Relationship between O-antigen subtypes, bacterial surface structures and O-antigen gene clusters in Escherichia coli O123 strains carrying genes for Shiga toxins and intimin Lothar Beutin, 1 Quan Wang, 2,3 Dieter Naumann, 4 Weiqing Han, 2,3 Gladys Krause, 1 Luciana Leomil, 5 Lei Wang 2,3 and Lu Feng 2,3 Correspondence Lu Feng fenglu63@nankai.edu.cn 1 National Reference Laboratory for Escherichia coli, Centre for Infectiology and Pathogen Characterization, Federal Institute for Risk Assessment (BfR), Diedersdorfer Weg 1, D-12277 Berlin, Germany 2 TEDA School of Biological Sciences and Biotechnology, Nankai University, 23 HongDa Street, TEDA, Tianjin 300457, P. R. China 3 Tianjin Key Laboratory for Microbial Functional Genomics, TEDA College, Nankai University, 23 HongDa Street, TEDA, Tianjin 300457, P. R. China 4 Robert Koch Institute, P13, Nordufer 20, D-13353 Berlin, Germany 5 Departamento de Microbiologia, Instituto de Cie ˆ ncias Biome ´ dicas II, Universidade de Sa ˜o Paulo, 05508-900, Sa ˜ o Paulo, SP, Brazil Received 12 June 2006 Accepted 14 September 2006 Escherichia coli O123 strains express a broad spectrum of phenotypes, H serotypes and virulence markers and are able to colonize and to cause disease in different hosts including humans. In this study, two subtypes of E. coli O123 antigen (group I and group II) have been identified based on their cross-reactions with other E. coli O antigens. Investigation of the relationship between O123 group I and group II strains by O serotyping and Fourier transform infrared spectroscopy of whole bacteria revealed surface structural differences between these two groups of E. coli O123 strains. Nucleotide sequence analysis of the O-antigen gene clusters of two E. coli O123 strains representing O123 group I and group II revealed no change at the amino acid level. These findings indicate that the differences in the surface structures of group I and group II strains are not related to genetic heterogeneity in their O-antigen gene clusters. A PCR assay based on O123 antigen-specific wzx and wzy genes was developed and found to be suitable for reliable detection of all subtypes of E. coli O123 strains, which bears an advantage over traditional serological detection. INTRODUCTION The O antigen, which consists of many repeats of an oligosaccharide unit (O unit), is the outer component of LPS in the surface of Gram-negative bacteria (Reeves & Wang, 2002). Due to the presence of different sugars and sugar linkages, it is one of the most variable cell constituents which plays an important role in bacterial evasion of host defence systems (Reeves, 1995). Genes involved in O-antigen synthesis are normally clustered between two housekeeping genes, galF and gnd, in Escherichia coli, and are commonly classified into three main classes: sugar biosynthetic pathway genes, sugar transferase genes and O-antigen processing genes including the flippase (Wzx) and polymerase (Wzy) genes (Reeves & Wang, 2002). Genes encoding Wzx and Wzy are normally specific to different O antigens, and can be used for the development of a PCR assay for the identification and detection of individual strains. Most O- antigen gene clusters have a low G+C content, and it has been proposed that the O-antigen gene cluster was acquired by transfer from other low G+C content species (Wang & Reeves, 2000). The E. coli serogroup O123 was defined by Orskov in 1952 with prototype strain 43w isolated from blood of a calf with Abbreviations: AEEC, attaching and effacing Escherichia coli; FT-IR, Fourier transform infrared; STEC, Shiga toxin-producing Escherichia coli. The GenBank/EMBL/DDBJ accession numbers for the sequences of the E. coli O123 strains 43w and CB9827 O-antigen gene clusters are DQ676933 and DQ676934, respectively. 46775 G 2007 SGM Printed in Great Britain 177 Journal of Medical Microbiology (2007), 56, 177–184 DOI 10.1099/jmm.0.46775-0