Cryptic lineages of the genus Escherichia.
Extended multilocus sequence typing (MLST) analysis of atypical Escherichia isolates was used to identify five novel phylogenetic clades (CI to CV) among isolates from environmental, human, and animal sources. Analysis of individual housekeeping loci showed that E. coli and its sister clade, CI, remain largely indistinguishable and represent nascent evolutionary lineages. Conversely, clades of similar age (CIII and CIV) were found to be phylogenetically distinct. When all Escherichia lineages (named and unnamed) were evaluated, we found evidence that Escherichia fergusonii has evolved at an accelerated rate compared to E. coli, CI, CIII, CIV, and CV, suggesting that this species is younger than estimated by the molecular clock method. Although the five novel clades were phylogenetically distinct, we were unable to identify a discriminating biochemical marker for all but one of them (CIII) with traditional phenotypic profiling. CIII had a statistically different phenotype from E. coli that resulted from the loss of sucrose and sorbitol fermentation and lysine utilization. The lack of phenotypic distinction has likely hindered the ability to differentiate these clades from typical E. coli, and so their ecological significance and importance for applied and clinical microbiology are yet to be determined. However, our sampling suggests that CIII, CIV, and CV represent environmentally adapted Escherichia lineages that may be more abundant outside the host gastrointestinal tract.
Walk
Seth T
ST
Department of Internal Medicine, University of Michigan Health System, 4618 Medical Science Building II, Ann Arbor, MI 48109, USA. sethwalk@umich.edu
Alm
Elizabeth W
EW
Gordon
David M
DM
Ram
Jeffrey L
JL
Toranzos
Gary A
GA
Tiedje
James M
JM
Whittam
Thomas S
TS
D000222:Adaptation, Physiological; D000818:Animals; D015373:Bacterial Typing Techniques; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D017753:Ecosystem; D004783:Environmental Microbiology; D004925:Escherichia / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification / Q000502:physiology; D004926:Escherichia coli / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology; D019143:Evolution, Molecular; D041981:Gastrointestinal Tract / Q000382:microbiology; D051456:Gene Flow; D005798:Genes, Bacterial; D006801:Humans; D010641:Phenotype; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D013997:Time Factors
D017931:DNA Primers; D004269:DNA, Bacterial
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