Slicers, conveyor belts, bread feeding machines and water hoses are the areas most at risk for contamination by Listeria monocytogenes. This was the result of a study from the Institute of Food Safety and Hygiene in Zurich. It has been carried out on a sandwich plant over 12 months with the aim of evaluating the potential persistence of L. monocytogenes. The researchers comprised about 80 samples per visit, visiting the plant twice a week. All in all they took 1.192 samples from the equipment of the sandwich processing lines, 307 samples from the environment, 217 samples from ready-to-eat ingredients such as salmon, ham or salami and 529 samples from the environment and equipment after cleaning and disinfection. About 77.9 per cent L. monocytogenes strains were found on the equipment, in particular on slicers and conveyor belts. Strains of this Listeria genotype persisted for more than nine months in the processing environment, said the research team. After repeated cleaning (with revision of the cleaning and disinfection scheme), the bacteria were no longer found on slicers. Listeria monocytogenes is a food-born pathogen which causes bad infections called listeriosis. The study by S. Blatter, N. Giezendanner, R. Stephan and C. Zweifel will be published in Food Control.