Aims: The control of Listeria monocytogenes biofilm formation using lactocin AL705 bacteriocin at sub-minimum inhibitory concentrations (MICs) through an antiquorum sensing strategy, was preliminarily investigated. Methods and Results: The screening for biofilm formation of different Listeria species at 10°C allowed selecting L. monocytogenes FBUNT for its use as biofilm producer. MIC and minimum bactericidal concentration of lactocin AL705 purified extract against the pathogen was determined. Bacteriocin sub-MICs were used to evaluate biofilm reduction. Concentrations between 2Á5-20 AU ml À1 of lactocin AL705 produced significant decreases in biofilm formation without affecting the growth of the pathogen after 3 days of incubation. When bacteriocin concentrations (5-20 arbitrary units per millilitre (AU ml À1 )) were investigated as quorum sensing (QS) inhibitors using Vibrio harveyi as reporter strain, a significant reduction in luminescence by lactocin AL705 (20 AU ml À1 ) was observed. Even when L. monocytogenes produced AI-2 like molecules as recognized by the reporter strain, bacteriocins did not interfere with this compound. Conclusion: Antilisterial lactocin AL705 used to disrupt QS through a signal molecule inactivation was able to control L. monocytogenes FBUNT biofilm formation. Other molecule(s) different from the AI-2 involved during biofilm formation could be acting as target of the bacteriocin. Significance and Impact of the Study: The use of bacteriocins derived from food-grade micro-organisms as a QS inhibition represents an effective strategy to control pathogens as well as an environmentally friendly sanitation method to mitigate postprocessing food contamination.Journal of Applied Microbiology 127, 911--920

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Listeria monocytogenes is one of the major food-related pathogens and is able to survive and multiply under different stress conditions. Its persistence in industrial premises and foods is partially due to its ability to form biofilm. Thus, as a natural strategy to overcome L. monocytogenes biofilm formation, the treatment with lactocin AL705 using a sublethal dose (20AU/ml) was explored. The effect of the presence of the bacteriocin on the biofilm formation at 10°C of L. monocytogenes FBUNT was evaluated for its proteome and compared to the proteomes of planktonic and sessile cells grown at 10°C in the absence of lactocin. Compared to planktonic cells, adaptation of sessile cells during cold stress involved protein abundance shifts associated with ribosomes function and biogenesis, cell membrane functionality, carbohydrate and amino acid metabolism, and transport. When sessile cells were treated with lactocin AL705, proteins’ up-regulation were mostly related to carbohydrate metabolism and nutrient transport in an attempt to compensate for impaired energy generation caused by bacteriocin interacting with the cytoplasmic membrane. Notably, transport systems such as β-glucosidase IIABC (lmo0027), cellobiose (lmo2763), and trehalose (lmo1255) specific PTS proteins were highly overexpressed. In addition, mannose (lmo0098), a specific PTS protein indicating the adaptive response of sessile cells to the bacteriocin, was downregulated as this PTS system acts as a class IIa bacteriocin receptor. A sublethal dose of lactocin AL705 was able to reduce the biofilm formation in L. monocytogenes FBUNT and this bacteriocin induced adaptation mechanisms in treated sessile cells. These results constitute valuable data related to specific proteins targeting the control of L. monocytogenes biofilm upon bacteriocin treatment.

Life expectancy has dramatically increased over the past 200 years, but modern life factors such as environmental exposure, antibiotic overuse, C-section deliveries, limited breast-feeding, and diets poor in fibers and microbes could be associated with the rise of noncommunicable diseases such as overweight, obesity, diabetes, food allergies, and colorectal cancer as well as other conditions such as mental disorders. Microbial interventions that range from transplanting a whole undefined microbial community from a healthy gut to an ill one, e.g., so-called fecal microbiota transplantation or vaginal seeding, to the administration of selected well-characterized microbes, either live (probiotics) or not (postbiotics), with efficacy demonstrated in clinical trials, may be effective tools to treat or prevent acute and chronic diseases that humans still face, enhancing the quality of life.