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Genetic diversity among clonal lineages within Escherichia coli O157:H7 stepwise evolutionary model.

Feng PC, Monday SR, Lacher DW, Allison L, Siitonen A, Keys C, Eklund M, Nagano H, Karch H, Keen J, Whittam TS - Emerging Infect. Dis. (2007)

Bottom Line: Escherichia coli O157:H7 variants were examined for trait mutations and by molecular subtyping to better define clonal complexes postulated on the O157:H7 evolution model.Despite similarities, some Finnish and Scottish and all of the German strains have ST-75 ("German clone"), whereas others have ST-76, a new variant ("Scottish clone").MLST of strains in other clonal complexes also discriminated strains thought to be identical and showed that genetic differences will further distinguish clonal populations into subclones.

View Article: PubMed Central - PubMed

Affiliation: Food and Drug Administration, College Park, Maryland 20740, USA. peter.feng@fda.hhs.gov

ABSTRACT
Escherichia coli O157:H7 variants were examined for trait mutations and by molecular subtyping to better define clonal complexes postulated on the O157:H7 evolution model. Strains of beta-glucuronidase-positive, sorbitol-negative O157:H7 isolated in United States and Japan were identical to A5 clonal strain and shared sequence type (ST)-65 by multilocus sequence typing (MLST); thus, they belong in A5. However, these strains exhibited pulsed-field gel electrophoresis (PFGE) profile differences that suggested genomic divergence between populations. Sorbitol-fermenting O157 (SFO157) strains from Finland, Scotland, and Germany were identical to A4 clonal strain and belong in A4. Some SFO157 strains, isolated years apart and from different countries, had identical PFGE profiles, suggesting a common origin. Despite similarities, some Finnish and Scottish and all of the German strains have ST-75 ("German clone"), whereas others have ST-76, a new variant ("Scottish clone"). MLST of strains in other clonal complexes also discriminated strains thought to be identical and showed that genetic differences will further distinguish clonal populations into subclones.

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Evolution model for Escherichia coli O157:H7. Figure modified and updated from (1) to include the sequence type (ST) data showing subclones within clonal complexes. Some strains, whose position on the model remains to be determined, are shown with dashed lines.
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Figure 3: Evolution model for Escherichia coli O157:H7. Figure modified and updated from (1) to include the sequence type (ST) data showing subclones within clonal complexes. Some strains, whose position on the model remains to be determined, are shown with dashed lines.

Mentions: The stepwise evolutionary model postulates that ancestral O157 clonal group (A3) split into 1 lineage, leading to the common GUD–, SOR– O157:H7 (NSF O157) clonal complex (A6) and a second branch of SFO157 that retained many primitive traits (A4) (Figure 3). The A4 and A5 clonal complexes on the evolution model are closely related to O157:H7 (A6 clonal complex) (Figure 3) and share many traits, including the +93 uidA SNP, which is found only in O157:H7 and its nonmotile variants (1). Another common trait is the γ-eae allele, which is also found in few other serotypes (21), including the O55:H7 strains in the A2 clonal complex that is ancestral to O157:H7 (2) (Figure 3). The A5 clonal complex of GUD+ O157:H7 strains is postulated to have emerged from the A3 intermediate strain. Analysis of A5 type strain (G5101) showed that it carried a +776 uidA SNP, which appears to have been acquired before the emergence of A5, because it is found only in A5 strains and A6 clonal complex of O157:H7 strains (3). All the GUD+ O157:H7 strains tested had identical traits as G5101, including the unique uidA markers (+93 and +776 SNP and absence of +686 G-G insertion) that are consistent with the mutational events postulated for the emergence of A5 and confirm that these strains also belong in A5. The fact that all these GUD+ O157:H7 strains have ST-65 supports that conclusion (Table 2). Despite similarities, however, there were differences in PFGE profiles. The Japanese strains had nearly identical PFGE profiles, which is consistent with the results by Nagano et al. (7), who also observed profile identity among clinical and environmental GUD+ O157:H7 isolates in Japan (22). In contrast, the US strains showed more diversity and shared only 70% similarity with the Japanese strains, which suggests the occurrence of recent genomic divergences among the US populations of GUD+ O157:H7 strains.


