Campylobacter food poisoning. Composite image of a microbiologist holding a petri dish containing a culture of Campylobacter sp. bacteria and cooked chicken. Campylobacter sp. bacteria are Gram-negative, spiral-shaped bacteria. They are a major cause of foodborne illness in the UK. In humans, infection is commonly caused by the improper handling and preparation of contaminated poultry. Infection causes diarrhoea and inflammation.