Not all bacteria are pathogens which cause disease. Many bacteria, like those found in the intestines, are useful. All bacteria are prokaryotes, and do not have a nucleus. Unlike viruses, they are cells and so are larger but cannot be seen without a microscope.
Gonorrhoea is a sexually transmitted disease (STD) caused by a bacterium. It is a common infection, especially amongst people aged 15-24.
Gonorrhoea causes a burning pain when urinating and often forms a thick yellow or green discharge from an infected person's penis or vagina. If untreated it can result in infertility. To prevent infection, people can abstain from having anal, oral or vaginal sex or use a barrier-type of contraception like a condom. Gonorrhoea is treated by antibiotics, though some scientists believe that these antibiotics may one day stop working.
Salmonella is a genus of bacteria that causes food poisoning. This often means abdominal cramps, vomiting and diarrhoea. It is often found in unhygienic kitchens, undercooked foods such as meat, eggs and poultry, or the same foods that have not been reheated properly. To prevent the spread of salmonella in the UK, all poultry are vaccinated against it. Cooking food thoroughly, after preparing it in hygienic conditions, is the best way to avoid illness.