Although bacteria are associated with disease, only a few species are disease-producing or pathogenic for healthy individuals . Of greater concern are those organisms that, if presented with the correct set of conditions, can cause disease, i.e. opportunist pathogens. Examples include Staphylococcus epidermidis.....
BACTERIAL TOXINS
Although bacteria are
associated with disease, only a few species are disease-producing or pathogenic
for healthy individuals . Of greater concern are those organisms that, if
presented with the correct set of conditions, can cause disease, i.e.
opportunist pathogens. Examples include Staphylococcus
epidermidis, a beneficial organism when present on the skin (its normal
habitat) yet potentially fatal if attached to a synthetic heart valve, and Ps. aeruginosa, a non-pathogenic
environmental organism but again potentially lethal in immunocompromised
patients.
The pathogens cause host
damage in a number of ways. In most cases pathogens produce a variety of molecules
or factors that promote pathogenesis, among which are the toxins: products of
bacteria that produce immediate host cell damage. Toxins have been classified
as either endotoxin, i.e. cell wall-related, or exotoxin, products released
extracellularly as the organism grows.
Endotoxin is the lipid A
component of LPS. It possesses multiple biological
properties including the ability to induce fever, initiate the complement and
blood cascades, activate B lymphocytes and stimulate production of tumour
necrosis factor. Endotoxin is generally released from lysed or damaged cells.
Care must be taken to eliminate or exclude such heat-resistant material from
parenteral products and their delivery systems through a process known as de-pyrogenation.
Most exotoxins fall into
one of three categories on the basis of their structure and activities. These
are the AB toxins, the cytolytic toxins and the superantigen toxins. The AB
toxins consist of a B subunit that binds to a host cell receptor and is also
covalently bound to the A subunit that mediates the enzymic activity responsible
for toxicity. Most exotoxins (e.g. diphtheria toxin, cholera toxin) are of the
AB category. The cytolytic toxins such as haemolysins and phospholipases do not
have separable A and B portions but work by enzymatically attacking cell
constituents, causing lysis. The superantigens also lack an AB type structure
and act by stimulating large numbers of immune response cells to release
cytokines, resulting in a massive inflammatory reaction. An example of this
type of reaction is Staphylococcus aureus-mediated
toxic shock syndrome.
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