M. Gracey

DETECTION OF ENTEROTOXINS OF AEROMONAS HYDROPHILA BY A SUCKLING-MOUSE TEST

The suckling-mouse assay was reliable for detecting enterotoxigenic strains of Aeromonas hydrophila when standard conditions for growth and toxin testing were used. Enterotoxins were produced by bacteria grown in tryptone soya broth supplemented with yeast extract and aerated by shaking in an environmental incubator or water bath. When culture supernates together with dye were administered intragastrically to mice less than 6 days old, the presence of enterotoxin was assessed on the basis of a scoring system that incorporated the ratio intestinal weight: remaining body weight, and production of diarrhoea. This method should facilitate the detection of enterotoxigenic strains of Aeromonas in epidemiological studies.

Purification of cytotoxic enterotoxin of Aeromonas sobria by use of monoclonal antibodies.

Cytotoxic enterotoxin of Aeromonas sobria was purified by affinity chromatography with monoclonal antibodies. The purified enterotoxin gave a single protein band in polyacrylamide gradient gel electrophoresis and its mol. wt estimated by this technique was 63,000; it had a pI of 6.2. The purified enterotoxin caused fluid accumulation in rat ileal loops and in infant mice, was cytotoxic to cultured cells, was haemolytic to human erythrocytes, and was lethal to mice after intravenous injection. The relative concentrations of enterotoxic, cytotoxic and haemolytic activities were approximately the same in a culture filtrate and in purified, electrophoretically homogeneous enterotoxin. The three activities were also inactivated to the same extent after incubation for 10 min at 56 degrees C. There was no immunological cross-reactivity with cholera toxin (CT) nor did antiserum to CT neutralise the biological effects of the toxin.

Effects of Biliary Diversion on Intestinal Microflora in the Rat

Certain bile acids inhibit the growth in vitro of organisms commonly found in the intestine and, in particular, anaerobic bacteria. As the importance of this effect in vivo has not been demonstrated, we investigated changes in intestinal flora in the rat after diversion of bile to the urinary bladder. Five days after operation there was an increase in numbers of Proteus sp. in the stomach, mid-jejunum and caecum and of coliform bacilli in the stomach and mid-jejunum. Lacto-bacilli were increased in the stomach. There was no change in numbers of anaerobic organisms. Similar changes in bacterial flora followed 5 days of pair feeding in control rats. Our results do not suggest a specific antibacterial effect of bile salts in the rat in vivo. The changes found are probably related to semi-starvation, because the food intake of the rats after operation was about half that of control rats having an unrestricted diet.

Effects of intestinal micro-organisms on fluid and electrolyte transport in the jejunum of the rat.

Culture filtrates of micro-organisms isolated from the upper intestinal secretions of malnourished children and grown in pure culture were shown to impair the intestinal absorption of water and electrolytes in live rats. Decreased net movement out of the intestinal lumen, or actual secretion of water, sodium or potassium into the intestinal lumen, was found with culture filtrates of single isolates of Staphylococcus epidermidis, Escherichia coli 055, Escherichia coli B7A, Shigella sonnei, Klebsiella pneumoniae, Candida albicans and Candida tropicalis. These organisms have been found to contaminate upper intestinal secretions in malnourished children and it is suggested that the effects observed in these experiments might be relevant to the production of the diarrhoea that is a dominant clinical feature of childhood malnutrition.

AN EXPERIMENTAL MODEL OF GASTROINTESTINAL CANDIDIASIS

Intestinal absorption of arbutin (p-hydroxyphenyl-beta-glucoside), a non-metabolised analogue of d-glucose, and net flux of water out of the small intestinal lumen were found to be decreased in vitro in rats fed with Candida albicans. In rats on a protein-deficient diet and fed C. albicans there was net secretion of water. Sugar uptake and net water transport were also impaired in infected animals in vivo. These abnormalities were present although there was no histological evidence of invasion of the small-intestinal mucosa by C. albicans. The findings suggest that C. albicans has significant enteric pathogenicity and that this is particularly important in malnutrition.