Print

Science

Defending against infection

Pathogens are microorganisms - such as bacteria and viruses - that cause disease. Bacteria release toxins, and viruses damage our cells. White blood cells can ingest and destroy pathogens. They can produce antibodies to destroy pathogens, and antitoxins to neutralise toxins.

In vaccination pathogens are introduced into the body in a weakened form. The process causes the body to produce enough white blood cells to protect itself against the pathogens, while not getting diseased.

Antibiotics are effective against bacteria, but not against viruses. Some strains of bacteria are resistant to antibiotics.

Pathogens - bacteria

Pathogens are microorganisms that cause infectious disease. Bacteria and viruses are the main pathogens.

Bacteria

a salmonella bacterium cell

Structure of a salmonella bacterium cell

Bacteria are microscopic organisms. They come in many shapes and sizes, but even the largest are only 10 micrometres long - 10 millionths of a metre.

Bacteria are living cells and, in favourable conditions, can multiply rapidly. Once inside the body, they release poisons or toxins that make us feel ill. Diseases caused by bacteria include:

  • food poisoning
  • cholera
  • typhoid
  • whooping cough
  • gonorrhoea - a sexually transmitted disease

Back to Human biology index

BBC navigation

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.