Lactobacillus sakei 1 and its bacteriocin influence adhesion of Listeria monocytogenes on stainless steel surface

Listeria monocytogenes is of particular concern for the food industry due to its psychrotolerant and ubiquitous nature. In this work, the ability of L. monocytogenes culturable cells to adhere to stainless steel coupons was studied in co-culture with the bacteriocin-producing food isolate Lactobacillus sakei 1 as well as in the presence of the cell-free neutralized supernatant of L. sakei 1 (CFSN-S1) containing sakacin 1. Results were compared with counts obtained using a non bacteriocin-producing strain (L. sakei ATCC 15521) and its bacteriocin free supernatant (CFSN-SA). Culturable adherent L. monocytogenes and lactobacilli cells were enumerated respectively on PALCAM and MRS agars at 3-h intervals for up to 12 h and after 24 and 48 h of incubation. Bacteriocin activity was evaluated by critical dilution method. After 6 h of incubation, the number of adhered L. monocytogenes cells in pure culture increased from 3.8 to 5.3 log CFU/cm2 (48h). Co-culture with L. sakei 1 decreased the number of adhered L. monocytogenes cells (P < 0.001) during all sampling times with counts lower than 3.0 log CFU/cm2. The CFNS-S1 also led to a significant and similar reduction in culturable adhered L. monocytogenes counts for up to 24 h of incubation, however after 48 h of incubation, re-growth of L. monocytogenes number of adhered cells was observed, likely due to lack of competition for nutrients. L. sakei ATCC 15521 or its supernatant (CFNS-SA) did not reduce the number of adhered L. monocytogenes cells on stainless steel surface and from 6 h of incubation, listerial counts were between 4.3 and 4.5 log CFU/cm2. These results indicate that L. sakei 1 and its bacteriocin sakacin 1 may be useful to inhibit early stages of L. monocytogenes adherence to abiotic surface.