Listeria monocytogenes: Potential presence of (semi-)permanent local sources of bacterial variants in the Faroe Islands?

Listeria monocytogenes is a Gram-positive bacterium found in a variety of environments, ranging from soil and water through food production plants to livestock and humans (Fenlon 1999; Ivanek et al 2006). Its main natural habitat is soil and degrading plant materials, while in sea water the viability is lost within a period of days to weeks (Bremer et al 1998; CAC 2007), occasionally needing longer periods (Hsu et al 2005). L. monocytogenes is an acid-, salt-, cold tolerant and facultative aerobe. These properties make it able to survive and grow under many conditions used in food preservation, including the abilities to grow in fridge temperatures. As the bacterium is wide-spread, virtually no food source is safe from possible contamination (Madigan et al 2009A). In the modern society, humans mainly contacts Listeria through food. Most countries have low limits of the allowed amount of Listeria in food, but some countries have zero-tolerance, including Russia, which is an important market for Faroese fish. The pathogenicity in healthy adults is generally low, but it may be lethal in children, immunocompromized persons, etc. In pregnant women, L. monocytogenes may lead to abortion. Thus, listeriosis is a disease that can range from mild illness to fatal meningitis (Madigan et al 2009B). L. monocytogenes is a transitory resident in the intestinal tract in humans, with 2 to 10% of the general population being carriers, but without any apparent health consequences (Farber and Peterkin 1991). In this project, we have investigated the potential presence of L. monocytogenes around three aquaculture sites (i.e., different fjords) in the Faroe Islands and in a salmon processing plant receiving salmon from all three sites. The project had two main aims, to investigate the potential presence of Listeria in the sea water around the aquaculture sites and in the processing line, and to investigate potential genetic relatedness of the Listeria detected.