Influence of temperature and growth phase on expression of a 104-kilodalton Listeria adhesion protein in Listeria monocytogenes

Interaction of Listeria monocytogenes,vith mammalian intestinal cells is be lieved to be an important first step in Listeria pathogenesis. Transposon ( Tn916) mutagenesis provided strong evidence that a 104-kDa surface protein, designated the Listeria adhesion protein (LAP), nas involved in adherence of L. monocytogenes to a human enterocyte-like Caco-2 cell line (V. Pandiri pally, D. Westbrook, G. Sunki, and A. Bhunia, J. Med. Microbiol. 48:117-124 , 1999). In this study, expression of LAP in L. monocytogenes at various gr owth temperatures (25, 37, and 42 degrees C) and in various growth phases w as determined by performing an enzyme-linked immunoassay (ELISA) and Wester n blotting with a specific monoclonal antibody (monoclonal antibody H7). Th e ELISA and Western blot results indicated that there was a significant inc rease in LAP expression over time only at 37 and 42 degrees C and that the level of LAP expression was low during the exponential phase and high durin g the stationary phase. In contrast, there were not significant differences in LAP expression between the exponential and stationary phases at 25 degr ees C. Examination of the adhesion of L. monocytogenes cells from exponenti al-phase (12-h) or stationary-phase (24-h) cultures grown at 37 degrees C t o Caco-2 cells revealed that there were not significant differences in adhe sion. Although expression of L. monocytogenes LAP was different at differen t growth temperatures and in different growth phases, enhanced expression d id not result in increased adhesion, possibly because only a few LAP molecu les were sufficient to initiate binding to Caco-2 cells.