Conserved genes in enteric bacteria are not identical.

In addition to ribosomal RNA genes, a relatively small number of genes are highly conserved between Escherichia coli and Salmonella typhimurium on the one hand, and either Serratia marcescens or Proteus morganii on the other hand. The conserved non-rRNA genes are not the same in S. marcescens and P. Morganii. Different genetic segments have maintained nucleotide sequence similarity to parts of the E. coli and S. typhimurium genomes in the course of the evolution of S. marcescens and P. morganii.