The challenge of enumerating Listeria monocytogenes in food

• We summed up the current knowledge concerning L. monocytogenes enumeration.
• Enumeration difficulties are linked to low contamination levels in foods.
• The improvement of L. monocytogenes enumeration gave place to a considerable amount of research projects.
• Both new culture based techniques and molecular methods are not largely used.
• None new method is ideal for any purpose, and users must choose them according to their needs.

Listeria monocytogenes is recognised as a serious foodborne pathogen in humans. However, food products are usually contaminated at low levels (i.e. <100 CFU/g) and there is still no adequate enumeration method for testing food. Much research has been carried out to improve Listeria enumeration methods, leading to several proposed alternative methods such as the most probable number technique, molecular-based methods and bacterial cell concentration techniques. Here, we catalogue the current knowledge concerning L. monocytogenes enumeration, with a particular focus on the problem of enumerating low level contamination.