Biocides have been widely used for several decades to preserve materials including food and cosmetics, to decontaminate surfaces, to disinfect instruments, used in fabrics and, even, in toys, for personal hygiene, and to prevent transmission of infections. Nevertheless, when used in large volumes or at high concentrations, biocides have toxic effects and excessive use is dangerous for the environment, including animals and humans. Despite this widespread and ever increasing use of biocides, most bacterial and fungal species remain susceptible but decreased susceptibility has been reported and occasionally linked to antibiotic resistance, mainly in human and veterinary pathogens.

The problem of the development of resistances, together with the possibility to prevent them, has been carefully considered by the EC in the Biocides Directive 98/8/CE, a norm which oversees a high protection for the environment and man, and harmonizes the rules for placing on the market within the European Union any active substances and biocidal products.

This work is developed in the context of the European project BIOHYPO (Proposal No 227258 of the Programme ``FP7 Cooperation Work Programme: Food, Agriculture and Fisheries, and Biotechnologies'') (Dr. Marco Oggioni, PI). The main goal is the evaluation of the risk for clinically significant increase or spread of antibiotic resistance in food pathogens due to biocide use. Statistical analyses are performed in a large data set of Staphylococcus aureus in order to have insight about the real clinical relevance of any antibiotic/biocide co- and cross-resistance.