Invasiveness of Salmonella serotypes Typhimurium, Choleraesuis and Dublin for rabbit terminal ileum in vitro

Ten recent clinical isolates of Salmonella serotype Typhimurium from man th at were tested for their invasiveness in rabbit ileal explants in vitro, we re compared with Typhimurium strain TML, a well-characterised invasive stra in isolated from a case of human gastro-enteritis. Nine of the 10 strains s howed invasiveness that was comparable to that of strain TML, One isolate ( GM3) was apparently substantially less invasive; electron microscopy showed this strain to be histotoxic - the probable reason for its reduced recover y from ileal mucosa and thus apparent 'low' invasiveness, Salmonella seroty pe Choleraesuis strain A50, isolated from a case of systemic salmonellosis in pigs, and serotype Dublin strain 3246, isolated from a case of systemic salmonellosis in calves, were also examined. Dublin strain 3246, when grown at 37 degrees C and used immediately in the invasion assay, damaged the mu cosa in a manner similar to that of Typhimurium strain GM3, whereas Dublin strain 3246 grown at 37 degrees C and stored overnight at 4 degrees C did n ot. This was reflected in an apparently lower invasiveness of freshly grown organisms compared with that of organisms stored at 4 degrees C. In contra st, the histotoxicity of Typhimurium strain GM3 was not affected by storage at 4 degrees C. When stored at 4 degrees C, the levels of invasiveness of Choleraesuis strain A50 and Dublin strain 3246 were not significantly diffe rent from each other or from Typhimurium strain TML.