Ribosomal-RNA patterns of Escherichia coli, Salmonella typhimurium and related Enterobacteriaceae

rRNA sequences are usually highly conserved among species. In Enterobacteriaceae we have shown that Salmonella typhimurium does not have an equivalent to the 23S rRNA of Escherichia coli but its 23S rRNA is cleaved in vivo into two smaller species. This cleavage appears to be a result of a difference between the S. typhimurium and E. coli rRNA sequences rather than to differences in ribonuclease activity. We have surveyed a wide range of Enterobacteriaceae for the presence or absence of 23S rRNA and found this rRNA species to be present in all strains of E. coli, Shigella and Citrobacter and all salmonellae examined except S. typhimurium. All S. typhimurium cultures, isolated at different times and from several different countries, lack an intact 23S rRNA. Thus, the presence or absence of this rRNA species is an excellent diagnostic characteristic for S. typhimurium.