Effects of Oleuropein and Peracetic Acid as Sanitizing Agents for Inactivation of Listeria monocytogenes Biofilms

摘要

The development of more efficient sanitizers for reducing the biofilm produced by pathogenic bacteria is of great importance, especially in the food industry. The aim of this study was to conduct a preliminary evaluation of the efficiency of oleuropein (OLE), extracted from olive leaves, and peracetic acid (PAA), alone or in combination, to inactivate biofilms formed by a strong biofilm-producer strain of Listeria monocytogenes (ATCC 7644). A disk diffusion method was also used to assess the susceptibility of the ATCC 7644 strain cells to OLE and/or PAA. Triplicate biofilm assays were prepared on stainless steel coupons (1x1 cm2) during 48 h without stirring. After incubation, the stainless steel was washed (NaCl 0.85%) and immersed in solutions of OLE (5.0 mg/mL) and/or PAA (2.0%) for 1 min. After 1-min treatment, the disinfectant solutions were removed from the tube. Two mL of sodium thiosulfate 0.1 M was placed in the tube to stop reaction. The inactivation of biofilms was assessed by confocal laser scanning microscopy. L. monocytogenes cells tested in the disk diffusion method was not susceptible to OLE (inhibition zone (IZ) = 6 mm), although its susceptibility was intermediate for PAA (IZ = 8.67 mm) and higher for PAA+OLE (IZ = 14 mm). Compared with PAA, OLE alone in contact with biofilms had also lower bactericidal activity on the biofilms. However, the treatment of OLE in combination with PAA resulted in greater inactivation of L. monocytogenes cells in biofilms. Results indicate a potential application of OLE for enhancing the bactericidal effect of PAA against L. monocytogenes biofilms, although further studies are necessary to understand the mechanisms of action of OLE in combination with commercial chemical sanitizers.