Molecular and phenotypic characterization of potentially new Shigella dysenteriae serotype

From September 1997 to November 1998, the French National Center for Salmon ella and Shigella received 22 Shigella isolates recovered from 22 different patients suffering from dysentery. None of these isolates reacted with any of the antisera used to identify established Shigella serotypes, but all o f them agglutinated in the presence of antisera to a previously described p otentially new Shigella dysenteriae serotype (represented by strain 96-204) primarily isolated from stool cultures of imported diarrheal cases in Japa n. All French isolates, as well as strain 96-204, showed biochemical reacti ons typical of S. dysenteriae and gave positive results in a PCR assay for detection of the plasmid ipaH gene coding for invasiveness. No Shiga toxin gene was detected by PCR. These isolates were indistinguishable by molecula r analysis of ribosomal DNA (ribotyping) and seemed to be related to S. dys enteriae serotypes 3 and 12. However, further characterization by restricti on of the amplified O-antigen gene cluster clearly distinguished this new s erotype from all other Shigella or Escherichia coli serotypes.