Isolation and purification of Aeromonas sobria cytotonic enterotoxin and beta-haemolysin.

Aeromonas sp., grown in tryptone soya broth supplemented with yeast extract, 0.6%, pH 7.5, and incubated with agitation at 100 oscillations/min for 15 h at 37 degrees C produced optimal amounts of beta-haemolysin and cytotonic enterotoxin. More prolonged incubation resulted in the loss of enterotoxic activity and anion exchange chromatographic analysis indicated the presence of a moiety capable of breaking down the toxin. Anion exchange fast protein liquid chromatography resulted in a single peak of haemolytic activity and two peaks with enterotoxic activity. The cytotonic enterotoxin was purified from the fraction most active in the infant mouse assay; the second peak, which did not cross-react immunologically, may represent a second cytotonic enterotoxin. Neither peak was observed in the chromatographic fractions of filtrates from strains devoid of activity in the infant mouse assay. Purified enterotoxin, estimated to have a mol. wt of 15 kDa by SDS-PAGE, caused fluid accumulation in the infant mouse assay, was non-haemolytic to rabbit erythrocytes, caused an increase in cAMP activity in tissue culture cells and did not cross-react immunologically with components of cholera toxin or the whole toxin. Purified beta-haemolysin had an estimated mol. wt of 55 kDa, lysed rabbit erythrocytes and did not cause fluid accumulation in the infant mouse test.

Biochemical characteristics, enterotoxigenicity and susceptibility to antimicrobial agents of clinical isolates of Aeromonas species encountered in the western region of Saudi Arabia.

The biochemical characteristics, enterotoxigenicity and susceptibility to antibiotics are reported for 22 strains of Aeromonas species isolated from clinical specimens in the Western Region of Saudi Arabia. Aeromonas caviae was the species most frequently observed; a high proportion of these strains fermented lactose, whereas lactose fermentation was not observed in strains of A. hydrophila and A. sobria. Enterotoxigenicity, as judged by cytotoxicity in tissue culture was observed in three of four A. hydrophila strains and six of seven A. sobria strains, but in only one of 11 A. caviae strains. Two schemes for the biochemical assessment of enterotoxigenicity were found to be in 91% and 86% agreement respectively with cytotoxicity studies and in 95% agreement with each other. No single biochemical test correlated fully with enterotoxigenicity, but 86% of strains that oxidized gluconate produced a cytotoxin. Most strains were inhibited by concentrations of gentamicin, amikacin, chloramphenicol and tetracycline achievable in plasma. Most strains were resistant to broad-spectrum penicillins and many were also resistant to cefuroxime and cefoxitin.

Xylose absorption in Down's syndrome.

A standard xylose absorption test was carried out in 14 people with Down's syndrome (DS) and in 14 age-matched mentally deficient controls; a further 30 people with DS were similarly investigated. Mentally deficient people as a group were found to have impaired xylose absorption, the matched DS subjects having a significantly reduced xylose absorption (P less than 0.001) when compared to the mentally deficient controls. Ninety percent of the DS subjects had a xylose excretion below the normal range. At present it is not possible to identify the cause of the malabsorption but it is highly likely that the malabsorption plays a role in a number of the vitamin and mineral deficiencies found in people with DS.