Characterization of rpoS alleles in Escherichia coli O157 : H7 and in other E-coli serotypes

The rpoS nucleotide and predicted amino acid sequences from three Escherich ia roll O157:H7 isolates were compared with those from three other E, coli isolates, including the likely O157:H7 progenitor, E. coli O55:H7. These cl inical and environmental isolates all had identical sigma(S) amino acid seq uences, while laboratory strains K12 and DH1 had three and one amino acid a lterations, respectively, in comparison with the majority sequence. To exte nd the analysis of sigma(S) sequence conservation to include other Gram-neg ative bacteria, the E. loll sigma(S) sequences were compared with those fro m diverse Gram-negative organisms; sigma(S) sequence identities ranged from 50.2 to 99.7% among the available sequences. The results further confirm t he existence of rpoS alleles among different E. coli strains, although all strains were classified as acid-resistant with survival rates > 10% after 2 h exposure to pH 2.5. It was also found that all E. coli O157:H7 isolates tested had a unique nucleotide at position 543, thus differentiating these strains from other E. coli serotypes.