Escherichia coli serotype O55:H7 diversity supports parallel acquisition of bacteriophage at Shiga toxin phage insertion sites during evolution of the O157:H7 lineage.
Enteropathogenic Escherichia coli (EPEC) continues to be a leading cause of mortality and morbidity in children around the world. Two EPEC genomes have been fully sequenced: those of EPEC O127:H6 strain E2348/69 (United Kingdom, 1969) and EPEC O55:H7 strain CB9615 (Germany, 2003). The O55:H7 serotype is a recent precursor to the virulent enterohemorrhagic E. coli O157:H7. To explore the diversity of O55:H7 and better understand the clonal evolution of O157:H7, we fully sequenced EPEC O55:H7 strain RM12579 (California, 1974), which was collected 1 year before the first U.S. isolate of O157:H7 was identified in California. Phage-related sequences accounted for nearly all differences between the two O55:H7 strains. Additionally, O55:H7 and O157:H7 strains were tested for the presence and insertion sites of Shiga toxin gene (stx)-containing bacteriophages. Analysis of non-phage-associated genes supported core elements of previous O157:H7 stepwise evolutionary models, whereas phage composition and insertion analyses suggested a key refinement. Specifically, the placement and presence of lambda-like bacteriophages (including those containing stx) should not be considered stable evolutionary markers or be required in placing O55:H7 and O157:H7 strains within the stepwise evolutionary models. Additionally, we suggest that a 10.9-kb region (block 172) previously believed unique to O55:H7 strains can be used to identify early O157:H7 strains. Finally, we defined two subsets of O55:H7 strains that share an as-yet-unobserved or extinct common ancestor with O157:H7 strains. Exploration of O55:H7 diversity improved our understanding of the evolution of E. coli O157:H7 and suggested a key revision to accommodate existing and future configurations of stx-containing bacteriophages into current models.
Produce Safety and Microbiology Research Unit, Western Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Albany, California, USA.
Jennifer L
JL
Kyle
Craig A
CA
Cummings
Craig T
CT
Parker
Beatriz
B
Quiñones
Paolo
P
Vatta
Elizabeth
E
Newton
Steven
S
Huynh
Michelle
M
Swimley
Lovorka
L
Degoricija
Melissa
M
Barker
Samar
S
Fontanoz
Kimberly
K
Nguyen
Ronak
R
Patel
Rixun
R
Fang
Robert
R
Tebbs
Olga
O
Petrauskene
Manohar
M
Furtado
Robert E
RE
Mandrell
D001435:Bacteriophages; D002876:Chromosomes, Bacterial; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics; D054308:Enteropathogenic Escherichia coli / Q000145:classification / Q000235:genetics*; D019453:Escherichia coli O157 / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D005819:Genetic Markers; D014644:Genetic Variation; D016680:Genome, Bacterial; D008969:Molecular Sequence Data; D010802:Phylogeny; D012703:Serotyping; D022621:Shiga Toxin / Q000235:genetics*
D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D005819:Genetic Markers; D022621:Shiga Toxin