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In silico genomic analyses reveal three distinct lineages of Escherichia coli O157:H7, one of which is associated with hyper-virulence.

ABSTRACT: BACKGROUND: Many approaches have been used to study the evolution, population structure and genetic diversity of Escherichia coli O157:H7; however, observations made with different genotyping systems are not easily relatable to each other. Three genetic lineages of E. coli O157:H7 designated I, II and I/II have been identified using octamer-based genome scanning and microarray comparative genomic hybridization (mCGH). Each lineage contains significant phenotypic differences, with lineage I strains being the most commonly associated with human infections. Similarly, a clade of hyper-virulent O157:H7 strains implicated in the 2006 spinach and lettuce outbreaks has been defined using single-nucleotide polymorphism (SNP) typing. In this study an in silico comparison of six different genotyping approaches was performed on 19 E. coli genome sequences from 17 O157:H7 strains and single O145:NM and K12 MG1655 strains to provide an overall picture of diversity of the E. coli O157:H7 population, and to compare genotyping methods for O157:H7 strains. RESULTS: In silico determination of lineage, Shiga-toxin bacteriophage integration site, comparative genomic fingerprint, mCGH profile, novel region distribution profile, SNP type and multi-locus variable number tandem repeat analysis type was performed and a supernetwork based on the combination of these methods was produced. This supernetwork showed three distinct clusters of strains that were O157:H7 lineage-specific, with the SNP-based hyper-virulent clade 8 synonymous with O157:H7 lineage I/II. Lineage I/II/clade 8 strains clustered closest on the supernetwork to E. coli K12 and E. coli O55:H7, O145:NM and sorbitol-fermenting O157 strains. CONCLUSION: The results of this study highlight the similarities in relationships derived from multi-locus genome sampling methods and suggest a "common genotyping language" may be devised for population genetics and epidemiological studies. Future genotyping methods should provide data that can be stored centrally and accessed locally in an easily transferable, informative and extensible format based on comparative genomic analyses.

SUBMITTER: Laing CR

PROVIDER: S-EPMC2719669 | biostudies-literature | 2009

REPOSITORIES: biostudies-literature

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In silico genomic analyses reveal three distinct lineages of Escherichia coli O157:H7, one of which is associated with hyper-virulence.

Laing Chad R CR Buchanan Cody C Taboada Eduardo N EN Zhang Yongxiang Y Karmali Mohamed A MA Thomas James E JE Gannon Victor Pj VP

BMC genomics 20090629

<h4>Background</h4>Many approaches have been used to study the evolution, population structure and genetic diversity of Escherichia coli O157:H7; however, observations made with different genotyping systems are not easily relatable to each other. Three genetic lineages of E. coli O157:H7 designated I, II and I/II have been identified using octamer-based genome scanning and microarray comparative genomic hybridization (mCGH). Each lineage contains significant phenotypic differences, with lineage ...[more]

PMID: 19563677

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Project description:BACKGROUND: Genetic analysis of Escherichia coli O157:H7 strains has shown divergence into two distinct lineages, lineages I and II, that appear to have distinct ecological characteristics, with lineage I strains more commonly associated with human disease. In this study, microarray-based comparative genomic hybridization (CGH) was used to identify genomic differences among 31 E. coli O157:H7 strains that belong to various phage types (PTs) and different lineage-specific polymorphism assay (LSPA) types. RESULTS: A total of 4,084 out of 6,057 ORFs were detected in all E. coli O157:H7 strains and 1,751 were variably present or absent. Based on this data, E. coli O157:H7 strains were divided into three distinct clusters, which consisted of 15 lineage I (LSPA type 111111), four lineage I/II (designated in this study) (LSPA type 211111) and 12 lineage II strains (LSPA 222222, 222211, 222212, and 222221), respectively. Eleven different genomic regions that were dominant in lineage I strains (present in > or =80% of lineage I and absent from > or = 92% of lineage II strains) spanned segments containing as few as two and up to 25 ORFs each. These regions were identified within E. coli Sakai S-loops # 14, 16, 69, 72, 78, 83, 85, 153 and 286, Sakai phage 10 (S-loops # 91, 92 and 93) and a genomic backbone region. All four lineage I/II strains were of PT 2 and possessed eight of these 11 lineage I-dominant loci. Several differences in virulence-associated loci were noted between lineage I and lineage II strains, including divergence within S-loop 69, which encodes Shiga toxin 2, and absence of the non-LEE encoded effector genes nleF and nleH1-2 and the perC homologue gene pchD in lineage II strains. CONCLUSION: CGH data suggest the existence of two dominant lineages as well as LSPA type and PT-related subgroups within E. coli O157:H7. The genomic composition of these subgroups supports the phylogeny that has been inferred from other methods and further suggests that genomic divergence from an ancestral form and lateral gene transfer have contributed to their evolution. The genomic features identified in this study may contribute to apparent differences in the epidemiology and ecology of strains of different E. coli O157:H7 lineages.

Project description:Two lineages of enterohemorrhagic (EHEC) Escherichia coli O157:H7 (EDL933, Stx1+ and Stx2+) and 86-24 (Stx2+) were investigated in regards to biofilm formation on an abiotic surface. Strikingly, EDL933 strain formed a robust biofilm while 86-24 strain formed no biofilm on either a polystyrene plate or a polyethylene tube. To identify the genetic mechanisms of different biofilm formation in two EHEC strains, DNA microarrays were first performed and phenotypic assays were followed. In the comparison of the EDL933 strain versus 86-24 strain, genes (csgBAC and csgDEFG) involved in curli biosynthesis were significantly induced while genes (trpLEDCB and mtr) involved in indole signaling were repressed. Additionally, a dozen of phage genes were differentially present between two strains. Curli assays using a Congo red plate and scanning electron microscopy corroborate the microarray data as the EDL 933 strain produces a large amount of curli, while 86-24 forms much less curli. Also, the indole production in the EDL933 was 2-times lower than that of 86-24. It was known that curli formation positively regulates and indole negatively regulates biofilm formation of EHEC. Hence, it appears that less curli formation and high indole production in the 86-24 strain are majorly responsible for no biofilm formation. For the microarray experiments, E. coli O157:H7 EDL933 and 86-24 were inoculated in 25 ml of LB in 250 ml shake flasks with overnight cultures that were diluted 1:100. Cells were shaken at 250 rpm and 37°C for an absorbance of 4.0 at 600 nm. Cells were immediately chilled with dry ice and 95% ethanol (to prevent RNA degradation) for 30 sec before centrifugation in 50 ml centrifuge tubes at 13,000 g for 2 min; cell pellets were frozen immediately with dry ice and stored -80°C. RNA was isolated using Qiagen RNeasy mini Kit (Valencia, CA, USA). RNA quality was assessed by Agilent 2100 bioanalyser using the RNA 6000 Nano Chip (Agilent Technologies, Amstelveen, The Netherlands), and quantity was determined by ND-1000 Spectrophotometer (NanoDrop Technologies, Inc., DE, USA).

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In silico genomic analyses reveal three distinct lineages of Escherichia coli O157:H7, one of which is associated with hyper-virulence.

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In silico genomic analyses reveal three distinct lineages of Escherichia coli O157:H7, one of which is associated with hyper-virulence.

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