Detection and typing of Lactococcus garvieae, Enterococcus spp. and Staphylococcus xylosus characterizing natural fermentations of Italian dairy products and sausages

The studyarises from a close collaboration among researchers who have the same aim of understanding the role of autochthonous microbial populations responsible for the typical properties of several traditional cheeses (Toma piemontese DOP, Robiola, Caprino Lombardo) and natural fermented sausages (salami friulani). Following the dynamic changes in the bacterial population during production, it was determined which are the species more represented and those more correlated with the typically of these products. Based on the results obtained, we focused our attention on Lactococcus garvieae, Enterococcus faecium, E. italicus (a new enterococcal species)and Staphylococcus xylosus strains. The isolates were characterized by using tests with high discriminatory power, such as analysis of the polymorphism of ribosomal DNA internal transcribed spacers, restriction analysis and partial sequencing of housekeeping genes, AFLP, Sau-PCR and RAPD analysis. Moreover, investigation on the phenotypic and biotechnological properties of the isolates affecting the flavor and structure of foods, such as the acidification rate, proteolysis and lipolysis, were carried out. We also evaluated the presence of some phenotypic characteristics correlated to the expression of virulence factors, such as antibiotic resistance, production of biogenic amines, gelatinase and haemolytic activity. Lastly, experiments with the aim to detect the presence of specific genetic determinants encoding these virulence factors, through specific amplification tests and/or Southern hybridization were performed as well.