THERE are thousands of food borne bacteria and viruses capable of causing the familiar, unwelcome symptoms of food poisoning. Our immune systems are generally able to defeat them but occasionally illness results from exposure to these agents. A rogues gallery of the most common bugs would include the following:

. Campylobacter - bacteria commonly found in poultry, infection caused by under cooking, or raw foods contaminating cooked foods

. Salmonella group - more than 2,000 strains in this bacteria family which is found in poultry and other animal derived foods, eggs and unpasteurised milk. The most common forms include salmonella enteritidis and salmonella typhimurium

. Listeria monocytogenes - bacteria found in a range of foods including soft cheeses and cooked chilled foods, particularly dangerous when they affect women during pregnancy and patients with weakened immune systems

. E coil 0157:H7 - bacteria which, like other E coli types, are found in intestinal tracts; responsible for an outbreak in Scotland which killed 19 - infection arose after meat was contaminated during slaughter

. Staphylococcus aureus - very common bacteria carried by half of population on hands or in nasal passages

. Clostridium hotulinum - bacteria that grow in absence of oxygen, occasionally contaminating tinned or vacuum packed foods. As they multiply, they produce toxins which are powerful enough to cause death

. Clostridium perfringens - far less dangerous bacteria than clostridium botulinum, most frequently occur in bulk cooked foods which are then improperly reheated

. Bacillus cereus - bacteria that thrive on high carbohydrate foods such as boiled or fried rice and cereals

. Viruses - hundreds of types, thought to cause at least as much food related illness as bacteria, but are more difficult to identify