Bovis ISSN 2398-2993

Listeria monocytogenes

Contributor(s): Veronica Fowler , Tammy Hassel




  • Kingdom: bacteria.
  • Phylum: firmicutes.
  • Class: bacilli.
  • Order: bacillales.
  • Family: listeriaceae.
  • Genus: listeria.
  • Species: listeria monocytogenes.


  • Listeria: named after Joseph Lister, an English surgeon and pioneer of antisepsis.
  • Monocytogenes: monocyte-producing.

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Clinical Effects



  • Widespread distribution within the environment, eg in soil, silage, stream water or sewage.
  • Found in numerous animal species, but most commonly in ruminants.


  • Entry into the body through gastrointestinal tract.
  • L. monocytogenes is facultatively intracellular and grows and proliferates within macrophages (cells within the body which ingest and destroy most other invading bacteria).
  • L. monocytogenes is internalized by a macrophage within a structure called a phagosome and is able to avoid being digested by releasing toxins which lyse the phagosome.
  • Lysis of the macrophages causes spread of the pathogen to surrounding cells.
  • The bacteria can polymerise actin by means of the protein Act A, enhancing their intracellular mobility.


  • Poor quality silage, where fermentation does not produce acidic conditions which inhibit the bacteria, is cited as one of the most frequent sources of L. monocytogenes outbreaks.
  • Once infected, cattle shed the bacteria in faeces, milk and urine and the main route of transmission of infection of other cattle occurs by ingestion of contaminated food or water (faecal-oral route).
  • D-galactose residues on the surface of L. monocytogenes attach to D-galactose receptors on host cell walls, commonly M cells and Peyer's patches of the host's intestinal mucosa. L. monocytogenes then translocates past the intestinal membrane and into the body.
  • In septicemic/abortive listeriosis the primary route of entry is through the intestinal mucosa.
  • Listeric encephalitis occurs when L. monocytogenes breaches the oral mucosa through small wounds and ascends the trigeminal nerve causing a localized infection of the brain stem.

Pathological effects

  • Uterine infection Vaginal discharges.
  • Abortion Abortion & stillbirths.
  • Septicemia Septicemia.
  • Infertility.
  • Sudden death.
  • Encephalitis, characterized by the following:
    • Depression.
    • Ipsilateral weakness.
    • Trigeminal and facial nerve paralysis.
    • Circling.


Control via animal

  • Isolate affected animals.
  • Remove and replace sources which could potentially transmit the pathogen, if contaminated, eg food and water.

Control via chemotherapies

  • Listeriosis is treated with antibiotics such as Penicillins Penicillins and Tetracyclines Tetracyclines.
  • If encephalitis ensues, high doses of aggressive antibiotics are required and even then the treatment may not be enough to prevent death of the animal. (approx 50% of listeric encephalitis cases result in death).

Control via environment

  • The risk of listeriosis can be lowered by feeding good quality silage with a low pH.
  • Any leftover silage should be removed after feeding.


  • As L. monocytogenes is an intracellular parasite there is no effective vaccine to prevent infection.


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Further Reading


Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Nucera D M, Grassi M A, Morra P, Piano S, Tabacco E & Borreani G (2016) Detection, identification, and typing of Listeria species from baled silages fed to dairy cows. J Dairy Sci 99 (8), 6121-33 PubMed.
  • Gasanov U, Hughes D & Hansbro P M (2005) Methods for the isolation and identification
    of Listeria spp. and Listeria monocytogenes: a review.
    FEMS Microbiol Rev 29 (5), 851-75 PubMed.
  • Fensterbank R, Audurier A, Godu J, Guerrault P & Malo N (1984) Listeria strains
    isolated from sick animals and consumed silage.
    Ann Rech Vet 15 (1), 113-8 PubMed.

Other sources of information

  • Pimus Labs - Client Guidelines. Listeria Sampling - Swab Method. Website: Last accessed 18th February 2016.
  • VetBac - Listeria monocytogenes. Website: Last accessed 16th February 2016.