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Microorganism toxins
Chain of infection
-reservoir, where an infectious agent normally lives, grows and multiplies, reservoirs include
humans, animals and the environment
- portal of exit, is the path by which the pathogen leaves its host
- modes of transmission, describe the way in which an infectious agent is transmitted from its
natural reservoir ro a susceptible host, transmission occurs by many routes and can be
direct or indirect
- portal of entry, the way in which a pathogen enters a susceptible host, the portal of entry
must provide access to tissues in which the pathogen can multiply or a toxin can act
-host, susceptibility of a host depends on genetic or constitutional factors, specific immunity
and nonspecific factors that affect an individual's ability to resist infection
Microorganism toxins
The pathogen may actively secrete exotoxins which aid in pathogen entry, spread, or
defense against the host
...

Exotoxins consist of a functional and a binding domain
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Microbes that multiply in cells cannot afford to cause
serious damage at too early a stage, and such toxins therefore tend to be less prominent in
intracellular infections
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Bacteria may produce enzymes to promote their survival or spread, eg
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Toxins may damage or destroy cells and are then known as hemolysins
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Toxins may enter cells and actively alter metabolic machinery
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When the binding B subunit binds to receptors on the cell
membrane, the functional A subunit, or the whole toxin-receptor complex, is taken into the
cell by endocytosis and the A subunit is activated
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by formaldehyde) without altering their antigenicity, and the
resulting toxoids are among the most successful vaccines
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For example, the
plant toxin ricin, the A subunit can be attached to a monoclonal antibody to make it a specific
poison for tumour cells
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Spores of ​C
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When foods are canned or preserved without adequate sterilization (often at home),
contaminating spores survive and can germinate in the anaerobic environment leading to the

formation of toxin
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While not destroyed by digestive enzymes
the toxins are inactivated after 30 minutes at 80 degrees celsius
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Botulinum toxins have a characteristic two subunit structure, a functional A domain and a
binding B domain
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The toxin affects peripheral nerve endings at the neuromuscular
junction, blocking presynaptic release of acetylcholine
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Botulinum toxins are extremely potent and active at low doses
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Then respiratory and cardiac muscles are
affected
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There are three forms of botulism; food-bourne botulism, infant botulism, and wound
botulism
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In infant botulism the organisms are ingested and multiply and
elboarte toxin in vivo
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botulinum s​ pores
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Laboratory diagnosis involves demonstrating the presence of toxin in clinical
specimens or food or culturing the bacteria
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Culture of faces or wound exudate for ​C
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Since the specific ​C
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Supportive therapy may include mechanical ventilation, due
to difficulty in breathing, and intravenous and nasogastric nutritional support, due to
dysphagia
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Tetanus
Tetanus is caused by the bacteria ​clostridium tetani
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tetani ​ produce endospores within
their cells, enabling them to survive in adverse conditions
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when environmental conditions change or when nutrients are
exhausted
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Tetanus spores are widespread in soil and originate from the faeces of domestic animals
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Tetanus toxins are
extremely potent and active at low doses
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The B subunit binds to ganglioside receptors on nerve cells
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This allows the excitatry transmitter
to continuoulsy stimluate the mototr neurons, causing spastic paralysis
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The diagnosis if tetanus is clinical
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The wound should be excused if necessary
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Muscle relaxants are used
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Tetanus is a vaccine preventable disease
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cholerae
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The disease remains endemic in South-East
Asia, parts of Africa, and South America
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cholerae ​ is a free-living inhabitant in fresh
water, and only causes infection in humans
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The disease is spread via contaminated food
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​V
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Only O1 and O139 serogroups cause epidemic cholera
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E1 Tor differs from classical ​V
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The O139 strain
infects O1-immune individuals
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cholerae O
​ 139 originated from E1 To O1 biotype and then
acquired a new capsular O antigen by horizontal gene transfer from a non O1-strain, but is
otherwise identical to O1 E1 Tor
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The symptoms of cholera are due to the production of an enterotoxin in the gastrointestinal
tract
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The A subunit
activates adenylate cyclase causing intracellular cAMP to rise, resulting in chloride secretion

and secretory diarrhoea
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​V
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After an incubation period of 2-3 days, ​V
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The severe watery non-bloody diarrhea is known as rice
water stool because of its appearance and can result in the loss of 1 litre of fluid every hour
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Culture is necessary to diagnose sporadic or imported cases of cholera and carriers
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ETEC infection
is a possible differential diagnosis
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Antibiotics reduce the duration of excretion of ​V
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Clean drinking water and adequate sewage disposal are fundamental to the prevention of
cholera
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Shigellosis
Shigellosis is a gram-negative rod
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The main route of transmission of shigella
pathogens is the fecal-oral route
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There are four subgroups of shigella; ​Shigella sonnei w
​ hich causes mild infection, ​S
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boydii, ​and ​S
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Shigella has a large
virulence plasmid that encodes secreted proteins acting on colonic epithelial cells that
damage the epithelial lining as well as acting on the host immune response
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​S
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After an incubation period of 1-4 days, shigellosis presents
clinically with severe lower abdominal cramps and fever
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The disease is usually self-limiting, but dehydration can
occur in the young and the elderly
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coli​
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Shigellosis is treated through rehydration
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Staphylococcus aureus

Enterotoxigenic strains of ​S
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The classic
serotypes are enterotoxins A-E, with A being the most commonly associated with
food-bourne intoxication
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​S
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Their effect on the central nervous
system results in severe vomiting within 3-6 hours of consumption
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Recovery within 24 hours is usual
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Food may be contaminated with enterotoxins by human carriers
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The bacteria grow at room
temperature and release toxin
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Enterotoxin have been detected by a latex agglutination test, but immunoassays are more
sensitive

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