Identification of Escherichia coli O-serogroups by restriction of the amplified O-antigen gene cluster (rfb-RFLP)

The precise serotyping of clinical Escherichia coli isolates is a crucial s tep for diagnostic and epidemiological purposes. Epidemiological knowledge associated with serotyping is so important that no alternative method may b e considered if it does not correlate with serotyping. Unfortunately, E. co li are difficult to serotype. Genes specifically involved in O-antigen synt hesis are clustered in E. coli, Shigella and Salmonella. Published oligonuc leotide sequences complementary to JUMPstart and the gnd gene (the conserve d flanking sequences upstream and downstream of O-antigen gene clusters, re spectively) were used to amplify the O-antigen gene cluster of representati ve strains of 148 E. coli O-serogroups. A unique amplified fragment was obs erved for each serogroup (size ranging from 1.7 to 20 kbp). Clearly identif iable and reproducible O-patterns were obtained for the great majority of O -serogroups after MboII digestion of amplified products. The number of band s composing each pattern varied from five to 25. A database was built with the patterns obtained. A total of 147 O-patterns were obtained. Thirteen O- serogroups were subdivided into different O-patterns. However, each of 13 o ther O-patterns was shared by two or more O-serogroups. O-serogroups of cli nical isolates were deduced accurately from O-patterns in all cases, even f or some rough or nonagglutinating isolates. The restriction method (rfb-RFL P) may prove to be better than serotyping since 100% of strains are typable , which is not the case with serotyping. (C) 2000 Editions scientifiques et medicales Elsevier SAS.