[Shigella flexneri strains having a new type antigen 89-141].

Two Shigella strains (89-141 and 89-11) isolated from the stool of patients returning from abroad (both from India) in Tokyo in 1989 showed an atypical serologic reaction of agglutination with only polyvalent antiserum to S. flexneri prepared commercially. These strains had the typical biochemical characteristics of S. flexneri and were biochemically identical. Both strains were positive for Serény test in guinea pig eye and cell-invasion test in HeLa cells. The strains also had virulence-plasmid encoding outer membrane proteins, indicating pathogenicity. The results of antigenic analyses showed that the strains were serologically identical to each other and gave significant cross-reactions with S. flexneri variant Y that has only group 3, 4 factor antigen. However, the results of reciprocal absorption tests showed that the O antigen of these strains was not identical to S. flexneri variant Y, and they were confirmed to have an additional type-specific antigen which is not included among the known S. flexneri type antigen I-VI or provisional type 88-893 which were proposed by us in 1992. Furthermore, one stock strain (TSH508) formally identified as S. flexneri variant X has this type antigen, suggesting that the new antigen can be classified into two subtypes by combination of group factor antigen. Strain 89-141 is designated as the test strain for this new type antigen of S. flexneri.