Contamination of food and feeds by spoilage or pathogenic microorganism can make many of them no more edible or affect their taste by the production of undesirable flavours. In some cases the activity of these microorganisms can lead to the formation of toxic substances, hazardous to human and animal health, In the past, control of food safety has been carried out by testing both raw and processed samples without any control of the processing.'Recently, instead, the Hazard Analysis Critical Control Point (HACCP)* system have been applied to identify the steps where hazards could occur within the processing, in order to perform and implement monitoring procedures. The subsequent cultural detection methodology, which consists in growing the microorganisms on selective media, is time consuming, since it requires several days from isolation to identification, and expensive.'