Genetic diversity among clonal lineages within Escherichia coli O157:H7 stepwise evolutionary model.

Feng PC, Monday SR, Lacher DW, Allison L, Siitonen A, Keys C, Eklund M, Nagano H, Karch H, Keen J, Whittam TS - Emerging Infect. Dis. (2007)

Evolution model for Escherichia coli O157:H7. Figure modified and updated from (1) to include the sequence type (ST) data showing subclones within clonal complexes. Some strains, whose position on the model remains to be determined, are shown with dashed lines.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3375798&req=5

Figure 3: Evolution model for Escherichia coli O157:H7. Figure modified and updated from (1) to include the sequence type (ST) data showing subclones within clonal complexes. Some strains, whose position on the model remains to be determined, are shown with dashed lines.
Mentions: The stepwise evolutionary model postulates that ancestral O157 clonal group (A3) split into 1 lineage, leading to the common GUD–, SOR– O157:H7 (NSF O157) clonal complex (A6) and a second branch of SFO157 that retained many primitive traits (A4) (Figure 3). The A4 and A5 clonal complexes on the evolution model are closely related to O157:H7 (A6 clonal complex) (Figure 3) and share many traits, including the +93 uidA SNP, which is found only in O157:H7 and its nonmotile variants (1). Another common trait is the γ-eae allele, which is also found in few other serotypes (21), including the O55:H7 strains in the A2 clonal complex that is ancestral to O157:H7 (2) (Figure 3). The A5 clonal complex of GUD+ O157:H7 strains is postulated to have emerged from the A3 intermediate strain. Analysis of A5 type strain (G5101) showed that it carried a +776 uidA SNP, which appears to have been acquired before the emergence of A5, because it is found only in A5 strains and A6 clonal complex of O157:H7 strains (3). All the GUD+ O157:H7 strains tested had identical traits as G5101, including the unique uidA markers (+93 and +776 SNP and absence of +686 G-G insertion) that are consistent with the mutational events postulated for the emergence of A5 and confirm that these strains also belong in A5. The fact that all these GUD+ O157:H7 strains have ST-65 supports that conclusion (Table 2). Despite similarities, however, there were differences in PFGE profiles. The Japanese strains had nearly identical PFGE profiles, which is consistent with the results by Nagano et al. (7), who also observed profile identity among clinical and environmental GUD+ O157:H7 isolates in Japan (22). In contrast, the US strains showed more diversity and shared only 70% similarity with the Japanese strains, which suggests the occurrence of recent genomic divergences among the US populations of GUD+ O157:H7 strains.

Bottom Line: Escherichia coli O157:H7 variants were examined for trait mutations and by molecular subtyping to better define clonal complexes postulated on the O157:H7 evolution model.Despite similarities, some Finnish and Scottish and all of the German strains have ST-75 ("German clone"), whereas others have ST-76, a new variant ("Scottish clone").MLST of strains in other clonal complexes also discriminated strains thought to be identical and showed that genetic differences will further distinguish clonal populations into subclones.

View Article: PubMed Central - PubMed

Affiliation: Food and Drug Administration, College Park, Maryland 20740, USA. peter.feng@fda.hhs.gov

ABSTRACT
Escherichia coli O157:H7 variants were examined for trait mutations and by molecular subtyping to better define clonal complexes postulated on the O157:H7 evolution model. Strains of beta-glucuronidase-positive, sorbitol-negative O157:H7 isolated in United States and Japan were identical to A5 clonal strain and shared sequence type (ST)-65 by multilocus sequence typing (MLST); thus, they belong in A5. However, these strains exhibited pulsed-field gel electrophoresis (PFGE) profile differences that suggested genomic divergence between populations. Sorbitol-fermenting O157 (SFO157) strains from Finland, Scotland, and Germany were identical to A4 clonal strain and belong in A4. Some SFO157 strains, isolated years apart and from different countries, had identical PFGE profiles, suggesting a common origin. Despite similarities, some Finnish and Scottish and all of the German strains have ST-75 ("German clone"), whereas others have ST-76, a new variant ("Scottish clone"). MLST of strains in other clonal complexes also discriminated strains thought to be identical and showed that genetic differences will further distinguish clonal populations into subclones.

Show MeSH
Related in: MedlinePlus