Escherichia coli O123 O antigen genes and polysaccharide structure are conserved in some Salmonella enterica serogroups

This study examined O antigen gene clusters in Salmonella enterica strains and their relationship to Escherichia coli O123. Researchers sequenced O antigen regions from three S. enterica isolates: two serogroup O58 strains and one O41 strain. Both S. enterica O58 isolates shared approximately 85% DNA identity with E. coli O123 O antigen clusters, suggesting evolution from a common ancestor. Gene organization and order were strictly conserved between these organisms. The O41 strain showed more complex evolutionary history, with partial homology to E. coli O123 and significant identity to an O62 strain, particularly in the wzx and wzy genes involved in O antigen polymerization. Serological cross-reactions confirmed that E. coli O123 and Salmonella O58 possess identical or nearly identical O antigens. Chemical analysis of E. coli O123 polysaccharide structure was consistent with predicted compositions based on gene cluster analysis. The findings highlight that wzx and wzy genes alone cannot distinguish between certain serogroups for molecular serotyping, as these genes may be shared between different O serogroups. Understanding both genetic and chemical structures is essential for developing reliable molecular serotyping methods.

Key findings

• Salmonella O58 and E. coli O123 O antigen gene clusters share 85% DNA identity with conserved gene organization, indicating evolution from a common ancestor
• E. coli O123 and Salmonella O58 produce serologically cross-reactive O antigens that are identical or nearly identical
• Salmonella O41 has complex evolutionary history with shared wzx and wzy genes with O62 strains, making these genes unsuitable for differentiating between these serogroups
• Gene cluster composition predicts production of specialized sugars including N-acetyl-quinovosamine and viosamine in the O antigen repeat units
• Chemical structure of E. coli O123 polysaccharide matched predictions from O antigen gene cluster sequence analysis