Invasive ability of Plesiomonas shigelloides.

Five of 16 strains of Plesiomonas shigelloides freshly isolated from children with acute diarrhoea, exhibited invasiveness for HeLa cells comparable to that of Shigella sonnei. None of the five, however, gave a positive reaction in the Sereny test. Although three of the invasive strains shared antigens with Shigella, no correlation was observed between invasiveness and the possession of such antigens. Only one of the invasive strains produced a toxin detectable as causing rounding of HeLa cells, although others released a product which inhibited protein synthesis in HeLa cells but which failed to provoke any dramatic morphological change.