Emergence of a novel Shigella flexneri serotype 4s strain that evolved from a serotype X variant in China.

This paper describes the first isolation of a new Shigella flexneri serotype, designated 4s, in Beijing, China. Genotypic and phenotypic profiling suggests that this isolate is a clone of the S. flexneri serotype X variant reference strain. Of particular concern is the multidrug resistance exhibited by this isolate.