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Listeria monocytogenes is a food-borne pathogen capable of adhering to a range of surfaces utilized within the food industry, including stainless steel. The factors required for the attachment of this ubiquitous organism to abiotic surfaces are still relatively unknown. In silico analysis of the L. monocytogenes EGD genome identified a putative cell wall-anchored protein (Lmo0435 [BapL]), which had similarity to proteins involved in biofilm formation by staphylococci. An insertion mutation was constructed in L. monocytogenes to determine the influence of this protein on attachment to abiotic surfaces. The results show that the protein may contribute to the surface adherence of strains that possess BapL, but it is not an essential requirement for all L. monocytogenes strains. Several BapL-negative field isolates demonstrated an ability to adhere to abiotic surfaces equivalent to that of BapL-positive strains. BapL is not required for the virulence of L. monocytogenes in mice.Listeria monocytogenes is a food-borne pathogen that causes serious illness, including meningitis, septicemia, and stillbirth, with a mortality rate of up to 30% (37). More recently, there have been reports of listerial gastroenteritis following the consumption of several different food types (16,34). A number of studies have demonstrated that this organism is able to persist in the food-processing environment for several months and even up to 10 years (23, 29). One of the major causes for concern about L. monocytogenes in these environments is its ability to attach to many different surfaces (2). Indeed, there is recent evidence to show that listerial biofilms formed inside the lumens of stainless steel tubes are able to withstand the shears generated by high-Reynolds-number flows (31). Biofilms, including those produced by L. monocytogenes, are more resistant to detergents and disinfectants (33) and also are a potential source of contamination within food-processing plants; hence, they pose a risk to the maintenance of product safety (27). Consequently, there is considerable interest in determining the mechanisms of attachment and biofilm formation.Our in silico analysis of the genome sequence of L. monocytogenes identified an open reading frame (lmo0435) for a protein with similarity to biofilm-associated proteins (Bap) believed to be important for the binding of staphylococci to abiotic surfaces (10). This Bap protein also has been implicated in the virulence of Staphylococcus aureus (10, 11). Thus, the aim of the current study was to establish if this protein (Lmo0435 [BapL]) of L. monocytogenes influenced biofilm formation and virulence and to determine the prevalence of the lmo0435 (bapL) gene within a selection of field isolates. MATERIALS AND METHODS Bacterial strains and plasmids.A list of the L. monocytogenes isolates and plasmids used in this study is given in Table 1. The strains were cultured in tryptone soya broth (TSB; Oxoid) or brain heart infusion agar (Oxoid) with shaking at 37°C unless otherwise stated. Escherichia coli JM...

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