title: aes, the gene encoding the esterase B in Escherichia coli, is a powerful phylogenetic marker of the species.
abstract: BACKGROUND
  Previous studies have established a correlation between electrophoretic polymorphism of esterase B, and virulence and phylogeny of Escherichia coli. Strains belonging to the phylogenetic group B2 are more frequently implicated in extraintestinal infections and include esterase B2 variants, whereas phylogenetic groups A, B1 and D contain less virulent strains and include esterase B1 variants. We investigated esterase B as a marker of phylogeny and/or virulence, in a thorough analysis of the esterase B-encoding gene.
  
  
  RESULTS
  We identified the gene encoding esterase B as the acetyl-esterase gene (aes) using gene disruption. The analysis of aes nucleotide sequences in a panel of 78 reference strains, including the E. coli reference (ECOR) strains, demonstrated that the gene is under purifying selection. The phylogenetic tree reconstructed from aes sequences showed a strong correlation with the species phylogenetic history, based on multi-locus sequence typing using six housekeeping genes. The unambiguous distinction between variants B1 and B2 by electrophoresis was consistent with Aes amino-acid sequence analysis and protein modelling, which showed that substituted amino acids in the two esterase B variants occurred mostly at different sites on the protein surface. Studies in an experimental mouse model of septicaemia using mutant strains did not reveal a direct link between aes and extraintestinal virulence. Moreover, we did not find any genes in the chromosomal region of aes to be associated with virulence.
  
  
  CONCLUSIONS
  Our findings suggest that aes does not play a direct role in the virulence of E. coli extraintestinal infection. However, this gene acts as a powerful marker of phylogeny, illustrating the extensive divergence of B2 phylogenetic group strains from the rest of the species.
authors.affiliation: INSERM U722 and Université Paris 13, Paris, France. mathilde.lescat@inserm.fr
authors.forename: Mathilde
authors.initials: M
authors.lastname: Lescat
authors.forename: Claire
authors.initials: C
authors.lastname: Hoede
authors.forename: Olivier
authors.initials: O
authors.lastname: Clermont
authors.forename: Louis
authors.initials: L
authors.lastname: Garry
authors.forename: Pierre
authors.initials: P
authors.lastname: Darlu
authors.forename: Pierre
authors.initials: P
authors.lastname: Tuffery
authors.forename: Erick
authors.initials: E
authors.lastname: Denamur
authors.forename: Bertrand
authors.initials: B
authors.lastname: Picard
mesh_terms: D000115:Acetylesterase / Q000235:genetics*; D000818:Animals; D015373:Bacterial Typing Techniques; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000145:classification / Q000201:enzymology / Q000235:genetics* / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000382:microbiology; D029968:Escherichia coli Proteins / Q000235:genetics*; D005260:Female; D005816:Genetic Complementation Test; D051379:Mice; D008958:Models, Molecular; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D012697:Serine Endopeptidases / Q000235:genetics*; D014774:Virulence
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C115513:AES protein, E coli; D000115:Acetylesterase; D012697:Serine Endopeptidases; C049262:esterase B