MboII endonuclease heat inactivation before agarose gel electrophoresis to prevent artifactual bands in restriction patterns

Identification of major Streptococcal species by rrn-amplified ribosomal DNA restriction analysis

Amplified ribosomal DNA restriction analysis (rrn-ARDRA) is based on PCR amplification and restriction of a fragment of rRNA genes including 16S and 23S genes and the intergenic spacer. rrn-ARDRA was evaluated for the identification of species within the genus Streptococcus: A total of 148 type and reference strains of pyogenic, oral, and group D streptococci were examined in order to construct a database for identification of streptococci. The amplified product was a single band approximately 4500 bp long. This amplicon was digested separately with three (HhaI, MboII, and Sau3A) restriction endonucleases. Respectively, 27, 26, and 28 major patterns were observed after HhaI, MboII, and Sau3A restrictions. Streptococcal strains belonging to different species had different patterns or different combination of patterns. An identification system based upon a combination of the three restriction patterns in a single database was then proposed. rrn-ARDRA was successfully applied to 11 clinical isolates whose identification to the species level was difficult to obtain by phenotypic analysis. Using a database of well-characterized strains, rrn-ARDRA is a powerful method for the identification of streptococcal isolates.

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 step for diagnostic and epidemiological purposes. Epidemiological knowledge associated with serotyping is so important that no alternative method may be considered if it does not correlate with serotyping. Unfortunately, E. coli are difficult to serotype. Genes specifically involved in O-antigen synthesis are clustered in E. coli, Shigella and Salmonella. Published oligonucleotide sequences complementary to JUMPstart and the gnd gene (the conserved flanking sequences upstream and downstream of O-antigen gene clusters, respectively) were used to amplify the O-antigen gene cluster of representative strains of 148 E. coli O-serogroups. A unique amplified fragment was observed for each serogroup (size ranging from 1.7 to 20 kbp). Clearly identifiable and reproducible O-patterns were obtained for the great majority of O-serogroups after MboII digestion of amplified products. The number of bands 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 other O-patterns was shared by two or more O-serogroups. 0-serogroups of clinical isolates were deduced accurately from O-patterns in all cases, even for some rough or nonagglutinating isolates. The restriction method (rfb-RFLP) may prove to be better than serotyping since 100% of strains are typable, which is not the case with serotyping.