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Open Access Research article

Genesis of a novel Shigella flexneri serotype by sequential infection of serotype-converting bacteriophages SfX and SfI

Qiangzheng Sun1, Ruiting Lan2, Yiting Wang1, Jianping Wang1, Xia Luo1, Shaomin Zhang1, Peijing Li1, Yan Wang1, Changyun Ye1, Huaiqi Jing1 and Jianguo Xu1*

Author Affiliations

1 State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, China CDC, P.O. Box 5, Changping, Beijing, China

2 School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia

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BMC Microbiology 2011, 11:269  doi:10.1186/1471-2180-11-269

Published: 30 December 2011

Abstract

Background

Shigella flexneri is the major pathogen causing bacillary dysentery. Fifteen serotypes have been recognized up to now. The genesis of new S. flexneri serotypes is commonly mediated by serotype-converting bacteriophages. Untypeable or novel serotypes from natural infections had been reported worldwide but have not been generated in laboratory.

Results

A new S. flexneri serotype-serotype 1 d was generated when a S. flexneri serotype Y strain (native LPS) was sequentially infected with 2 serotype-converting bacteriophages, SfX first and then SfI. The new serotype 1 d strain agglutinated with both serotype X-specific anti-7;8 grouping serum and serotype 1a-specific anti- I typing serum, and differed from subserotypes 1a, 1b and 1c. Twenty four S. flexneri clinical isolates of serotype X were all converted to serotype 1 d by infection with phage SfI. PCR and sequencing revealed that SfI and SfX were integrated in tandem into the proA-yaiC region of the host chromosome.

Conclusions

These findings suggest a new S. flexneri serotype could be created in nature. Such a conversion may be constrained by susceptibility of a strain to infection by a given serotype-converting bacteriophage. This finding has significant implications in the emergence of new S. flexneri serotypes in nature.