Comparazione delle analisi fenotipiche e proteomiche di ceppi di Enterococcus faecalis di origine alimentare e nosocomiale

The use of Enterococcus faecalis both in food and probiotic industry counteracts with its increasing importance as human pathogen; several molecules involved in virulence have been identified over the years, such as the secreted proteases GelE and SprE, an hemolysin and a manganese superoxide dismutase. These molecules were found to be produced mainly by hospital isolates, but also by some food strains. In this study, several phenotypic assays were performed in order to assess the ability of 14 E. faecalis strains with different origin - food, hospital and a probiotic preparation - to produce some known virulence factors. Their susceptibility to some antibiotics and their ability to form a biofilm were tested as well. Interestingly, one of the food isolates showed to be positive for most of the investigated virulence factors. Moreover, four proteomic profiles were obtained by growing the above-mentioned food strain and a clinical isolate both in a selective medium and in a medium simulating the colonic environment - SCEM - before performing an SDS-PAGE and a LC-MS/MS analysis on the proteins present in the cultures supernatants. The comparison of such proteomic profiles highlighted that 112 proteins were common to all the samples while 36 were detected only when bacteria were grown in SCEM. Most of them were ribosomal proteins, proteins known to be involved in stress response and enzymes connected to cell wall synthesis. Also, proteomics results showed that almost all the virulence factors already investigated during the phenotypic characterization are produced under both the investigated conditions. This is not the case for a manganese superoxide dismutase that was not detected in the samples prepared by growing the strains in SCEM; on the contrary, in such samples, a NADH peroxidase was present. Altogether, these results confirm that the expression of virulence factors is merely strain-specific and not related to the strain origin; further investigations might explain how the colonic environment acts on proteins expression and regulation.