Listeria monocytogenes is a pathogenic bacterium that may survive the harsh conditions of the human gastrointestinal tract and it is the etiological agent of listeriosis, a rare opportunistic disease with high fatality rate, acquired mainly by ingestion of contaminated food. Due to the severity of disease and large economic impact, there is great deal of attention for developing preventive measures to control the spread of L. monocytogenes.
In this study, adhesion and invasion assays were conducted with L. monocytogenes in a model of intestinal epithelial cells (Caco-2 line) in co-culture with Leuconostoc mesenteroides A11, a food isolate lactic acid bacterium (LAB) producer of peptides with antilisterial activity (bacteriocin), previously characterized (De Martinis et al., 2001; Martinez & De Martinis, 2006). Before L. mesenteroides A11 in adhesion/invasion assays, the spot on the lawn agar antagonism test was performed to check for bacteriocin production according to Martinez and De Martinis. L. mesenteroides A11 and L. monocytogenes were grown in MRS and BHI broths, respectively. MRS broth culture of L. mesenteroides A11 was used to prepare a cell-free supernatant (CFS) containing the bacteriocin produced. The concentrations tested for bacteriocin preparations in adhesion and invasion assays with L. monocytogenes to Caco-2 cells were 0%, 10%, 25%, 50%, 75% and 90% of CFS diluted in DMEM (vol/vol). The titre of bacteriocin in CFS was determined according to Mayr-Harting, Hedges and Berkeley.
In adhesion assays with CFS at 50%, there was a decrease of 54.1% in the number of L. monocytogenes adhered to Caco-2 cells, compared to the control group. Inhibitory activity was also observed in invasion assays of Caco-2 cells by L. monocytogenes in the presence of 50%, 75% and 90% of bacteriocin.
L. mesenteroides A11 protected eukaryotic cells against L. monocytogenes infection.