Clonal relationships among Shigella serotypes suggested by cryptic flagellin gene polymorphism

Area of Science:

• Microbiology
• Genetics
• Bacterial Taxonomy

Background:

• Shigella species are major causes of bacterial dysentery.
• Accurate identification and differentiation of Shigella strains are crucial for public health.
• The fliC gene, encoding the flagellin protein, is a key target for bacterial typing.

Purpose of the Study:

• To investigate the presence and diversity of cryptic fliC alleles across Shigella species.
• To develop a molecular method for differentiating Shigella strains based on fliC gene variations.
• To explore the evolutionary relationship between Shigella and Escherichia coli.

Main Methods:

• Genomic DNA extraction from 120 Shigella strains representing four species.
• PCR amplification of the fliC gene.
• Restriction fragment length polymorphism (RFLP) analysis using HhaI endonuclease.
• Clustering of patterns to define F types.

Main Results:

• Generated 17 distinct fliC HhaI fragment patterns (F types) from 120 Shigella strains.
• Unique patterns were observed for several Shigella dysenteriae and Shigella boydii serotypes.
• Some serotypes, like Shigella dysenteriae serotype 13 and Shigella sonnei biotype e, showed heterogeneity with multiple F types.
• S. flexneri serotypes exhibited distinct clustering patterns.
• No overlap was found between Shigella fliC patterns and previously described Escherichia coli fliC patterns.

Conclusions:

• The fliC RFLP method effectively differentiates Shigella strains and serotypes.
• The findings support the hypothesis that Shigella evolved from diverse Escherichia coli ancestors.
• This molecular approach is a valuable tool for identifying clinically significant Shigella isolates and confirming atypical strains.