Listeria in macrophaag

L. monocytogenes found in this aneurysm,
see Gram stain (above)

Listeria monocytogenes

  • General information

    • the following information is not yet verified
      Is the bacterium that causes the infection listeriosis

      It can grow and reproduce in the host’s cells and is one of the most virulent food-borne pathogens.

      Family: Listeriaceae

      Of the seven species within the genus Listeria, only L. monocytogenes and L. ivanovii are pathogenic.

      Natural habitats
      They are widely distributed in the environment
      They have been isolated from soil, decaying vegetables, sewage, water, animal feed, fresh and frozen poultry, raw milk, cheese and slaughter house waste.

      Because of its widespread occurrence, L. monocytogenes has many opportunities to enter food productions and processing environments and, because of its ability to grow at 4oC, to cause human disease in persons ingesting colonized food.

      Clinical significance
      They cause the disease listeriosis, a serious infection caused by eating food contaminated with the bacteria.

      The disease affects primarily pregnant women, the bacteria is able to cross the placenta, and infect the fetus, which may result in spontaneous abortion or stillbirth, newborns, and adults with weakened immune systems

      Listeriosis is a serious disease for humans.
      The two main clinical manifestations are sepsis and meningitis.

      Meningitis is often complicated by encephalitis, a pathology that is unusual for bacterial infections

  • Diseases

  • Gram stain

    • the following information is not yet verified
      Regular, short gram positive rods,

      0.4-0.5 x 0.5-2.0 µm,

      that occur singly or in short chains, they can also reproduce in the cell (intracellular)

      Filaments of 6-20 µm, may occur in older or rough cultures.

      L. monocytogenes may be confused with members of the coryneform rods (especially in direct slides from blood cultures), since the cells may be arranged in V forms or palisades.

  • Culture characteristics

    • the following information is not yet verified

      Facultative anaerobic

      5% CO2 stimulates growth

      BA: colonies are small, smooth, white-grey and produce a narrow zone of hemolysis that frequently do not extend much beyond the edges of the colonies, whereas L.ivanovii exhibits a wide zone of hemolysis.

      McConkey: growth

      BBAØ: growth

      28oC ►motile 1-5 peritrichous flagella
      37oC ►less to no motility

      liquid medium ►"tumbling motility" when viewed with light microscopy
      solid medium ► "umbrella" growth

      Although L. monocytogenes is actively motile by means of peritrichous flagella at room temperature (20−25 °C), the organism does not synthesize flagella at body temperatures (37 °C)


      L. monocytogenes is enhanced in the vicinity of the S.aureus streak = CAMP-test positive

      L. ivanovii is CAMP-test negative (S.aureus streak)

      L. monocytogenes is CAMP-test negative (R.equi streak)

      L. ivanovii is enhanced in the vicinity of the R.equi streak = CAMP-test positive (a shovel shape)

  • Characteristics

  • References

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