Bacterial strains refer to distinct genetic variants or subtypes within a species of bacteria. These strains can exhibit different characteristics, such as varying resistance to antibiotics, pathogenicity, or metabolic capabilities. Understanding these differences is crucial for fields like microbiology and medicine, as specific strains can cause different diseases or respond differently to treatments. Researchers often study bacterial strains to track outbreaks and develop vaccines. For example, the Escherichia coli species has numerous strains, some of which are harmless, while others can lead to severe foodborne illnesses. Identifying and classifying these strains helps in managing public health risks effectively.