医学微生物学
Medical Microbiology
病原生物学教研室
Department of pathogenic Biology of
Gannan Medical University
张文平
Anaerobic bacteria
Clostridium Tetani
Structure
 anaerobic gram-positive rod that forms
terminal spores
 motile with peritrichous flagella
 colonies often swarm on agar plates
 does not produce acid from glucose
 contains a plasmid that produces a toxin
called tetanospasmin
Pathogenesis
Tetanospasmin is
responsible for
the infamous
toxemia called
tetanus.
two toxins
 tetanolysin,
a hemolysin that
is inactivated by
cholesterol and
has no role in
pathogenesis.
 tetanospasmin,
a spasmogenic toxin
responsible for the
classical symptoms of
the disease.
Tetanus Toxin (tetanospasmin) (LONG)
single polypeptide chain (called the progenitor toxin) cleaved
into a heavy chain (fragment B) and light chain (fragment A)
Fragment B binds to the receptor of nerve (ganglioside)
The A fragment has toxic (enzymatic) activity.
It is transported within the axon and across synaptic junctions
until it reaches the central nervous system. There it becomes
rapidly fixed to gangliosides at the presynaptic inhibitory motor
nerve endings, and is taken up into the axon by endocytosis. The
effect of the toxin is to block the release of inhibitory
neurotransmitters (glycine and gamma-amino butyric acid) across
the synaptic cleft, which is required to check the nervous impulse.
sardonic smile (risus sardonicus)
lockjaw
Rigid paralysis
Diagnosis
 Diagnosis of tetanus is obvious in advanced
cases.
 The patient should be treated on a clinical
basis without waiting for laboratory data.
Treatment and Control
 Treatment depends on
early diagnosis and the
use of Human tetanus
immunoglobulin
(HTIG) before a lethal
amount of toxin
becomes fixed to
neural tissue.
.
 Control:
Injections of
tetanus toxoid are
prophylactic
Clostridium perfringens
Pathogenesis
 Produces several tissue degrading enzymes
(including lecithinase [α－toxin],
proteolytic and saccharolytic enzymes).
 Necrosis and destruction of blood vessels
and the surrounding tissue result.
 This creates an anaerobic environment in
adjacent tissue and the organism spreads
systemically.
Diseases
 Gas gangrene,
once initiated,
may spread and
cause death
within hours.
Diseases
 A significant cause of
food poisoning by
enterotoxin producing
strains.
Diagnosis
 Nagler reaction:
exploits the action of its lecithinase.
 On the egg yolk medium, colonies are
surrounded by zones of turbidity, and the
effect is specifically inhibited if C.
perfringens
antiserum
containing
αantitoxin is present on the medium.
stormy fermentation
Nagler reaction
Clostridium Botulinum
Morphology
 a large
anaerobic
bacillus that
forms
subterminal
endospores
Pathogenesis
Botulinum Toxin
(neurotoxin)
 heat-labile(boiling)
 the most potent toxin
 The botulinum toxin is specific for
peripheral nerve endings.
 The toxin binds to the motor neuron and
prevents the release of acetylcholine which
is required for a nerve to simulate the
muscle.
 flaccid paralysis
Diagnosis
 Food-borne Botulism :  Infant Botulism :
blurred vision, inability
constipation and weak
to swallow, difficulty
sucking ability and
in speech, descending
generalized weakness
weakness of skeletal
muscles and respiratory
paralysis
Control and Treatment
 A multivalent toxoid
 Treat: intravenous
evokes good protective
injection of antitoxin
antibiody response.
 Once the botulinum
toxin has bound to
nerve endings, its
activity is unaffected
by antitoxin.
endogenous versus
exogenous infection
 Most anaerobes in the normal flora are non-spore
formers and anaerobic infections often occur from
this source.
 Non-spore-formers rarely produce exotoxins in
contrast to spore-formers.
 Contamination of wounds can also occur with
anaerobic spore-formers (e.g. clostridia) which are
common in the environment (e.g. soil).