Listeria identification • Gram stain • Beta-haemolysis • CAMP test • Tumbling motility • Esculin hydrolysis • Catalase positive, oxidase negative • API coryne • MALDITOF!
Other facts Listeria monocytogenes • Psychrophile • Easily destroyed by cooking, • Colonises 5-10% of population. • Found in environment (soil and water), animal faeces, raw foods. • Incubation period is 1-90 days (average 30 days) • Risk groups are pregnant women, neonates, elderly and immunocompromised.
Listeria monocytogenes Pathogenesis • Intra-cellular pathogen • Listeria bacteria have a surface protein “Internalin” • Attach to cells via “E-Cadherin” receptor on epithelial cells. • E-Cadherin receptors specifically present on epithelial cells in intestine, placenta and blood brain barrier.
Listeria in Pregnancy • Often flu like illness in mother • In early pregnancy, foetal infection may result in miscarriage • Maternal listeriosis in the second or third trimester results in a mortality of 40-50 % for the fetus4 • In later pregnancy foetal septicaemia may result in damage to multiple organs and stillbirth or neonatal death3 • The mortality rate varies from 3 – 50 % in live-born neonates infected with listeria5 • Perinatal listeria within 7 days of birth is often associated with prematurity and fulminant disease. Late onset disease (7 days to six weeks) often presents with meningitis. • Diagnosis with blood cultures.
CNS Listeria infections • In top 4 or 5 most common causes of bacterial meningitis. • Usually in neonates or elderly. Is 61 elderly? • CSF gram positive in 40% • CSF glucose not always low. • Blood cultures positive 75% • Mental fluctuation is more common for listeria meningitis than other bacterial causes of meningitis. • Listeria rhombo-encephalitis is a feared complication of CNS listeria infection with high mortality.
Listeria typing • Serotyping 1/2 and 4 only ones that cause problems in humans • PFGE: At least 71 different PFGE sub-types • Asc1 and Apa1 enzymes used.
Thoroughly cook raw food from animal sources. Wash raw vegetables thoroughly before eating. Separate uncooked meats from vegetables, cooked foods and ready-to-eat foods. Avoid unpasteurized milk or food. Wash hands, knives, and cutting boards with hot soapy water for at least 20 sec after handling uncooked foods. Observe all expiration dates on food items. Consume perishable and ready-to-eat foods as soon as possible. Do not eat soft cheeses: feta, brier, camembert, blue-veined, or Mexican-style etc. Do not eat refrigerated meat spreads, smoked salmon, smoked seafood; canned or shelf-stable smoked seafood may be eaten. Listeria monocytogenes is killed by cooking or by heating methods, including pasteurization. Prevention