Strains

Strains are genetic variants or lineages within a species that are distinguishable by stable differences in genotype or phenotype. In microbiology and related fields, a strain refers to a population descended from a common ancestor and maintained as a distinct, identifiable unit.

Strains arise through mutation, genetic recombination, horizontal gene transfer, and selective pressures such as host immunity or antimicrobial use. Once a lineage becomes stable and reproducible, it can be propagated as a discrete strain across laboratories and environments.

The term is descriptive rather than strictly taxonomic; it is widely used for bacteria, viruses, fungi, and even plants or algae to denote meaningful genetic or phenotypic differences within a species.

Typing and identification methods include whole-genome sequencing, multilocus sequence typing (MLST), serotyping, and fingerprinting techniques. These tools help researchers track transmission, study evolution, and select appropriate strains for experiments or vaccines.

The clinical and ecological relevance of strains varies: some strains carry particular virulence factors or antibiotic resistance genes; others are better adapted to specific hosts or environments. In agriculture, strain designation can relate to traits such as growth rate or stress tolerance.

Boundaries between strains are not always sharp. Differences can be continuous, and naming conventions differ among fields, institutions, and databases. A strain designation may be redundant or revised as new data emerge.

Examples include bacterial strains such as Escherichia coli O157:H7, viral strains such as influenza strains, and laboratory or agricultural strains used as reference isolates.