Adenine and thymine homopolymer strings of at least 8 nucleotides (AT 8+mers) were charac-terized in Salmonella enterica subspecies I and other Eubacteria. Incidence of the motif differed between Eubacteria but not between Salmonella enterica serotypes. Of 481 AT 8+mers loci in serovars Typhimurium, Enteritidis, and Gallinarum, 35 (12.3%) had mutations. We propose that the AT 8+mer motif identifies genomes with optimal gene content and provides self-recognition that facilitates efficient genome repair. A theory that genome regeneration accounts for both serovar diversity and persistence of predominant Salmonella serovars associated provides a new framework for investigating root causes of foodborne illness.