Revisiting the Molecular Evolutionary History of Shigella spp.

Abstract

The theory that Shigella is derived from multiple independent origins of Escherichia coli (Pupo et al. 2000) has been challenged by recent findings that the virulence plasmids (VPs) and the chromosomes share a similar evolutionary history (Escobar-Paramo et al. 2003), which suggests that an ancestral VP entered an E. coli strain only once, which gave rise to Shigella spp. In an attempt to resolve these conflicting theories, we constructed three phylogenetic trees in this study: a robust chromosomal tree using 23 housekeeping genes from 46 strains of Shigella and enteroinvasive E. coli (EIEC), a chromosomal tree using 4 housekeeping genes from 19 EcoR strains and 46 Shigella/EIEC strains, and a VP tree using 5 genes outside of the VP cell-entry region from 38 Shigella/EIEC strains. Both chromosomal trees group Shigella into three main clusters and five outliers, and strongly suggest that Shigella has multiple origins within E. coli. Most strikingly, the VP tree shows that the VPs from two main Shigella clusters, C1 and C2, are more closely related, which contradicts the chromosomal trees that place C2 and C3 next to each other but C1 at a distance. Additionally, we have identified a complete tra operon of the F-plasmid in the genome sequence of an EIEC strain and found that two other EIEC strains are also likely to possess a complete tra operon. All lines of evidence support an alternative multiorigin theory that transferable diverse ancestral VPs entered diverse origins of E. coli multiple times during a prolonged period of time, resulting in Shigella species with diverse genomes but similar pathogenic properties.

Infection strategies of enteric pathogenic Escherichia coli

“…30,31 EIEC and Shigella can be distinguished by minor biochemical tests but in general have the same virulence mechanisms and disease symptoms. Strains of EIEC and Shigella appear to have evolved independently to share many characteristics, 32 and EIEC strains seen today may simply be intermediates between E. coli and Shigella. We therefore direct the reader to the excellent review on Shigella species contained in this issue for in depth analysis of this pathotype.…”

Selection and Validation of a Multilocus Variable-Number Tandem-Repeat Analysis Panel for Typing Shigella spp

“…In the United States, PulseNet, a network of laboratories implicated in foodborne disease surveillance (42), uses PFGE typing coupled with strict quality control procedures in order to ensure interlaboratory reproducibility, but this approach remains laborintensive for routine clinical strain typing, so cheaper alternatives are actively being pursued. Multilocus sequence typing (MLST) is a very powerful approach, and it provides a clear view of the population structure (52). However, it is not yet appropriate for the routine, first-line genotyping of a large number of isolates.…”

Escherichiacoli DERIVED FROM DIFFERENT SOURCES SHARE ANTIGENIC CHARACTERISTICS WITH Shigellaboydii 18AND VIRULENCE FACTORS WITH ENTEROTOXIGENIC E. coli

“…Res. 4(10), 629-638 630 species are closely related to enteroinvasive E. coli (EIEC), which suggests that distinct ancestral lineages of E. coli gave rise to EIEC and Shigella through a process of convergent evolution by acquiring of similar pathogenic characteristics (Pupo, 2000;Peng, 2006;Yang, 2007;Peng, 2009). According to a study based on analyzing housekeeping genes, both genera constitute one single pathotype of E. coli (Lan, 2004).…”