Recently, the surface of the wings of the Psaltoda claripennis cicada species has been shown to possess bactericidal properties and it has been suggested that the nanostructure present on the wings was responsible for the bacterial death. We have studied the surface-

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Listeria monocytogenes is a food pathogen that can attach on most of the surfaces encountered in the food industry. Biofilms are three-dimensional microbial structures that facilitate the persistence of pathogens on surfaces, their resistance toward antimicrobials, and the final contamination of processed goods. So far, little is known about the structural dynamics of L. monocytogenes biofilm formation and its regulation. The aims of this study were, by combining genetics and time-lapse laser-scanning confocal microscopy (LSCM), (i) to characterize the structural dynamics of L. monocytogenes EGD-e sessile growth in two nutritional environments (with or without a nutrient flow), and (ii) to evaluate the possible role of the L. monocytogenes agr system during biofilm formation by tracking the spatiotemporal fluorescence expression of a green fluorescent protein (GFP) reporter system. In the absence of nutrient flow (static conditions), unstructured biofilms composed of a few layers of cells that covered the substratum were observed. In contrast, when grown under dynamic conditions, L. monocytogenes EGD-e biofilms were highly organized. Indeed, ball-shaped microcolonies were surrounded by a network of knitted chains. The spatiotemporal tracking of fluorescence emitted by the GFP reporter system revealed that agr expression was barely detectable under static conditions, but it progressively increased during 40 h under dynamic conditions. Moreover, spatial analysis revealed that agr was expressed preferentially in cells located outside the microcolonies. Finally, the in-frame deletion of agrA, which encodes a transcriptional regulator, resulted in a decrease in initial adherence without affecting the subsequent biofilm development.Biofilms are communities of microorganisms attached to a surface (44). Several steps can be identified during biofilm development. After an initial step of reversible, then irreversible, adherence, bacteria grow as microcolonies and spread on the surface; also, biofilms develop as complex, three-dimensional (3D) structures during the maturation step (17). The microorganisms undergo profound changes during their transition from planktonic cells (free-floating organisms) to cells that are part of a complex, surface-attached community (sessile organisms) (44), and cells develop an increased resistance to antimicrobial agents (34,38,64). For this reason, the removal of established biofilms requires harsh treatments, with most using oxidizing biocides (18,20,25,54). The presence of biofilms raises safety issues in the food industry, especially when biofilms are located on food-processing surfaces and pipelines that are unreachable by washing agents (8). Clearly, biofilms can become a health hazard by harboring pathogenic bacteria such as Listeria monocytogenes (4). Moreover, L. monocytogenes is capable of attaching and developing biofilms on a variety of surfaces, such as stainless steel, polymers, and rubber gaskets (2,3,13,36,40). L. monocytogenes is a gram-positive human pathogen that is resp...