Bacterial strains are specific variations of bacteria that have distinct genetic, biochemical, or phenotypic characteristics. These strains can arise from mutations, genetic recombination, or environmental adaptations, leading to differences in their behavior, pathogenicity, or resistance to antibiotics. Researchers often study bacterial strains to understand their roles in health, disease, and ecosystems. For example, Escherichia coli has numerous strains, some of which are harmless and part of the normal gut flora, while others can cause serious infections. Identifying and classifying these strains is crucial for developing effective treatments and public health strategies.