Genotyping and characterization of bacterial isolates are essential steps in the identification and control of antibiotic-resistant bacterial infections. Recently, one novel genotyping method using three genomic guided Escherichia coli markers (GIG-EM), dinG, tonB, and dipeptide permease (DPP), was reported. Because GIG-EM has not been fully evaluated using clinical isolates, we assessed this typing method with 72 E. coli collection of reference (ECOR) environmental E. coli reference strains and 63 E. coli isolates of various genetic backgrounds. In this study, we designated 768 bp of dinG, 745 bp of tonB, and 655 bp of DPP target sequences for use in the typing method. Concatenations of the processed marker sequences were used to draw GIG-EM phylogenetic trees. E. coli isolates with identical sequence types as identified by the conventional multilocus sequence typing (MLST) method were localized to the same branch of the GIG-EM phylogenetic tree. Sixteen clinical E. coli isolates were utilized as test isolates without prior characterization by conventional MLST and phylogenetic grouping before GIG-EM typing. Of these, 14 clinical isolates were assigned to a branch including only isolates of a pandemic clone, E. coli B2-ST131-O25b, and these results were confirmed by conventional typing methods. Our results suggested that the GIG-EM typing method and its application to phylogenetic trees might be useful tools for the molecular characterization and determination of the genetic relationships among E. coli isolates.
Several species of antibiotic-resistant bacteria have been found to be causative agents in frequent nosocomial infections. To understand and contain nosocomial infections, the genetic relationships between the causative bacterial isolates need to be identified. To this end, many analytical methods have been developed, including pulsed-field gel electrophoresis (PFGE) (1), ribotyping (2), arbitrarily primed PCRs, such as enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR) and repetitive element sequence-based PCR (rep-PCR) (3), and several multilocus sequence typing (MLST) schemes (4-7).PFGE and ribotyping are principally based on restriction fragment length polymorphisms (RFLP). PFGE in particular has been utilized as one of the gold standard methods, because standard protocols for certain pathogens, such as Escherichia coli serotype O157, have been established and are available online at the PulseNet website (Centers for Disease Control and Prevention, USA) (8). It is relatively simple to obtain reproducible results, i.e., PFGE banding patterns, and perform comparisons of the consequent PFGE banding patterns among test isolates. However, it may be difficult to detect intrachromosomal rearrangements and recombination. PFGE is applicable for an assessment of clonality among test isolates but may not be suitable for considerations of genetic ancestor-descendant relationships.Both ERIC-PCR and rep-PCR target repetitive DNA sequence elements, which are sporadically located throughout the bacteria...