Recycling of waste: effect of polyphenols extract from olive oil water waste on Listeria monocytogenes and possible use as natural preservative in food

The food-borne pathogen Listeria monocytogenes (LM) is the causative agent of the severe human listeriosis. In the recent years, particular attention has been paid to the control of LM in ready-to-eat products. The persistence of this bacterium in food processing environments is mainly attributed to its ability to form biofilm. A phenols extract from olive vegetation water (PEOVW) is proposed as possible ingredient in food manufacture. This phenolic extract exhibits clear antimicrobial properties against several bacterial species. Microbiological and gene expression studies demonstrated an effect on biofilm and motility in Escherichia coli K-12. In this study the antimicrobial effects of the PEOVW were assessed against LM strains. 67 Listeria isolates (from meat, fish and dairy products) were genotyped by multilocus sequence typing (MLST, http://www.pasteur.fr/recherche/genopole/PF8/mlst/Lmono.html). Based on genotyping data, 26 LM strains were chosen to be characterized by antimicrobial susceptibility tests against PEOVW for a range of concentrations from 6 mg/ml to 0.375 mg/ml. Three groups of strains were identified based on their sensitivity and two strains resulted very sensitive as their minimum inhibitory concentration (MIC) was detected at 0.375 mg/ml. The sub-MIC effect of PEOVW on the expression of genes critical for biofilm synthesis and virulence was determined by real-time quantitative PCR (agrA, agrB, cyoA, degU, dnaK, fliG, flaA, inlA, mogR, prfA, trg, uvrA, yqdH). In addition, the PEOVW effects on LM strains were evaluated in a food model. A challenge test with LM on sausages enriched with PEOVW was carried out demonstrating a clear effect of PEOVW on LM growth. In general, LM was identified as a particularly susceptible microorganism to PEOVW and the gene expression analysis allowed to investigate the effects of PEOVW at molecular level.