Download Gram positive endospore forming rods

Gram positive endospore
forming rods
Clostridium botulinum—anaerobic—adult and infant botulism
Clostridium perfringens—anaerobic—diarrhea
Bacillus cereus—facultatively anaerobic—gastroenteritis
(diarrhea and vomiting)
Why do bacteria form endospores
• Survival of the bacterial species
• Endospores carry the genomic information
of the vegetative cell
Vegetative cells vs. endospores
• Vegetative cells are metabolically active
(taking in nutrients, converting nutrients
into energy and biomass, expelling
wastes, growing and dividing)
Endospores are dormant—metabolically
inactive (but contains the genetic material
of the vegetative cell)
Why are endospores dormant?
• Filled with SASPS (small acid soluble
proteins that protect DNA)
• Has low water activity
• Has relatively few metabolic enzymes
• Surrounded by a tough keratin-like coat
How does being dormant benefit an
endospore
• Can survive the following conditions
drying
high heat
UV irradiation
low pH
high osmolarity
low temperature
Conditions that most vegetative cells cannot
survive
Life cycle of an endospore
• Vegetative cell (unpleasant conditions)
• Veg. cell replicates DNA, forms a septum 1/3 of
the length of the cell and pumps DNA into the
region
• Endospore develops at that site and is finally
surrounded by a tough keratin like coat
• Veg cell dies releasing the mature endospore
• Free mature endospore (pleasant conditions)
• Endospore germinates to become a vegetative
cell
Clostridium botulinum
• Causes botulism (food posioning)
• Causes infant botulism from honey
• Abundant in soil throughout the world
Type A C. botulinum—found in
neutral/alkaline soil west of the Mississippi River
Type B C. botulinum—found in eastern part
of the country
Type C C. botulinum—found in wet soils
(can effect fish)
Botulism cases are rare
• Foodborn botulism—50 cases per
annum usually due to home canning of food
(Type A and Type B) or preserved fish (Type E)
• Infant botulism—100 cases per annum
usually due to spores present in honey that is
introduced to formula
Foodborn botulism—toxin formed
in food
• Canning—endospores are not eradicated
if the temperature is not sufficiently high
• Spores are present in a nutrient rich
environment that is also anaerobic
• The spores germinate and become
vegetative bacteria
• The vegetative bacteria produce botulism
toxin—a potent neurotoxin
Botulism toxin
• Toxin has no taste
• Food is often not spoiled by the bacteria
• A small amount of food with the toxin can
be lethal
• Botulism toxin is heat labile
Infant botulism—(3-20 weeks old)
• Toxin is formed in the infant’s colon
• Honey has a high osmolarity; therefore, the
endospores cannot germinate
• Honey is mixed with infant formula that dilutes
the honey—the infant drinks the solution
• The spores are introduced into the stomach and
move to the colon
• The spores germinate in the colon
• The vegetative cells produce botulism
neurotoxin in the colon
Clinical diseases caused by
botulism neurotoxin (cause)
• Foodborn botulism--12-36 hours after ingestion
toxin travels to different parts of the body
• Botulism toxin binds to acetocholine receptors
on neural cells
• Impulses are not sent from one neural cell to
another
• Muscles (smooth, involutary, motor) are not
stimulated by the neurons and cannot move
• This causes flaccid paralysis of the muscles
Clinical diseases caused by
botulism neurotoxin (effect)
• Flaccid paralysis of muscles
• Cranial nerves are the first affected
double vision/blurred vision
difficulty swallowing
• Muscles in the arms and legs are next to be
affected
• Diaphragm muscles are affected causing
difficulty in breathing
• There is no fever or cell death
• END RESULT:: paralysis and respiratory failure
Treatment
• Deliver antitoxin to the three known botulism
neurotoxin
• The antitoxin binds to the free circulating
neurotoxin and prevents it from binding to
acetocholine receptors
• N.B. Bound neurotoxin cannot be inactivated as
it is already bound to acetocholine receptors
• Supportive therapy—intubation until neurons
regenerate
Infant botulism-diseases and
treatment
• Disease is slow in occurring because toxin cannot be
readily absorbed from the colon
• 2-3 days constipation
• Difficulty swallowing—poor suckling response
• Flaccid baby
• Hospitalization and intubation may be required
• Prognosis is usually good so no antitoxin is required
• N.B. SIDS has been attributed in part to infant botulism
Bacillus cereus
• B. cereus is facultatively anaerobic and
found in every environment.
• Causes abdominal pain and diarrhea
AND/OR
• Nausea/vomiting
Disease caused by B. cereus
• Disease is caused by two toxins
• Enterotoxin—heat stable/proteolysis resistant
--Causes nausea and vomiting
--Found commonly in improperly
stored rice
• Heat labile form
--Causes watery diarrhea as water is not
absorbed in the intestines
--Found commonly in contaminated
meats vegetables and sauces
--Takes longer to get sick as disease is caused as B.
cereus divides in the patients G-I tract