Food-related staphylococcus aureus biofilms: characterization and control

Staphylococcus aureus is an ubiquitous and opportunistic pathogen. S. aureus is frequently involved in clinical infection, but it is also an important foodborne pathogen. In fact, some strains of S. aureus have enterotoxigenic capacity and can be potentially responsible for food intoxication (staphylococcal food poisoning). Furthermore, another challenge is represented by methicillin-resistant S. aureus (MRSA). Initially associated with nosocomial infections, it has been demonstrated that such β-lactams resistant bacteria can be present in retail foods, including pork, beef, and dairy products. The capability of microorganisms to produce biofilms – complex three-dimensional structures of cells embedded in self-produced exopolymeric substances, strictly adhered to a surface – is an important persistence and dissemination mechanism of some foodborne bacteria, including S. aureus. Different researchers studied the biofilm formation by members of Staphylococcus genus, but many of these investigations were focused on clinical aspects of this process. Furthermore, many studies that investigated the ability of dairy-related MRSA to form biofilm were focused on isolates collected from the herd, and not from the final products, which are more relevant in a food safety perspective. This thesis dealt with the molecular characterization of methicillin –sensitive and –resistant S. aureus (MSSA and MRSA) isolated from food, food environments, and food handlers, in relationship with their ability to produce biofilms on common food-contact surfaces. For the first time, the relationship between S. aureus genotypes (obtained by Ribosome-Spacer PCR) and biofilm formation was investigated. MSSA and MRSA isolates were tested for the capacity to produce biofilms on food contact surfaces, increasing the knowledge about the molecular mechanisms potentially involved in this process. The second part of the thesis (chapters 6 and 7) dealt with the problem of antimicrobial resistance in S. aureus, and with the role of biofilms in enhancing this process. Consequently, a novel strategy for the control of S. aureus biofilms was studied and applied. Results obtained represent a starting point for the development of a variety of application dealing with the increase of the shelf-life and the safety of food products.