Bacterium

It is a kind of micro-organism that consists of a single cell, and it multiplies by a simple duplication (a single bacterium is able to divide itself giving place to two bacteria). Some of them are pathogenic (Salmonellla, for instance), and other ones live, in normal conditions, inside the body of the living beings without causing any disorder (for instance, intestinal flora). Some "famous" bacteria in the pig world are Escherichia coli (E. coli), Actinobacillus pleuropneumoniae or Pasteurella multocida. As in the cases of the viruses, bacteria are able to survive during a variable period of time outside the body of the animal (days, months, and even years), depending on the environmental conditions (cold and humidity normally increase their survival ability), on the kind of bacteria and on the hygienic conditions.