The relationship between nitro group reduction and the intestinal microflora.

The capacity of rats to reduce a 25-mg dose of p-nitrobenzoic acid (PNBA) was measured by quantifying the amount of this compound recovered in the urine as p-aminobenzoic acid (PABA) and its conjugates. It was found that germfree rats converted approximately 1% of PNBA to PABA; in conventional rats the conversion was approximately 25%. Various bacteria isolated from the rat cecum were selectively associated with germfree rats and it was demonstrated that these bacteria colonized their gastrointestinal tracts. In assoication with Lactobacillus plantarum, the conversion of PNBA to PABA increased to 3.9%. When these rats were further associated with Clostridium sp. and Streptoccocus faecalis, the conversion increased to approximately 12%. A general correlation was found between the capacity of constituents of the microflora to reduce PNBA in vitro and when associated with the germfree rat. Cecectomy, which removes a substantial portion of the microflora of the rat, decreases the capacity of the conventional rat to reduce PNBA. Similar experiments with p-nitrobenzenesulfonamide indicate that this compound is also largely reduced by the flora. Evidence that the reduction of the nitro group in these compounds is carried out by the intestinal microflora explains previous observations in which the reduction of these compounds in rats did not correlate with the activity of liver enzymes putative for these reactions.