PXO1 encodes for its toxins: protective antigen (PA), edema factor (EF), and lethal factor
(LF).
Anthrax toxin mechanism
Anthrax toxins are a variant of the A-B toxin system:
1) PA is responsible for the transport of EF and LF into cells. It binds to cell receptors then it is
cleaved by furin, a protease on the surface of the cell to generate a 63kDa protein
fragment. 5 fragments form a heptamer, which form a pore-like structure in the
membrane of the cell.
2) The pore heptamer complex facilitates the transport of EF into the cell. This causes an
increase in cAMP and altered calcium signalling. This alters ion and water transport, which
in turn alters osmolarity within the cell.
3) The pore heptamer complex also facilitates the transport of LF into the cell. This damages
the MAPK signalling pathway and causes apoptosis.
Overall effect of anthrax toxin
Ultimately, the toxins kill immune cells and damage blood vessels leading to fluid
accumulation in tissues, cell death and the release of inflammatory cytokines. Death is from
shock, tissue damage and hypovolemic shock.
Anthrax treatments
If diagnosed in time, anthrax can be treated with antibiotics however, if sufficient
toxins have already been produced in the infected individual, antibiotics are
ineffective.
A vaccine is available and was originally developed by Pasteur. This has significantly
reduced the incidence of anthrax, which was once a significant cause of livestock
mortality.
Anthrax militray usage
The high mortality rate of pulmonary anthrax has led to it being developed as a
bioweapon by Japan and Russia and the UK during and after the second world war.
In 2001 anthrax ‘powder’ was sent to government offices in envelopes in the USA,
leading to several deaths. Bruce Ivins was later found to be responsible for these
bioterrorism attacks.
Tetanus and Gas Gangrene description
Two potentially life-threatening diseases caused by soil-borne clostridia, which are spore-forming
gram-positive anaerobes.
Infiltration and effect of tetani
C. tetani gains access to the body through a soil-contaminated wound, typically a deep
puncture.
Result of C. tetani infection on people is lockjaw. Paralysis extends to rest of body
Tetanus treatment
Tetanus is preventable; the existing vaccine is completely effective, usually lasts for 10
years
Tetanus toxin mechanism
a) Muscle relaxation is normally induced by glycine (G) release from inhibitory interneurons. Glycine acts on the motor
neurons to block excitation and release of acetylcholine (A) at the motor end plate. (b) Tetanus toxin binds to the
interneuron to prevent release of glycine from vesicles, resulting in a lack of inhibitory signals to the motor neurons,
constant release of acetylcholine to the muscle fibers, irreversible contraction of the muscles, and spastic paralysis.
Gas gangrene (myonecrosis)
A potentially fatal infection of deep soft tissue mainly caused by Clostridium perfringens,
where the bacterium enters deep wounds through trauma.
Wounds formed as a complication of diabetes can also become gangrenous. Individuals
with vascular damage and immune impairment are most susceptible.
Grangene disease mechanism
The clostridial organisms produce alpha and theta toxins that cause extensive tissue
damage. The infection can spread quickly, and within a matter of several hours, the patient
may develop overwhelming shock, sepsis, and death.
Grangene disease treatment
Aggressive early treatment with antibiotics and hyperbaric oxygen is usually required.
Amputation of dead tissue may be necessary.
Alpha toxin
Lecithinase (or phospholipase) that breaks down cell membrane resulting in cell death and tissue
necrosis. This toxin is also hemolytic and cardiotoxic.
Beta toxin
Necrosis of tissue
Delta toxin
Hemolysin
Epsilon toxin:
Acts to increase cell membrane permeability; permease.
Iota toxin: Necrosis of tissue
Kappa toxin
Collagenase, gelatinase, necrosis of tissue. Especially leads to destruction of blood vessels and
connective tissue.
Lambda toxin
Protease
Mu toxin
Hyaluronidase
Nu toxin
Deoxyribonuclease, hemolytic and necrosis of tissu
Phi toxin
Hemolysin, cytolysin
Waterborne diseases
Many pathogens can be transmitted via contaminated water whether this is water used for drinking,
cooking washing etc. or recreational water (pools, ponds lakes etc.)
