Characterisation of virulence factors of Serratia strains isolated from foods

Out of 21 Serratia strains isolated from fresh juice and fish samples, five S. marcescens and two S. rubidaea caused lethality in mice on parenteral inoculation, but none through oral feeding. Three S. marcescens and one S. rubidaea produced heat-labile enterotoxin, detectible with the rabbit ligated ileal loop test, the mouse foot pad test and the vasopermeability factor test. Cell free culture filtrate (CFCF) of two enterotoxigenic S. mearcescens strains induced cytotoxic effect on a monolayer of Vero-cells, but CFCF of other enterotoxigenic strains could only induce cytotonic changes in Vero-cells. All strains possessed fimbriae type 3, while, only pathogenic strains had type 4 fimbriae and a colonization factor. All pathogenic Serratia strains were agglutinated at comparatively lower salt concentrations than non pathogenic strains (<- 1.3 M), and had multiple drug resistance. Their public health significance is also discussed.