Comparison of assay of coliform enterotoxins by conventional techniques versus in vivo intestinal perfusion

Enterotoxic activity of Klebsiella oxytoca cytotoxin in rabbit intestinal loops

We examined the enterotoxicity of a Klebsiella oxytoca cytotoxin which is produced by K. oxytoca OK-1, a strain from a patient with antibiotic-associated hemorrhagic colitis. Injection of the cytotoxin into ligated ileal and colonic loops in rabbits caused the accumulation of fluid in the loops. The fluid was bloody in the ileal loops but not in the colonic ones. Histological examination revealed intense mucosal hemorrhage with erosion in the ileum, whereas no microscopic change was noted in the colon. The fluid accumulation was shown to be a dose-dependent response in both ileal and colonic loops. The amounts of the cytotoxin required for maximal fluid accumulation in ileal and colonic loops were 60 and 10 micrograms, respectively. Fluid accumulation was first noticeable in ileal loops 12 h and in colonic ones 5 h after the injection of these doses of the cytotoxin and then proceeded with time. When K. oxytoca OK-1, a cytotoxin-producing strain, was inoculated into the loops at doses of 1 x 10(8) and 5 x 10(9) CFU, similar fluid accumulation was observed. However, inoculation of K. oxytoca ATCC 13182, a non-cytotoxin-producing strain, at the same doses did not cause any change. These results suggest that the cytotoxin-producing strain of K. oxytoca is the causative organism of antibiotic-associated hemorrhagic colitis and that the toxin is the factor responsible for pathogenesis.

Role of bacterial toxins, bile acids, and free fatty acids in colonic water malabsorption in tropical sprue

Colonic perfusion studies in 10 southern Indian patients with tropical sprue and nine matched healthy adults revealed a defect of water and sodium absorption from the colon in sprue. Heat-labile and heat-stable enterotoxin production was not detected in coliforms cultured from the feces of any of the 19 subjects. The 24-hr fecal bile acid output was increased in patients with sprue, but fecal aqueous bile acid concentrations remained within normal limits, and these did not correlate with defects in colonic water and sodium absorption. Fecal free fatty acid excretion was markedly increased in sprue. There was a negative correlation between fecal excretion of unsaturated free fatty acids and colonic water and sodium absorption.

Enteropathogenicity of Klebsiella pneumoniae strains isolated from stools of diarrhoeal patients and other clinical specimens: an experimental study

In recent years strains of Klebsiella pneumoniae have been implicated as intestinal pathogen. Sixty three strains isolated from faeces of children with or without diarrhoea and other specimens of extraintestinal infections were tested for their enteropathogenicity in biological models. Thirty nine of them isolated from different sources caused accumulation of fluid in rabbit ileal loops comparable to that caused by toxigenic V. cholerae 569B. Ten strains, however, required 1-3 serial passages in rabbit gut before giving a positive loop reaction. Culture filtrates of these 39 strains also caused fluid accumulation comparable to that caused by live cells indicating elaboration of enterotoxic substance(s) in the medium. The enterotoxic factor was found to be heat-stable. However, the pattern of time course of fluid accumulation in ileal loops indicated elaboration of an additional heat labile factor. Most of the strains produced cytoxic factor as well. The mode of action of the toxin/s in secretion of fluid in experimental model possibly involve cAMP and prostaglandin. However, further studies are necessary to elucidate the exact mode of action of the enterotoxins. None of the strains tested was found to be enteroinvasive.

Immunological properties of purified Klebsiella pneumoniae heat-stable enterotoxin

Klebsiella pneumoniae heat-stable enterotoxin was purified to apparent homogenicity by the same techniques used to purify Escherichia coli heat-stable enterotoxin. The two toxins had the same potency in the suckling mouse assay and showed immunological cross-reactivity in enzyme-linked immunosorbent assay, neutralization of secretory activity by specific hyperimmune antisera, and protection against active challenge in rats immunized with a vaccine containing synthetically produced E. coli heat-stable enterotoxin.

Cultural methods for the production of heat-stable enterotoxin by porcine strains of Escherichia coli and its detection by the infant mouse test

Casamino acids-yeast extract medium (CAY) and a tryptone-yeast extract medium (TY-1) were evaluated in testing for production of heat-stable enterotoxin (ST) by porcine strains of Escherichia coli using the infant mouse assay. More strains were ST-positive when grown in CAY medium than in TY-1 medium. Questionably or indeterminately ST positive strains were investigated in detail to determine whether or not they were weak ST producers. Growth in four different media and in different batches of CAY medium, inactivation of culture supernatant fluids at a lower temperature, addition of mitomycin C to growing cultures and preparation of periplasm-cytoplasm fractions of bacteria by sonication, all failed to yield ST positive samples. ST value limits (i.e. ratios of intestinal weight to remaining body weight of challenged mice), which clearly differentiated positive or negative strains for ST production, were set for CAY medium. A minimal salts-amino acids medium (MSA) was devised. Both in shake flask and fermenter cultures MSA medium gave better ST yields than CAY and a previously described defined medium.

Probing for enterotoxigenicity among the salmonellae: an evaluation of biological assays

Sixty-eight Salmonella strains representing 39 serotypes were variously screened for enterotoxigenicity by using the Chinese hamster ovary (CHO), Y1 adrenal, and Vero cell tests, rabbit skin tests for delayed permeabiltity factor (DPF) and rapid permeability factor (RPF), the rabbit ileal loop test, and the infant mouse test. An iron-sufficient medium, YT-1, and a deferrated medium, DF, were compared. Of the culture supernatant fluids of strains grown in DF medium, 66% yielded positive reactions in the CHO cell test compared with only 10% with TY-1 medium. The corresponding performances with supernatant fluids of DF medium cultures in Y1 adrenal and Vero cell tests were 85 and 69% positive, respectively. The overall agreement between the Y1 adrenal or CHO cell test and the rabbit skin test for DPF, i.e., positive or negative in both tests, was about 70%. Positivity in DPF tests was a better predictor of positivity in either the Y1 adrenal or rabbit ileal loop test than vice versa. CHO cell, DPF, and rabbit ileal loop reactivities of unheated culture filtrates were each neutralized by anticholera antitoxin. Only four strains gave positive reactions in the infant mouse test, whereas up to 66% were positive for RPF in rabbit skin, based on positivity in Ty-1 or DR medium or both. DPF and RPF were produced by 35% of the strains. Of the 28 isolates from human stools, 82 and 92% and all of 11 strains tested were positive in the DPF, Y1 adrenal cell, and rabbit ileal loop tests, respectively. The corresponding data for 17 sewage isolates, representing 17 different serotypes rarely isolated from human stools in Sweden, were 63 and 69% and 8 of 8 tested. On the basis of this investigation, rabbit skin tests for both DPF and RPF provide the most reliable means of screening for enterotoxigenicity among salmonellae.

Enterotoxins from gram-negative bacteria relevant for veterinary medicine

The chemistry, mechanism of action, assay methods, pharmacology, and prevention and treatment of diarrhoea due to toxins of gram-negative microbes are discussed. Other virulence factors are mentioned briefly. Special emphasis is placed on non-specific treatment by oral rehydration.