Abstract
BackgroundShigella flexneri is the major cause of shigellosis in the developing countries. The O-antigen component of the lipopolysaccharide is one of the key virulence determinants required for the pathogenesis of S. flexneri. The glucosyltransferase and/or acetyltransferase genes responsible for the modification of the O-antigen are encoded by temperate serotype converting bacteriophage present in the S. flexneri genome. Several serotype converting phages have previously been isolated and characterized, however, attempts to isolate a serotype converting phage which encodes the modification genes of serotypes 4a strain have not been successful.ResultsIn this study, a novel temperate serotype converting bacteriophage SfIV was isolated. Lysogenisation of phage SfIV converted serotype Y strain to serotype 4a. Electron microscopy indicated that SfIV belongs to Myoviridae family. The 39,758 bp genome of phage SfIV encompasses 54 open reading frames (orfs). Protein level comparison of SfIV with other serotype converting phages of S. flexneri revealed that SfIV is similar to phage SfII and SfV. The comparative analysis also revealed that SfIV phage contained five proteins which were not found in any other phages of S. flexneri. These proteins were: a tail fiber assembly protein, two hypothetical proteins with no clear function, and two other unknown proteins which were encoded by orfs present on a moron, that presumably got introduced in SfIV genome from another species via a transposon. These unique proteins of SfIV may play a role in the pathogenesis of the host.ConclusionsThis study reports the isolation and complete genome sequence analysis of bacteriophage SfIV. The SfIV phage has a host range significantly different from the other phages of Shigella. Comparative genome analysis identified several proteins unique to SfIV, which may potentially be involved in the survival and pathogenesis of its host. These findings will further our understanding on the evolution of these phages, and will also facilitate studies on development of new phage vectors and therapeutic agents to control infections caused by S. flexneri.
Highlights
Shigella flexneri is the major cause of shigellosis in the developing countries
Phage and media Bacteriophage SfIV was isolated from S. flexneri 4av strain (SFL1522, International Centre for Diarrhoeal Disease Research, Bangladesh) using the UV irradiation protocol described by Adams et al [8]
Isolation of bacteriophage SfIV SfIV phage was induced from serotype 4av, strain SFL1522
Summary
Shigella flexneri is the major cause of shigellosis in the developing countries. The glucosyltransferase and/or acetyltransferase genes responsible for the modification of the O-antigen are encoded by temperate serotype converting bacteriophage present in the S. flexneri genome. Modifications to the basic O-antigen backbone, which occur through glucosylation and/or O-acetylation of one or more sugars within the repeating unit, form the basis of serotype conversion. The genes which mediate the addition of glucosyl or O-acetyl residues to the specific sugars are encoded by temperate bacteriophage. These phage are integrated into the host chromosome, forming a prophage that stably expresses serotype conversion genes [7]
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