L. monocytogenes is a gram positive, non-spore forming rod that may be isolated from a variety of sources including soil, silage, sewage, food-processing environments, raw meats and the faeces of healthy humans and animals (FDA 2003). L. monocytogenes grows in the temperature range –0.4°C to 45°C, over a broad range of pH (4.6–9.2) and to an aw as low as 0.90 (glycerol as humectant) or 0.92 (NaCl as humectant) (ICMSF 1996). An important factor in terms of food-borne transmission is that the organism survives well under frozen conditions and has the ability to grow at low temperatures.
