Quantitative studies of invasion of rabbit ileal mucosa by Salmonella typhimurium strains which differ in virulence in a model of gastroenteritis.

An asymmetric organ culture system in which ileal tissues, freshly removed from rabbits, can be maintained structurally and functionally for up to 4 h has been developed. The composition of the solutions used to maintain ileal tissue in vitro were as follows. The serosal surface was bathed in the World Health Organization (WHO) rehydration formulation: NaCl, 60 mM; NaHCO3, 30 mM; KCl, 20 mM; and glucose, 111 mM. The mucosal surface was bathed in the same solution with two important changes: all the sodium was replaced by choline, which is not absorbed, and tissue culture medium (consisting of commercial minimal essential medium to which was added fetal calf serum and glutamine to final concentrations of 10% [vol/vol] and 2.0 mM, respectively) was added to the choline-containing medium to a final concentration of 10% (vol/vol). The initial invasiveness (first 2 h) of seven strains of Salmonella typhimurium differing in virulence (defined in terms of clinical origin or the ability to induce fluid loss in monkeys or rabbit ileal loops) was assessed quantitatively in an in vitro invasion assay with the organ culture system. The virulent strains (TML, W118, and WAKE) were found to be about 25- to 100-fold more invasive than the avirulent strains (SL1027, M206, LT7, and Thax-1). Thus, a clear correlation between initial mucosal invasion and virulence of S. typhimurium in a model which is relevant to human gastroenteritis was established. This is the first time, to our knowledge, that quantitative studies of invasiveness have been carried out in vitro on freshly isolated functioning gut.