Efecto de diferentes biocidas sobre la resistencia a los antibióticos, los biofilms y el proteoma en cepas de Listeria monocytogenes y Salmonella enterica de origen alimentario

Zusammenfassung

The prevalence of antibiotic resistance represents a growing challenge for public health worldwide, making it a priority to adopt the necessary measures for its control. Furthermore, most pathogenic bacteria are capable of forming biofilms, which substantially increases their resistance to antibiotics and biocides, while making the search for new, more effective antimicrobial compounds a necessity. The effect of different biocides on antibiotic resistance, biofilms and proteome in strains of Listeria monocytogenes and Salmonella enterica of food origin was studied, focusing on the problem of mixed biofilms, which are more common in nature in general and in the food industry in particular. The sessile cells of the biofilms formed by L. monocytogenes and S. enterica presented greater resistance to peracetic acid than the monospecies biofilms of these microorganisms. Individual constituents of biofilms exposed to different antimicrobial treatments were evaluated by confocal laser scanning microscopy (CLSM) using specific fluorescent dyes. A strong positive correlation (P < 0.01) was found between total biofilm biovolume and the biovolume of live cells, proteins and β- polysaccharides, which can serve as useful markers of the presence of biofilms. It was observed that the exposure of bacteria to subinhibitory concentrations of biocides causes the emergence of resistance to different antibiotics, a fact that emphasises the need to use adequate doses of disinfectants in food processing environments. Of the compounds evaluated, the one with the least capacity to cause resistance was peracetic acid. In the search for new antimicrobial agents, metallic nanoparticles stand out, especially copper ones, which are presented as an interesting alternative to eradicate biofilms. Furthermore, synergies were observed in the combination of silver nanoparticles with fosfomycin, with an increased antibacterial effect compared to their individual application. For their part, enzymatic treatments allowed the elimination of some key components of the extracellular polymeric matrix of the biofilms and facilitated the access of other antimicrobial compounds, detecting a decrease in the mass of viable cells, which was substantial in the case of pronase at 4,000 ppm and deoxyribonuclease at 2,000 ppm. Proteomics is an important tool that improves the understanding of the different strategies of bacteria to fight antibiotics and disinfectants. The proteomic analysis carried out facilitates the understanding of the proteins involved in bacterial pathogenesis, allowing us to expand knowledge about the mechanisms of virulence and antimicrobial resistance. These results can be a starting point in the search for new targets for the development of more effective drugs. Last, a review of 586 scientific articles was carried out with the aim of compiling the available literature on the prevalence of methicillin- resistant Staphylococcus aureus (MRSA) in different foods for human consumption,determining the most frequent types and collecting the methodology used in each case to know which one offers the best detection of positive samples. The great variability of methodologies used for the study of MRSA highlights the need to develop a harmonised protocol for the study of this microorganism in foods. The results of this doctoral thesis allowed us to acquire knowledge that can contribute to the improvement of food safety.