Identification of enterotoxigenic Escherichia coli and serum antitoxin activity by the vascular permeability factor assay

Twenty-five strains of enterotoxigenic (tox(+)) Escherichia coli isolated in India, Bangladesh, and the U.S.A. were shown to produce vascular permeability factor (PF) activity as well as diarrheagenic activity. Sixteen strains of non-enterotoxigenic E. coli were found to be PF negative. The PF response elicited by tox(+)E. coli isolated in the U.S.A. from cases of infantile diarrhea was qualitatively different and more difficult to demonstrate. However, this problem was surmounted by assaying 25-fold concentrates of the crude enterotoxin of these strains. PF activity of various strains of tox(+)E. coli was neutralized by anti-PF antiserum prepared against the enterotoxin of strain H-10407. This anti-PF antiserum also neutralized PF activity of Vibrio cholerae enterotoxin (choleragen). Antiserum containing antibody specific for purified choleragen neutralized E. coli PF activity. These and other results indicate that the PF activity of E. coli is a function of the diarrheagenic enterotoxin as is known to be the case with choleragen. We conclude that the PF assay can be employed for the identification of tox(+)E. coli and for the detection of antitoxic antibody.

Production of vascular permeability factor by enterotoxigenic Escherichia coli isolated from man

Enterotoxin preparations derived from Escherichia coli strain H-10407 were shown to contain vascular permeability factor (PF) activity as well as diarrheagenic activity. Intradermal injection of E. coli enterotoxin (ECT) caused localized induration and permeability of small blood vessels of the skin to intravenously administered Evans blue dye. The PF assay described here demonstrated a linear dose response and was at least as sensitive as the adult rabbit ileal loop assay for detecting ECT. E. coli PF activity was heat labile and was neutralized by homologous antiserum. PF production was enhanced by the addition of yeast extract (up to 0.6%) to a Casamino Acids-salts medium. PF activity was detectable as early as 6 h in aerated (shake) cultures in the Casamino Acids-yeast extract-salts medium, pH 8.5, maximal at 18 h and essentially unchanged at 48 h. The skin test (PF) assay for ECT has numerous advantages over current assay methods which involve gastrointestinal challenge of experimental animals.

Three characteristics associated with enterotoxigenic Escherichia coli isolated from man

In Dacca, Bangladesh, potent enterotoxin-producing Escherichia coli were isolated from many hospital cases of acute cholera-like diarrhea. Enterotoxigenic (tox(+)) and non-enterotoxigenic (tox(-)) isolates of E. coli were used to investigate possible means of differentiating tox(+)E. coli from those (tox(-)) of the normal flora. The majority (81%) of the tox(+)E. coli studied were found to be negative for sucrose fermentation, 85% exhibited retarded growth in a peptone medium at pH 8.5, and 92% released large amounts of ammonium sulfate precipitable materials into culture supernatant fluids; 66.6% exhibited all three of these properties. For the tox(-) group the respective values were found to be 50%, 31%, and 34%; only 9.3% exhibited all three properties. These results indicate that it may be possible to use phenotypic characteristics other than antigenic composition and enterotoxin production for the identification of enterotoxigenic E. coli.

Blood-feeding requirements of the mosquito: geographical variation in Aedes taeniorhynchus

Wild poplulations of Aedes taeniorhynchus were polymorphic for the diets required for ovarian development. In Aedes taeniorhynchus populations from mangrove swamps, most females possessed the capacity to produce eggs on a blood-free diet. But where the grassy salt marsh was the mosquito's principal habitat,most females lacked this capacity. Both kinds of females could utiliZe a blood meal for egg production.

Differences in the response of rabbit small intestine to heat-labile and heat-stable enterotoxins of Escherichia coli

The response of adult rabbit small intestine to the heat-stable (ST) and heat-labile (LT) enterotoxins of Escherichia coli has been investigated by employing the ligated loop technique. Fluid accumulation was determined in relation to enterotoxin dose and duration of gut exposure. The individual responses to ST and LT differed in a characteristic manner. Onset of net fluid accumulation in response to ST appeared to be immediate even at the lowest dose tested. Onset of net fluid accumulation in response to LT was rapid at high doses but delayed at low doses. Maximum volume per length ratios elicited by ST occurred between 4 and 6 h after injection of loops over the entire range of doses tested. However, maximum ratios elicited by LT occurred no less than 10 h after injection even at low doses. Fluid accumulation elicited by LT increased in duration with increasing dose; high doses of LT producing a response which was sustained for at least 18 h. The net effect of these differences in reaction characteristics is a sharp increase in the proportion of the cumulative net secretory response attributable to LT with time. Therefore, a 6-h assay time is appropriate for the titration of ST, whereas an 18-h assay is not. The 18-h assay was found more appropriate for toxin-antitoxin neutralization studies since only LT was neutralized by anti-enterotoxin serum. LT of E. coli (swine) strain P-263 and (human) strain 334 was neutralized by antibody stimulated by enterotoxin from E. coli (human) strain H-10407. LT was labile to mild acid conditions, whereas ST was not.

Biochemistry of Vibrio cholerae Virulence I. Purification and Biochemical Properties of PF/Cholera Enterotoxin

A simple method for concentrating, isolating, and purifying PF/cholera enterotoxin from culture supernatant fluids is presented. Precipitation with dextran sulfate and ammonium sulfate, followed by gel filtration and ion-exchange chromatography, yielded PF/enterotoxin of high biological potency. Although not completely free from traces of vibriocidal antibody-stimulating activity, the resultant purified toxic immunogen appeared homogeneous as judged by immunoelectrophoresis, immunodiffusion, and disc electrophoresis. Advantages and disadvantages of this purification method are discussed in comparison with those of previously published techniques.

Detection of Antibody-Producing Cells of Mice Injected with Antigens of Neisseria meningitidis

The technique of Jerne et al. was adapted to the study of the antibody response of mice to Neisseria meningitidis antigens. The mice were inoculated with heated group A bacteria or antigen concentrated from their culture fluid. Sheep erythrocytes were coated with bacterial lysate or culture fluid. These antigens were shown by immune hemolysis to be group-specific and appeared to be of identical specificity. The plaque-forming cell (PFC) response obtained with either antigen was dosedependent over a range of 10 to 300 μg per mouse. However, the maximum response, reached at 4 days, was quite low. The number of PFC per 10 6 nucleated cells, elicited by the heated bacteria and culture fluid, was 15 and 7, respectively. The number of PFC declined rapidly after the peak. A second injection of heated bacteria, given 18 days after the first injection, elicited a more rapid but otherwise similar reaction, apparently involving the production of only immunoglobulin M antibodies. No hemolytic antibodies were demonstrated in the sera of these mice. The passive hemolytic plaque assay here described provided the sensitivity necessary to study the details of the antibody response of mice to meningococcal antigen.