Industry Information Session: Implementation of the 2011 Health Canada "Policy on Listeria monocytogenes in Ready-to-Eat Foods"
Topic 2: Characteristics of Listeria monocytogenes


Genus Listeria (family Listeriaceae)

6 most common species:

  • Listeria monocytogenes
  • Listeria ivanovii
  • Listeria innocua
  • Listeria grayi
  • Listeria welshimeri
  • Listeria seeligeri

When the term Listeria spp. is used, it refers to any and/or all of the Listeria species including Lm.

Listeria monocytogenes

(Section 4 of the Listeria Policy)

General Characteristics:

  • Size (1 – 2 µm x 0.5 µm)
  • Gram-positive bacterium, rod-shaped, non-spore forming
  • Can grow at wide pH range (4.4 or greater), water activity (aw) ≥ 0.92
  • Facultative anaerobe
  • Measured in colony-forming units (CFU) per gram (g) or per millilitre (ml)

Unique Characteristics:

  • Widely present in the natural and processing environments (e.g., soil, water, drains, ventilation)
  • Grows in food stored under refrigerated temperatures (-0.4 and 45 °C)
  • Pathogenic to humans (causes foodborne illness - listeriosis)

What is Listeriosis?

(Section 4 and 5 of the Listeria Policy)

  • A rare and serious disease
  • Symptoms may include vomiting, nausea, diarrhea, severe headache, constipation and persistent fever
  • Serious infections of Lm may cause miscarriages or stillbirths in pregnant women and lead to meningitis, septicaemia and death in high risk populations (e.g., the elderly or immunocompromised)

Risk Factors for Foodborn Listeriosis

(Section 4 and 5 of the Listeria Policy)

  • Presence of Lm in the food
  • Potential for growth of Lm in the food
  • Storage temperature and duration
  • Amount and frequency of consumption of a food contaminated with Lm
  • Host susceptibility (e.g., high-risk populations)
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