Following organisms are main
cause of food infection and intoxication both in human and animals.
•
Listeria
monocytogenes
•
Campylobacter
jejuni
•
Clostridium
botulinum
•
Clostridium
perfringes
•
Bacillus cereus
•
Vibrio cholera
Listeria monocytogenes
Listeria is
the name of a bacteria found in soil and water and some animals, including
poultry and cattle. It can be present in raw milk and foods made from raw milk.
It can also live in food processing plants and contaminate a variety of
processed meats.
Characteristics of organism:
•
Gram positive rods
•
Faculative anaerobe
•
No spores
•
No capsule
•
Motile 10-25o C
•
Closely related to Bacillus, Clostridium,
Enterococcus, Streptococcus and Staphylococcus
•
Genus has 6 species-- L. monocytogenes and L.
ivanovii are pathogenic
•
Major public health concern because:
–
Severe, non-enteric nature of the disease:
–
High case fatality rate à can be as high as
20-30%
–
Long incubation time
Risk
groups
People with following problems are risk on listeria
infection by food.
•
Pregnant women and neonates
•
Elderly
•
Immunocompromised or debilitated people:
•
Malignancy, antineoplastic treatment,
immunosuppressed, chronic liver disease, collagen diseases (lupus), diabetes,
AIDS
•
Older adults.
Habitat
and sources
L.monocytogenes is widely distributed in nature – in soil,
in coastal waters, and in a variety of animals and birds. Moreover many foods
have been implicated but foods marketed as refrigerated and ready to eat
are the ones that have been associated with most of the outbreaks.
Food Sources
of L.monocytogenes
•
Ready-to-eat deli
meats and hot dogs.
•
Refrigerated pâtés or
meat spreads.
•
Unpasteurized (raw)
milk and dairy products.
•
Soft cheese made with
unpasteurized milk, such as queso fresco, Feta, Brie, Camembert.
•
Refrigerated smoked
seafood.
•
Raw sprouts.
•
The organism is beta hemolytic and is easily confused
with b
hemolytic streptococci. Listeria may
also grow in short chains. Do catalase
test!
Growth
and Laboratory Characteristics
•
Facultative anaerobe
•
The organism is b-hemolytic.
•
It is catalase positive
•
It is a gram
positive rod
•
It is psychrotropic
•
The organism is motile
Symptoms
The symptoms
of listeriosis include fever, muscle aches, and sometimes nausea or diarrhea.
If infection spreads to the nervous system, symptoms such as headache, stiff neck,
confusion, loss of balance, or convulsions can occur. But infected pregnant
women may experience only a mild, flu-like illness.
Clinical
signs
Clinical signs are similar in all hosts:
–
Perinatal listeriosis
–
Adult listeriosis
Both are disseminated infection often with CNS involvement
•
Neuromeningeal listeriosis in sheep -- Circling
Disease
Human stillborn -- Granulomaosis infantiseptica
•
Brain lesions in sheep
Internalization:
Following are the host factors that are involve in
internalization of organism into host
•
E-cadherin,
•
C-Met
•
Globular C1-q receptor (complement receptors),
•
glycosaminoglycans
•
fibronectin and integrin
Following are the listeria abilities that are involve in
internalization of organism into host
•
Internalin A
•
Internalin B.
•
p60
•
Ami
•
Lap
•
fibronectin binding protein (24.6 kDa).
Internalin
A (InlA)
•
Binds to E-cadherin in the adherens junction,
triggering actin cytoskeleton rearrangements via association with catenins
Vacuole
formation, proliferation and spread:
•
phagosome formation, lysis and release
Listeria hemolysin Hly (also
known as listeriolysin or LLO)
•
Listeria phospholipases: PlcA and PlcB
(phospholipase C A and B):
Phagocytic
Vacuole formation
•
Phagosome acidifies
•
Lysosome fusion inhibited
Escape
from the Phagocytic Vacuole
•
Listeria hemolysin, (Hly, Listeriolysin, LLO),
•
Cholesterol dependent, pore forming weak
cytolysin
•
Listeria phospholipases: PlcA and PlcB
(phospholipase C A and B)
•
Role in escape from the phagosome
•
Escape from the double membrane vessicle in
cell to cell spread
•
Subvert host cell signalling pathways
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