Abstract
Because presence of nitrite in the intestines of animals can be a risk factor of carcinogenesis, nitrate and nitrite reduction by the intestinal microbes of dogs and cats was examined by using fecal samples. Incubation of dog and cat feces with nitrate indicated that all the animals examined had nitrate- and nitrite-reducing bacteria in their intestines. The ratio of nitrite reduction rate to nitr ate reduction rate was found to decrease with the ages of dogs and cats, suggesting that nitrite can be accumulated in senior animals. Nitrite reductase activity in mixed fecal microbes increased with an increase in nitrite concentration in the medium, suggesting that the synthesis of nitrite reductase is enhanced by nitrite. The optimal pH of nitrate and nitrite reduction by mixed fecal microbes was 7.0, and in a pH range of 6.0-7.2 nitrate reduction was faster than nitrite reduction, suggesting that nitrite can be accumulated within this pH range. Because nitrate reduction rate was low at a pH value below 6.0, it is desirable to keep the pH of large intestines around 6.0. When formate was added as an electron donor to cultures of mixed fecal microbes, the ratio of nitrite reduction rate to nitrate reduction rate was enhanced, suggesting that nitrite accumulation in the intestines can be prevented by increasing formate production by intestinal bacteria.
