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BMC Genomics  2006 

Complete genome sequence of Shigella flexneri 5b and comparison with Shigella flexneri 2a

DOI: 10.1186/1471-2164-7-173

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Abstract:

The Sf8401 chromosome is 4.5-Mb in size, a little smaller than that of Sf301, mainly because the former lacks the SHI-1 pathogenicity island (PAI). Compared with Sf301, there are 6 inversions and one translocation in Sf8401, which are probably mediated by insertion sequences (IS). There are clear differences in the known PAIs between these two genomes. The bacteriophage SfV segment remaining in SHI-O of Sf8401 is clearly larger than the remnants of bacteriophage SfII in Sf301. SHI-1 is absent from Sf8401 but a specific related protein is found next to the pheV locus. SHI-2 is involved in one intra-replichore inversion near the origin of replication, which may change the expression of iut/iuc genes. Moreover, genes related to the glycine-betaine biosynthesis pathway are present only in Sf8401 among the known Shigella genomes.Our data show that the two S. flexneri genomes are very similar, which suggests a high level of structural and functional conservation between the two serotypes. The differences reflect different selection pressures during evolution. The ancestor of S. flexneri probably acquired SHI-1 and SHI-2 before SHI-O was integrated and the serotypes diverged. SHI-1 was subsequently deleted from the S. flexneri 5b genome by recombination, but stabilized in the S. flexneri 2a genome. These events may have contributed to the differences in pathogenicity and epidemicity between the two serotypes of S. flexneri.Shigella species that cause bacillary dysentery or shigellosis are Gram-negative, non-sporulating, facultative anaerobes, and the disease remains a major worldwide health problem. An estimated annual infection of 160 million individuals, with 1.1 million deaths, most of them children under 5 years old in developing countries, occurs with shigellosis [1]. The poor sanitary conditions prevalent in these areas contribute to the spread of the bacteria, and the expense of antibiotics and increasing antibiotic resistance complicate treatment [2].Shigella was r

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