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Listeria monocytogenes L.M.
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Listeria monocytogenes L.M.

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    1. Listeria monocytogenes (L.M.) Dr. Mohamed Al-Sweify

    2. Objectives: Nomenclature Morphology and physiology of LM Virulence and pathogenesis Epidemiology Clinical illness Lab diagnosis Treatment Prevention and control

    3. Named after the English surgeon: Lord Lister. monocytogenes: since its membrane extracts stimulate monocyte production in rabbits.

    4. L.M. morphology and physiology Short (0.5 1.5 m), non-branching, gram+ve facultative anaerobic rod Grows at a broad temperature range (1- 45C) Grows In a high concentration of salt. Motile; end-over-end tumbling motion. Exhibits weak -hemolysis on sheep blood agar Scope of hosts: neonates, the elderly, pregnant women, and patients with defective CM immunity.

    6. Virulence and Pathogenesis Intracellular pathogen which can grow in macrophages and epithelial cells. Infection is initiated in the enterocytes or M cells in Peyer's patches. Entry is mediated by 6 internalins which interact with gp receptors on the cell surface. The acid pH of the phagolysosome activates a bacterial exotoxin (listeriolysin O) and two different phospholipase C enzymes, leading to release of the bacteria into the cell cytosol.

    7. Inl A mediated entry of Listeria monocytogenes

    8. The bacteria replicate and move to the cell membrane, where a protrusion is formed, pushing the bacterium into the adjacent cell. After adjacent cell ingests the bacterium, the process of phagolysosomal lysis, bacterial replication, and directional movement repeats (see picture) Subsequent entry into macrophage carries bacteria to liver and spleen ? disseminated disease.

    11. Since it can replicate in MF and move within cells, LM can avoid ???? So, ????? immunity is relatively unimportant. Accordingly, patients with defects in ???? are particularly susceptible to severe infections. Virulence and Pathogenesiscont.

    12. Epidemiology L.M. is isolated from soil, and the faeces of mammals, birds, fish, insects, and other animals. Since the organism is ubiquitous ? exposure and transient colonization. Fecal carriage is estimated to occur in 1% to 5% of healthy people (?? restaurant cooks, food handlers).

    13. Epidemiology..continued.. Food poisoning events:??? ??? Many mild infections are not reported (2500/year) Large outbreaks associated with contaminated food products have been documented. listeriosis is associated with consumption of contaminated milk, soft cheese, undercooked meat (e.g., turkey franks, cold cuts, microwaved beef), unwashed raw vegetables, and cabbage. For example, 15X106 kg of contaminated meat were recalled in 1999 outbreak in US. Foods with small numbers of organisms can become grossly contaminated during prolonged refrigeration... Why ? Mortality rate of listeriosis (20% to 30%) is higher than that of almost all other foodborne diseases.

    15. Clinical Illnesses Neonatal disease Early onset disease: granulomatosis infantiseptica. Is acquired transplacentally. Is characterized by disseminated abscesses and granulomas in multiple organs ? ABORTION. Late-onset disease: at or soon after birth; as meningitis or meningoencephalitis with septicemia. Disease in healthy adults: typically an influenza-like illness with or without gastroenteritis, chills and fever due to bacteremia. Disease in CMI-deficient adults: a primary bacteremia or disseminated disease with high fever, hypotension and meningitis. Endocarditis may complicate LM bacteremia. Meningitis is the most common form of listeria infection in CMI-deficient adults

    16. A 39 weeks newborn (3400 g) suffering from granulomatosis infantiseptica due to LM trans-placental infection. Findings are: Hepatosplenomegaly, monocytosis, fever, cutaneous lesions and pulmonary thrombosis

    17. Laboratory Diagnosis Microscopy: Gram stain preparations of CSF typically show no organisms, because the bacteria are generally present in conc. below limit of detection (104 /ml CSF): If it showed; IC and EC gram+ve coccobacilli. Be careful to distinguish them from S. pneumoniae, Enterococcus, and Corynebacterium.

    18. Lab diagnosis..cont. 2. Culture and biochemical identification: Listeria grows on blood agar (1-2 days), selective chromogenic agar (new) and many other selective media.. Use selective media and cold enrichment (storage of the specimen in the refrigerator for a prolonged period) to detect listeriae in contaminated specimens. On Blood Agar: produces weak -Hemolysis can serve to distinguish Listeria from morphologically similar bacteria.

    19. LM on selective chromogenic medium, comprised of OCLA Base (ISO) and Listeria Selective Supplement (ISO) to detects the -glucosidase activity common to all Listeria species resulting in distinct blue colonies. The addition of phosphatidylinositol or phosphatidylecholine detects phosphatidylinositol phospholipase C (PIPLC) or phosphatidycholine phospholipase C (PCPLC). Both enzymes are produced by pathogenic Listeria species. Either supplementation results in a clearly visible, opaque white halo around pathogenic Listeria colonies.Listeria on agar plate.

    21. Hemolysis is enhanced when the organisms are grown next to -hemolytic Staphylococcus aureus . This enhanced hemolysis is referred to as a positive CAMP test (Christie, Atkins, Munch-Petersen). The characteristic motility of the organism in a liquid medium is also helpful for the preliminary identification of listeriae. Selected biochemical and serologic tests are used to identify the pathogen definitively. 3. Serotyping: A total of 13 serotypes have been described, with 1/2a, 1/2b, and 4b responsible for most infections in neonates and adults.

    22. Listeria in a CAMP test

    23. TREATMENT, PREVENTION, AND CONTROL Currently, penicillin or ampicillin, either alone or with gentamicin, is the treatment of choice for infections with L. monocytogenes. Listeriae shows intrinsic resistance to cephalosporins. Erythromycin can be used in patients allergic to penicillin. Co-trimoxazole and Tetracycline resistance is reported and increasing (conjugative plasmids and transposons that originated in enterococci). Because listeriae are ubiquitous and most infections are sporadic, prevention and control are difficult. No vaccine.

    24. Question of the day: Discuss how Listeria species could be used in anti-cancer therapy ?