MICROBIAL SUCCESSION AND INTESTINAL ENZYME-ACTIVITIES IN THE DEVELOPING RAT

The succession of gut bacteria and selected intestinal enzyme activiti es in developing 7-35-d-old rats was studied. Aerobes and anaerobes we re identified as members of four broad major bacterial groups, i.e. Gr am-positive rods, Gram-positive cocci, Gram-negative rods and obligate anaerobes. The enzyme activities of nitro and azo reductases, beta-gl ucuronidase, dechlorinase and dehydrochlorinase were determined by ana erobic incubation of intestinal homogenates with 3,4-dichloronitrobenz ene, methyl orange, p-nitrophenyl-beta-D-glucuronide, and p,p'-DDT res pectively. Nitroreductase and azo reductase activities increased signi ficantly with the appearance of anaerobes in the large intestine. No i ncrease in either nitroreductase or azo reductase activities in the sm all intestine was found. The early and high level of beta-glucuronidas e activity in the small and large intestines coincided with high numbe rs of coliforms recovered in 7 and 14 d animals. Dehydrochlorinase act ivity appeared early but was undetectable at both 21 and 28 d. Its act ivity increased at 35 d. Dechlorinase activity was variable in develop ment. The rapid changes in the microbial flora and intestinal enzyme a ctivities may influence the susceptibility of pre-pubescent rats to a variety of toxicants. Therefore, age-dependent toxicity may be importa nt in the risk assessment of some environmental chemicals.