Enteropathogenicity of Plesiomonas shigelloides

Abstract

Live cultures of 13 strains of Plesiomonas shigelloides isolated from different sources caused accumulation of fluid in rabbit ileal loops in the range 1-2 ml/cm of gut. Some strains required one or two passages in ileal loops before they gave a positive reaction. Inocula multiplied by c. 104-fold in the loops within the 6 h of the experiment. Maximal fluid accumulation was obtained with an inoculum of 104-105 colony-forming units. Culture filtrates, in volumes of 0.25 ml, also caused fluid accumulation comparable with that caused by live cells. The fluid accumulation started within 1-2 h, and showed a marked increase up to 4 h, with no appreciable change by 6-8 h, and a slight increase at 18 h. Heat treatment at 121°C for 10 min. did not affect the ability of filtrates to cause fluid accumulation. Suckling-mouse assay was positive for all the strains tested. The culture filtrates caused dislodgement of Chinese hamster ovarian and mouse adrenal tissue-culture cells from plate surfaces, or lysis of the cells. None of the strains caused keratoconjunctivitis in rabbit or guinea-pig eyes, and bacteria were not seen inside the epithelial cells of HeLa tissue cultures. The results of the investigation indicate the production of a heat-stable enterotoxin by P. shigelloides, while the elaboration of a heat-labile enterotoxin cannot be excluded. They do not suggest invasiveness. They give experimental support for an aetiological role for P. shigelloides in the production of diarrhoea, as has been previously suggested by epidemiological evidence.