Strain (biology) Microbiology/Virology
A strain is a genetic variant or subtype of a microorganism, that is to say a virus or bacterium or fungus. Properly speaking, Bacteria, Archaea and viruses do not have species, because they do not have eukaryote-type sexual reproduction. Even though, for historical reasons, common types such as 'Staphlococcus aureus' were given double names. Bacteria do exchange DNA, but they may exchange it between different kinds of bacteria, illustrating their considerable difference from eukaryotes. Strains are therefore an absolutely essential part of bacterial identification.