Listeria monocytogene
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Disease characterized by bacteremia and meningitis
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Affects neonates and immunocompromised hosts
Listeria monocytogenes is a zoonoses. Carried by some animals.
In many foods (cabbage, milk products, soft cheese, pasteurized milk,
sliced dale meats and cheese). Mexican style soft cheese
has been implicated in a large out break of listeriosis.
Can grow at refrigerator temperatures.
- Gram positive rod
- Beta hemolytic
- Catalase positive
- Motile at 25 degree centigrade (tumbling motility/umbrella motility)
- Non-spore forming rod
Susceptible hosts
- Newborns
- Elderly
- Immunocompromised.
- Malignancy
Access to humans
Exposure to contaminated food.
Transplacental infection (mother to infant)
- Invasion of bacteria into intestinal crypt cells, macrophages, M cells
mediated by internalin protein.
- Bacteria enter cell in a vacuole and escape by producing listerolyisn,
a cytolysin similar to streptolysin O
- Listeriolysin mediates escape from the membrane bound vacuole into
the cytosol. Hemolysins hydrolyze host cell membranes.
- Listeria is able to
manipulate host cell action (actin) to propel it into pseudopods that extend to adjacent
host cells. Thus, listeria can spread from cell to cell with minimal contact
with the host immune system.
Human defences
- Requires cellular immunity with activated macrophages to resolve
infection with Listeria
- Macrophages ingest and kill these intracellular pathogens.
Suppression of cell mediated immunity due
to cyclosporine, azathioprine and prednisone. Azathioprine, cyclosporine and glucocorticoids suppress
the ability of macrophages to ingest and kill intracellular pathogens in this
patient.
Listeria is able to
manipulate host cell action (actin) to propel it into pseudopods that extend to adjacent
host cells. Thus, listeria can spread from cell to cell with minimal contact
with the host immune system.
Clinical diseases
Causes bacteremia and meningitis.
Diagnosis
- Culture: Isolate typical colonies from blood, CSF, wounds or
stool cultures
- CSF findings in this patient: The mononuclear pleocytosis, elevated protein
and low sugar are consistent with meningitis due to Listeria.
Other useful evaluations
- The CT suggests an
encephalitis which Listeria has a propensity for causing in an immunosuppressed
patient.
Therapeutic strategy
- Ampicillin or penicillin are ideal.
- Short courses may be associated with
relapse hence at least 4 weeks of treatment is recommended.
- The ability of
Trimethoprim/Sulfamethoxazole to penetrate intra cellularly may offer an
advantage in the treatment of Listeriosis.
Prevention
Only by not being exposed to contaminated food?
Other clinical infections with these organisms
- Neonatal infections
- Puerperal infections
- Granulomatosis infantiseptica