Eg: Cholera, Legionelles
Cholera
Cholera is a potentially fatal gastrointestinal diarrheal disease caused by Vibrio cholerae, a
gram-negative highly motile (flagellated) bacterium
Cholera transmission
Cholera is typically transmitted through
ingestion of (fecal) contaminated water or seafood such oysters or shellfish that have beenexposed to water containing the bacterium.
Vibrio cholerae accumulates in or interacts with phytoplankton and zooplankton which are eaten by shellfish.
location cholera epidemics
Cholera epidemics were once common throughout the world but now, cases are
restricted to developing countries in Africa, Southeast Asia, the Indian subcontinent, and
Central and South America, where proper water treatment is lacking.
The discovery of the source of a major cholera outbreak in London in the 1850’s (the
Southwark and Vauxhall’s Broad-Street water pump) by physician, John Snow, is
regarded as a triumph of epidemiology.
Cholera mechanism of infection
Once ingested, V. cholerae cells are mostly destroyed by stomach acid. Those cells that
survive move to the small intestine and migrate through the mucus layer covering the
epithelium and attach to epithelial cells of the small intestine where they begin to
proliferate and produce the cholera toxin.
Cholera infection symptoms
This results in the production of large amounts of watery diarrhoea (called rice water),
which facilitates the expulsion of progeny bacterial cells from the host into new water
sources.
The enterotoxin causes fluid losses of up to 20 litres (20 kilograms or 44 l b) per person per
day, causing severe dehydration.
The mortality rate from untreated cholera is 25–50 percent
Cholera toxin mechanism
The cholera toxin is a potent A-B toxin. The A
subunit, upon cellular entry, ADP-ribosylates the enzyme Adenylate cyclase, which causes a large increase in cAMP. This prevents Na ion uptake and the hypersecretion of anions and water from the cell
Cholera treatment
Treatment usually requires oral or in severe cases, intravenous hydration therapy with
electrolyte replacement, together with antibiotics.
A vaccine is available.
Legionnaire’s disease (LD) cause
A Non-Communicable Water-borne disease
The causative agent is Legionella pneumophila, a gram-negative bacterium known to be a major waterborne
pathogen in residential water systems such as hot-water tanks, hot tubs and the cooling water systems of air conditioners. It often exists in biofilms in which it is protected from the chlorine present in potable waters.
It also infects and ‘shelters’ within amoeba, which exist within biofilms.
Infected amoeba are reservoirs for Legionella pneumophila.
LD route of infection
The pathogen is inhaled as aerosolized droplets into the lungs, where it is taken up by
resident macrophages.
Those usually at risk are the elderly and people with compromised lung function or those that smoke.
LD mechansim of infection
The interaction of virulent legionellae with phagocytic cells can be divided into several
steps:
* binding of microorganisms to receptors on the surface of eukaryotic cells
* penetration of microorganisms into phagocytes
* escape from bactericidal attack
* formation of a replicative vacuole (a compartment within the cell where bacterial
replication occurs)
* intracellular multiplication and killing of the host cell.
LD effect
This results in a severe, often fatal pneumonia, that is not spread to others.
LD treatment
Legionellosis can be treated with
antibiotics, in particular rifampin
and erythromycin, and
intravenous administration of
erythromycin is the treatment of
choice for life-threatening cases.
Nororvirus
(Norwalk Agent)
(non-enveloped, positive sense RNA virus)
A common viral cause of gastrointestinal illness.
Norovirus symptoms
Symptoms are vomiting, diarrhoea, and malaise, it is rarely fatal.
Norovirus cell type
The virus specifically attacks tuft cells found in the intestinal epithelium. These are a specialized class of chemosensory cells that detect specific molecules made by bacteria and protozoans within the intestine
Norovirus transmission (where its found)
-Noroviruses are easily transmitted from person to person or to food by a faecal-oral route.
-Most common sources of waterborne norovirus outbreaks are well water or recreational waters that have been
contaminated with sewage.
-Often the culprit when mass common-source gastrointestinal illnesses strike people on cruise ships or in longterm care facilities or other group setting.
