Food safety is a key priority in the food industry, ensuring that food is safe for human consumption and free of pathogens that can cause disease. However, cross-contamination remains one of the main threats to food safety, as it facilitates the spread of microorganisms between different foods, surfaces and work utensils. This contamination is particularly problematic when it involves pathogens such as Listeria monocytogenes and Salmonella enterica. Both microorganisms are capable of forming biofilms on food surfaces. These structures hinder the action of conventional disinfectants. The development of biofilms on food surfaces represents a challenge for the food industry. Traditional cleaning and disinfection methods are not always effective in completely eradicating them, making the prevention and control of these biofilms a crucial task. In response to this challenge, alternative strategies have begun to be developed that include the use of essential oils and biocontrol methods as emerging solutions to prevent and eliminate the formation of biofilms. Essential oils have been shown to possess natural antimicrobial properties that can be effective against a wide range of food pathogens. On the other hand, biocontrol through the introduction of non-pathogenic microorganisms that compete with pathogens for nutrients or space, or that produce specific antimicrobial compounds, is emerging as another innovative strategy. In order to develop new strategies for the control of biofilms of L. monocytogenes and S. enterica on food surfaces, the formation capacity, macromolecular composition and architecture of the biofilms of both species were first characterized. The results showed that both bacteria have a remarkable capacity to form biofilms on stainless steel surfaces. Regarding the composition of the biofilm matrix, a predominance of proteins was observed in both cases. 3D representations of the architecture of the biofilms revealed an irregular and disorganized distribution of the matrix components. Subsequently, based on the preliminary results described above, strategies were designed with the aim of preventing and eliminating these biofilms. As a first approach, the antimicrobial effectiveness of several essential oils was evaluated to select the most suitable for use in combination with enzymes. Among the oils evaluated, cassia essential oil proved to be the most effective against L. monocytogenes and S. enterica. In turn, it was determined that the application of subinhibitory doses of cassia essential oil reduced tolerance to the antimicrobial effect in several strains, with L. monocytogenes ST-388 and S. Typhimurium CECT 4594 showing the greatest reductions. Likewise, in general, a limited change was observed in the sensitivity profile of the strains evaluated to antibiotics after exposure to cassia essential oil. Based on these results, eight treatments combining different enzymes (protease, amylase and mannanase) with cassia essential oil were evaluated to determine the best strategy for removing mature biofilms. The combination of protease, amylase and cassia essential oil was selected as the most effective. Quantitative and qualitative results showed that this treatment achieved reductions in cell counts close to 100%, in addition to breaking up the biofilm architecture. Finally, as a second strategy, biocontrol was used. The capacity of Bacillus safensis to ecologically replace L. monocytogenes and S. enterica on stainless steel surfaces was evaluated. The presence of preformed biofilms of B. safensis significantly reduced the counts of both pathogens in bispecies biofilms, with L. monocytogenes being the most affected, which makes it a weak competitor against B. safensis.
Biofilms de listeria monocytogenes y salmonella enterica en instalaciones alimentarias : desarrollo de estrategias para el control de ambos patógenos
Cervantes Huaman, B. R. H. (Author). 5 Nov 2024
Student thesis: Doctoral thesis
Student thesis: Doctoral thesis