Conventional guinea pigs provided with a solution of 5% (wt/vol) degraded carrageenan as the sole source of oral fluids developed ulcerations of their ceca and large intestines within 30 days. Similar lesions were not detected in germfree guinea pigs treated in an identical manner, suggesting that an intestinal microflora was necessary for development of intestinal lesions. To simplify the bacterial flora required for production of cecal ulcerations, 10 pools consisting of 10 bacterial strains each were isolated from the cecal microflora of carrageenan-treated animals. Groups of germfree guinea pigs were associated with 2 of the 10 pools by orogastric intubation and observed for development of disease. One-half of each group was treated with carrageenan. The two bacterial pools were characterized by the presence of cytopathic effects for WI-38 and Vero cells, increased chemotactic activity, and increased concentrations of long-chain fatty acids. The results indicated that animals associated with these two pools developed cecal ulcerations during carrageenan treatment. Preliminary results also indicated that cecal ulcerations developed in germfree animals mono-associated with a strain of Bacteroides vulgatus isolated from one of the pools, regardless of whether carrageenan was administered, suggesting a bacterial involvement in disease development in the absence of carrageenan treatment.
Because the assay of streptococcal polypeptides for nephrotoxic activity has so far depended on extensive and time-consuming rabbit experiments, alternative shorter bioassay methods were sought. Rabbit kidney cell monolayers were exposed to nephrotoxic type 12 and non-nephrotoxic type 6 streptococcal filtrates, dialysates, and polypeptides for varying periods; the latter were in doses of 1–10 mg per tube. In all cases both type 12 and type 6 products proved to be cytotoxic to the monolayers, although, in rabbits, only type 12 products were nephrotoxic. Injection of mice with similar products in varying doses and by varying routes of administration failed to distinguish between nephrotoxic and non-nephrotoxic preparations in terms of renal damage, for all preparations produced similar renal changes. It must be concluded that neither rabbit kidney cell monolayers nor mice can replace rabbits for bioassay of the nephrotoxic potency of streptococcal products.
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