Listeria Monocytogenes

Listeria  Seven species  Listeria monocytogenes only human pathogen  L. ivanovii is primarily an animal pathogen  Gram positive, facultatively anaerobic bacillus  Short bacilli appear singly, in pairs, or in short chain  Can be mistaken for Streptococcus pneumoniae or Enterococcus   Neonates, elderly, pregnant women Patients with defective cell-mediated immunity Listeria  Growth at :(1° C to 45° C), high concentration of salt  Are motile at room temperature but not at 37°C  exhibit a characteristic end-over-end tumbling motion  Exhibits weak beta hemolysis when grown on sheep blood agar plates  Serotyping   13 serotypes: l/2a, 1/2b, and 4b (common) 4b: an epidemic of listeriosis cheese ( inadequately pasteurized milk) Pathogenesis and Immunity Facultative  intracellular pathogen Can grow in macrophages, epithelial cells, and cultured fibroblasts Infection is initiated in enterocytes  Several adhesin proteins  Entry into nonphagocytic cells by intenalins (e.g., InlA, InlB, InlC)   Acid  activates listeriolysin O, and 2 phospholipase C (release) Movement by protein ActA Pathogenesis and Immunity Internalins- interaction with host cell Listeriolysin Orelease the bacteria to cytosol ActA – penetrate to adjacent cell Pathogenesis and Immunity  Mortality rate of symptomatic listeria infections (20% to 30%)  is higher than that of almost all other foodborne diseases.  Iron is an important virulence factor.  Listeriae produce siderophores and are able to obtain iron from transferrin Epidemiology  Isolated in soil, water, and vegetation  Disease associated with consumption of contaminated Food products (e.g., soft cheese, milk, turkey, raw vegetables) Transplancental spread from mother to neonate  patients with defects in cellular immunity are particularly susceptible to severe infections.  Asymptomatic Fecal carriage: carriage (1% to 5%) of healthy people Epidemiology  Large outbreaks associated with  contaminated food products  30 million pounds of contaminated meat were recalled in one outbreak in 1999,  16 million pounds of processed turkey and chicken meat were recalled in a second multistate outbreak in 2000. Clinical Diseases 1- Neonatal Disease I) Early-onset disease (Granulomatosis infantiseptica) Acquired transplacentally in utero II) Late-onset disease Acquired at or soon after birth Occurs 2 to 3 weeks after birth Clinical Diseases 1- Neonatal Disease I) Early-onset disease (Granulomatosis infantiseptica) Can result in abortion, stillbirth, or premature birth Has a high mortality rate unless treated promptly Disseminated abscesses and granulomas in multiple organs neonatal sepsis, pustular lesions and granulomas containing Listeria monocytogenes in multiple organs 33 Clinical Diseases 1- Neonatal Disease II) Late-onset disease Meningitis or meningoencephalitis with septicemia Clinical signs and symptoms are not unique Like Group B streptococcal disease Often caused by serotype Ivb with high mortality Clinical Diseases 2- Disease in Healthy Adults asymptomatic In healthy adults mild influenza-like illness with or without gastroenteritis Meningitis: Most common form of Listeria infection in adults • Specially in Organ transplants or cancer and in pregnant women • High mortality (20% to 50%) and significant neurologic sequelae among survivors Primary Bacteremia: Commonly observed in pregnant women High-grade fever and hypotension Laboratory Diagnosis Microscopic morphology Gram-stain preparations of cerebrospinal fluid (CSF) or Blood Typically show no organisms (104 bacteria per mL CSF or less) If Gram stain shows organisms They are intracellular and extracellular gram-positive coccobacilli Microscopic Gram stain of Listeria monocytogenes in blood 36 Laboratory Diagnosis Culture Grows on most conventional laboratory media Small, round colonies Cold enrichment Beta hemolysis on sheep blood agar (weak and may not be observed initially) Motile at 25o C; "umbrella" type 37 Treatment, Prevention, and Control  Combination of gentamicin with either penicillin or ampicillin Listeria  are naturally resistant to cephalosporins Because listeriae are ubiquitous and most infections are sporadic, prevention and control are difficult  A vaccine is not available 38