title: Phylogeny and strain typing of Escherichia coli, inferred from variation at mononucleotide repeat loci.
abstract: Multilocus sequencing of housekeeping genes has been used previously for bacterial strain typing and for inferring evolutionary relationships among strains of Escherichia coli. In this study, we used shorter intergenic sequences that contained simple sequence repeats (SSRs) of repeating mononucleotide motifs (mononucleotide repeats [MNRs]) to infer the phylogeny of pathogenic and commensal E. coli strains. Seven noncoding loci (four MNRs and three non-SSRs) were sequenced in 27 strains, including enterohemorrhagic (six isolates of O157:H7), enteropathogenic, enterotoxigenic, B, and K-12 strains. The four MNRs were also sequenced in 20 representative strains of the E. coli reference (ECOR) collection. Sequence polymorphism was significantly higher at the MNR loci, including the flanking sequences, indicating a higher mutation rate in the sequences flanking the MNR tracts. The four MNR loci were amplifiable by PCR in the standard ECOR A, B1, and D groups, but only one (yaiN) in the B2 group was amplified, which is consistent with previous studies that suggested that B2 is the most ancient group. High sequence compatibility was found between the four MNR loci, indicating that they are in the same clonal frame. The phylogenetic trees that were constructed from the sequence data were in good agreement with those of previous studies that used multilocus enzyme electrophoresis. The results demonstrate that MNR loci are useful for inferring phylogenetic relationships and provide much higher sequence variation than housekeeping genes. Therefore, the use of MNR loci for multilocus sequence typing should prove efficient for clinical diagnostics, epidemiology, and evolutionary study of bacteria.
authors.affiliation: Department of Food Engineering and Biotechnology, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Eran
authors.initials: E
authors.lastname: Diamant
authors.forename: Yniv
authors.initials: Y
authors.lastname: Palti
authors.forename: Riva
authors.initials: R
authors.lastname: Gur-Arie
authors.forename: Helit
authors.initials: H
authors.lastname: Cohen
authors.forename: Eric M
authors.initials: EM
authors.lastname: Hallerman
authors.forename: Yechezkel
authors.initials: Y
authors.lastname: Kashi
mesh_terms: D015373:Bacterial Typing Techniques; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000145:classification* / Q000235:genetics* / Q000472:pathogenicity; D019453:Escherichia coli O157 / Q000145:classification / Q000235:genetics / Q000472:pathogenicity; D014644:Genetic Variation; D006801:Humans; D018895:Microsatellite Repeats; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D012703:Serotyping
chemical_list: D017931:DNA Primers; D004269:DNA, Bacterial