Genome dynamics and diversity of Shigella species, the etiologic agents of bacillary dysentery

Abstract

The Shigella bacteria cause bacillary dysentery, which remains a significant threat to public health. The genus status and species classification appear no longer valid, as compelling evidence indicates that Shigella, as well as enteroinvasive Escherichia coli, are derived from multiple origins of E.coli and form a single pathovar. Nevertheless, Shigella dysenteriae serotype 1 causes deadly epidemics but Shigella boydii is restricted to the Indian subcontinent, while Shigella flexneri and Shigella sonnei are prevalent in developing and developed countries respectively. To begin to explain these distinctive epidemiological and pathological features at the genome level, we have carried out comparative genomics on four representative strains. Each of the Shigella genomes includes a virulence plasmid that encodes conserved primary virulence determinants. The Shigella chromosomes share most of their genes with that of E.coli K12 strain MG1655, but each has over 200 pseudogenes, 300∼700 copies of insertion sequence (IS) elements, and numerous deletions, insertions, translocations and inversions. There is extensive diversity of putative virulence genes, mostly acquired via bacteriophage-mediated lateral gene transfer. Hence, via convergent evolution involving gain and loss of functions, through bacteriophage-mediated gene acquisition, IS-mediated DNA rearrangements and formation of pseudogenes, the Shigella spp. became highly specific human pathogens with variable epidemiological and pathological features.

Salmonella Typhi: from a Human Pathogen to a Vaccine Vector

“…This is in line with other genomes of enteric bacteria sequenced so far which feature a single chromosome with 4.3-5.0 Mb in length (7)(8)(9)(10). A comparison of S. typhi isolates from around the world indicate that they are highly related and that they emerged from a single point of origin approximately 30,000 to 50,000 years ago (11).…”

Biogeography of theSulfolobus islandicuspan-genome

“…Using full-genome comparisons, other studies have similarly identified the parallel presence of variable genes in microbial populations that appear differentiated. This has led to the conclusion that the variable gene pool is unbounded, sampled freely by individuals, and incorporated where genes are advantageous (9,(27)(28)(29)(30).…”

“…These studies found a rapid flux of genes through genomes, some of which can be associated with parallel adaptive gene gain by divergent strains (5,9,10,28,35,36). Gene loss has also been recognized as an important force in genome variation, especially in host-associated microbial populations (37)(38)(39)(40).…”

“…Gene loss has also been recognized as an important force in genome variation, especially in host-associated microbial populations (37)(38)(39)(40). In particular, several derived pathogens, Salmonella enterica Typhi (32,36) and Shigella (28), and intracellular symbionts, Buchnera (41,42), have been suggested to undergo significant genome reductions. Gene loss has also been identified in free-living microorganisms (43), and it is often assumed that loss is mechanistically simpler than gain when modeling genome evolution (9,33,44,45), although the relative importance of gene gain and loss to variation in the pan-genome is still the subject of debate.…”

Antibiogram Pattern of Shigella flexneri: Effect of Bio Field Treatment

“…The key characteristic feature for S. flexneri bacterium is non-lactose fermenting, but it can ferment glucose with production of acid [2].…”