GI Infections - Listeria Monocytogenes Flashcards
What type of bacteria is Listeria monocytogenes?
Gram positive rod
What are the sources of Listeria monocytogenes?
Environment: 5% of humans intestinal carriers
- found in at least 37 mammalian species, both domestic and feral,
- least 17 species of birds, some species of fish & shellfish.
- soil, silage, and other environmental sources
Foods: raw milk, cheeses (particularly soft-ripened varieties), ice cream, raw vegetables, fermented raw-meat sausages, raw & cooked poultry, raw meats & raw & smoked fish.
How low is the temperature that Listeria monocytogenes can grow?
3°C
What is the infective dose of Listeria monocytogenes?
Not known but thought to vary depending on individual (> 1000)
Describe the pathogenesis of Listeria monocytogenes
Intracellular pathogen that induces host cell to engulf via the mediation of protein called internalin
- entry via GI epithelial cells within a phagocytic vacuole
Produces listeriolysin O (B-haemolysin) & phospholipases
- permits escape from phagosome (membrane bound vacuole) into cytoplasm & multiply
Produce pseudopods that extend into adjacent host cells to spread cell to cell
Requires cellular actin tails and listerial phospholipase activity
From GI epithelial cells it enters lamina propria into macrophages - carried by lymph or blood to mesenteric nodes, spleen & liver
How does infection by Listeria Monocytogenes differ between the immunocompetent and the immunocompromised?
Immunocompetent: macrophages activated by cytokines (T cell-mediated) – infection removed
Immunocompromised – further spread
What are the symptoms of infection by Listeria monocytogenes?
Variety of clinical presentations:
- Mild flu like to severe illness in pregnancy – can cause premature birth or miscarriage
- Meningitis in newborn
Symptoms appear within 1 to 90 days
What symptoms of infection by Listeria monocytogenes appear in patients who are immunocoompromised?
Septicaemia
Meningitis
Encephalitis
(most common cause of meningitis in transplant patients)
What are the symptoms of non-invasive Listeriosis (Listerial Gastroenteritis)?
Chills Diarrhoea Headache Abdominal pain and cramps Nausea Vomiting Fatigue Myalgia
What are the major risk groups for infection by Listeria monocytogenes?
Pregnant women Foetus Neonates Immunocompromised Elderly
How common is infection by Listeria monocytogenes in healthy individuals?
Rare
How is infection by Listeria monocytogenes treated?
Penicillin or ampicillin (+ gentamicin).
Alternative: Trimethoprim-sulfamethoxazole
How is Listeria monocytogenes infection diagnosed?
Culture the organism from blood (blood agar), cerebrospinal fluid, or stool (although the latter is difficult and of limited value).
Blood agar in 5-10% CO2 at 35OC-37OC for 16-48h
Listeria selective agar (aesculin containing) in O2 at 35°C-37°C for 40-48h
What criteria is required for confirmation of Lab diagnosis of Listeria monocytogenes?
Gram stain Catalase +ve Tumbling motility Commercial ID Kit Ref lab
