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, bacteria are cells - they are larger but they 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 to 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 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. This is due to their overuse which can lead to the development of antibiotic resistant bacteria.
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.
Agrobacterium tumefaciens is a bacterium species that causes crown gall disease in plants. This is like cancer and a tumour develops where the bacterium has infected the plant. Often the tumours appear in the stems or roots of the plants. Many plant species can be infected by the bacterium and so it is a huge concern for farmers.
Agrobacterium tumefaciens transfers some of its own DNA to the infected plant cell's DNA. This means that scientists can test the DNA of the infected plant to see if it has been infected by Agrobacterium tumefaciens and confirm that the disease is crown gall disease.