STRAINS VERSUS SPECIES. “This is a stunning amount of variation within one “species” of bacteria. (Strains in the genus Shigella are now regarded as E. coli variants that need reclassification). If only strains currently named E. coli are considered, the number of core gene families rises from 993 to 1472, a slight increase of 6 % to 9 % of the total pan-genome.”
https://standardsingenomics.biomedcentral.com/articles/10.1186/s40793-016-0180-8