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The aim of this study was to establish which of seven factors influence the adhesion strength and hence bacterial transfer between biofilms containing Listeria monocytogenes (pure and two-species biofilms) and tryptone soya agar (TSA) as a solid organic surface. The two-species biofilms were made of L. monocytogenes and one of the following species of bacteria: the nonpathogenic organisms Kocuria varians, Pseudomonas fluorescens, and Staphylococcus sciuri and CCL 63, an unidentified gram-negative bacterium isolated from the processing plant environment. We used biofilms prepared under conditions simulating open surfaces in meat-processing sites. The biofilm's adhesion strength and population were evaluated by making 12 contacts on a given whole biofilm (4.5 cm 2 ), using a new slice of a sterilized TSA cylinder for each contact, and plotting the logarithm CFU · cm ؊2 detached by each contact against the contact number. Three types of detachment kinetics were observed: biphasic kinetics, where the first slope may be either positive or negative, and monophasic kinetics. The bacteria that resisted a chlorinated alkaline product and a glutaraldehyde-and quaternary ammonium-based disinfectant had greater adhesion strengths than those determined for untreated biofilms. One of the four non-Listeria strains studied, Kocuria varians CCL 56, favored both the attachment and detachment of L. monocytogenes. The stainless steel had smaller bacterial populations than polymer materials, and non-Listeria bacteria adhered to it less strongly. Our results helped to evaluate measures aimed at controlling the immediate risk, linked to the presence of a large number of CFU in a foodstuff, and the delayed risk, linked to the persistence of L. monocytogenes and the occurrence of slightly contaminated foods that may become dangerous if L. monocytogenes multiplies during storage. Cleaning and disinfection reduce the immediate risk, while reducing the delayed risk should be achieved by lowering the adhesion strength, which the sanitizers used here cannot do at low concentrations.Microorganisms in foods may be derived from the raw materials, ingredients, personnel, or the work environment. Epidemics of listeriosis, which is rare but serious when it affects the so-called at-risk population (43), have been traced back to environmental contamination of food processing areas (48). Listeria monocytogenes genotypes, absent from the raw materials, may be repeatedly found in the finished products and on work surfaces (3). It is therefore interesting to identify the factors that affect adhesion strength and hence transfer of L. monocytogenes from an inert surface to a food following contact. Such data can be useful for quantitative analysis of the risks associated with ready-to-eat foods that may be contaminated during manufacture (11,18). Most studies of detachment of microbial cells use biofilms formed under dynamic conditions in which detachment is induced by liquid flow. These studies have shown the influence of numerous factors on the detachme...

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