Intestinal Bacteria and Disease

A substance producing cytotoxicity in tissue culture was detected in stool specimens from all of four patients with pseudomembranous colitis due to antibiotics and in one of 54 with antibiotic-associated diarrhea. These stools also caused enterocolitis when injected intracecally into hamsters. On each occasion, cytotoxicity in tissue culture and enterocolitis in hamsters were neutralized by pretreatment with gas-gangrene antitoxin. The toxicity in both tissue cultures and hamsters could be reproduced with broth cultures of clostridia strains isolated from four of the five stools. These results suggest that toxin-producing clostridia are responsible for antibiotic-associated pseudomembranous colitis.

A plate assay was developed for the detection of anaerobic bacteria that produce azoreductases. With this plate assay, 10 strains of anaerobic bacteria capable of reducing azo dyes were isolated from human feces and identified as Eubacterium hadrum (2 strains), Eubacterium spp. (2 species), Clostridium clostridiiforme, a Butyrivibrio sp., a Bacteroides sp., Clostridium paraputrificum, Clostridium nexile, and a Clostridium sp. The average rate of reduction of Direct Blue 15 dye (a dimethoxybenzidine-based dye) in these strains ranged from 16 to 135 nmol of dye per min per mg of protein. The enzymes were inactivated by oxygen. In seven isolates, a flavin compound (riboflavin, flavin adenine dinucleotide, or flavin mononucleotide) was required for azoreductase activity. In the other three isolates and in Clostridium perfringens, no added flavin was required for activity. Nondenaturing polyacrylamide gel electrophoresis showed that each bacterium expressed only one azoreductase isozyme. At least three types of azoreductase enzyme were produced by the different isolates. All of the azoreductases were produced constitutively and released extracellularly.