CHARACTERIZATION OF PLESIOMONAS-SHIGELLOIDES STRAINS THAT SHARE TYPE-SPECIFIC ANTIGEN WITH SHIGELLA-FLEXNERI-6 AND COMMON GROUP-1 ANTIGEN WITH SHIGELLA-FLEXNERI SPP AND SHIGELLA-DYSENTERIAE-1

Three strains of Plesiomonas shigelloides isolated from patients with diarrhoea were agglutinated with Shigella flexneri 6 antiserum in slid e and tube tests. All the strains were also agglutinated with a monocl onal antibody to the common group 1 antigen shared between S.flexneri serotypes and S. dysenteriae type 1. Further studies with one strain a lso showed sharing of antigenicity in an enzyme-linked immunosorbent a ssay. The results suggest that the strains share type-specific antigen with S. flexneri 6 and the common group 1 antigen with S. flexneri se rotypes and S. dysenteriae 1. The sharing of antigens may have implica tions for cross-protection. One strain adhered to HEp-2 cell monolayer s. None of the strains contained high mol. wt plasmids and there was n o sequence homology with the invasiveness plasmid of Shigella spp. in DNA probe hybridisation. They were susceptible to the commonly used an tibiotics. However, they possessed four other virulence-associated pro perties of Shigella spp. that included Congo-red binding, hydrophobici ty, toxicity to HeLa cells and HEp-2 cell invasiveness (although they gave negative results in the Sereny test for invasiveness). These data suggest that the three unique strains might be considered pathogenic. Studies in animal models and human volunteers would be necessary to e stablish their pathogenic potential.