One of the most important food poisoning bacteria is Campylobacter jejuni - commonly known as "Campy".
The following is from The Bug Bible - http://www.safefood.net.au/AudienceHierarchy/TheBugBible/Default.htm
Campylobacter was not recognised as a cause of foodborne disease until the 1970s, and is now thought to be the main cause of foodborne disease in Australia. It is naturally present in the intestines of a number of different domestic animals and birds. It can be frequently isolated from the surface of poultry and also on the surface of cuts of raw meats. It has also been isolated from raw milk
The organism is sensitive to heat. Adequate cooking, reheating and control of cross contamination from raw foods to cooked foods are the primary control mechanisms in the kitchen. There have been a number of case investigations where salads have been implicated as the source of the organism. Transfer of the organisms to the salad vegetables from surfaces or implements used for raw meats being the most likely cause.