Listeria species

From WikiVet English
Jump to navigation Jump to search
BACK TO INFECTIOUS AGENTS AND PARASITES
BACK TO BACTERIA

Overview

  • 6 species
  • Saprophytes in soil
  • L. monocytogenes and L. ivanovii are pathogens
  • Carried by sheep and goats and shed in faeces and milk especially during stress
  • Can cause septicaemia, encephalitis and abortion
  • Outbreaks of listeriosis often linked to silage feeding


Characteristics

  • Small Gram negative rods
  • Catalase positive, oxidase negative
  • Motile
  • Facultative anaerobes
  • L. monocytogenes is haemolytic on blood agar due to a cytolytic protein, listeriolysin; grows at range of pH values and temperatures
  • L. ivanovii produces strong haemolytic zone
  • Small, smooth, transparent colonies after 24 hours incubation
  • Grow on non-enriched media


Pathogenesis and pathogenicity

  • Infection by ingestion of contaminated feed
  • Bacteria penetrate M cells in intestinal Peyer's patches
  • Spread to tissues via blood and lymph
  • Transplacental transmission in pregnant animals
  • Bacteria may gain entry via breaks in oral or nasal mucosa, migrate in cranial nerves to cause neural signs
  • Causes formation of microabscesses and perivascular lymphocytic cuffs in brainstem
  • L. monocytogenes can replicate within phagocytic and non-phagocytic cell, and pass between cells without being exposed to the immune system
  • Surface proteins known as internalins allow adherence and uptake of the bacteria into cells
  • Listeriolysin produced by virulent strains destroys membranes of phagocytic vacuoles, releasing the bacteria into the cytoplasm
  • Listeria are motile in the cytoplasm
  • Bacteria induce formation of pseudopod projections in the cytoplasmic membrane, which are taken up with the bacteria into adjacent cells


Clinical infections