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Bovine and porcine enterotoxigenic and non-enterotoxigenic Escherichia coli isolates from France, Canada, and India were characterized with respect to serogroup and production of fimbrial antigens CS31A and F165. Of 231 bovine isolates from the 3 countries, 20.5% produced CS31A alone, 17.7% produced F165 alone, and 17.3% produced both CS31A and F165. On the other hand, of 84 porcine isolates from Canada, 1.2% produced CS31A alone, 14.3% produced F165 alone, and no isolate produced both CS31A and F165. CS31A was found together with F5 (K99) in 7 of 16 bovine enterotoxigenic E. coli isolates of serogroups 08, 09, 020, and 023, but was not found in any of 20 F4 (K88)- or 5 F6 (987P)-positive porcine enterotoxigenic E. coli isolates. F165 was not found in enterotoxigenic E. coli. Among non-enterotoxigenic isolates, CS31A and F165 were mainly associated with serogroups 08, 09, 011, 015, 017, 023, 025, 078, 0101, 0115, 0117, 0141, and 0153.

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The intramuscular immunization of rabbits with enterotoxin of S. weltevreden failed to provide protection against challenges with homologous Salmonella enterotoxin as well as heterologous enterotoxins (cholera toxin or E. coli LT). Similar results were obtained in rabbits immunized with cholera toxin, choleragenoid and E. coli LT. However, Salmonella antitoxin contained neutralizing antibodies against Salmonella enterotoxin (but not against cholera toxin) and thus was capable of neutralizing Salmonella enterotoxin when tested for skin permeability reaction. Immunodiffusion experiments showed that antitoxin prepared against the enterotoxin of one of the strains of S. weltevreden formed precipitin bands with enterotoxin preparations of 5 strains of S. weltevreden and 2 strains of S. anatum. However, Salmonella antitoxin failed to form precipitin bands with enterotoxins of other heterologous Salmonella species (S. dublin, S. enteritidis, S. hindmarsh and S. newport), cholera toxin and E. coli LT. The immunoelectrophoretic studies corroborated the results obtained by double immunodiffusion experiments. However, both Salmonella and cholera toxins migrated electrophoretically toward the cathode and resembled globulin in this respect. Salmonella enterotoxin, though immunogenic, yet proved unprotective through the parenteral route and appears to be antigenically distinct from cholera and E. coli enterotoxins.

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A heat-labile enterotoxin possessing both diarrheogenic and skin permeability reactions has been isolated from Salmonella weltevreden. The enterotoxin was mainly located intracellularly in the cell wall fraction. By chemical and physical techniques such as EDTA treatment of cell walls, fractional ammonium sulphate precipitation and continuous sucrose gradient centrifugation of cell sap (cell free extract) and gel filtration chromatography of culture supernatant, the enterotoxin has been partially purified. The enterotoxin resembled the heat labile enterotoxin of E. coli and the cholera toxin with respect to its thermal stability; however, it was different in its sensitivity to acidic and alkaline pH. Its activity was lost completely on treatment with Pronase and trypsin. The toxin appears to be of a high molecular weight and its enterotoxic activity is associated with a protein moiety.

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Distribution of T- and B-lymphoid cells in peripheral blood, lymph node, spleen and bone marrow of normal healthy calves and valves immunized against Theileria annulata followed by challenge on Day 50 post-immunization were studied by rosette tests. Significantly increased percentages of T- and B-lymphoid cells were recorded in immunized calves.

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Indomethacin, a rapid and intense inhibitor of prostaglandin synthesis, was used with a view to find out similarity in secretory mechanism of heat-labile enterotoxins of three diarrhoea producing enteric bacteria viz., Salmonella weltevreden, Escherichia coli and Vibrio cholerae in rabbits. A significant inhibition (90% to 94%) of biological activity of indomethacin pretreated Salmonella enterotoxin was evident in indomethacin treated rabbits, whereas the biological activity was found comparatively low (28% to 76%) in the untreated enterotoxin preparations. In contrast, the skin permeability reaction to cholera toxin remained unaltered in the absence of pretreatment of cholera toxin with indomethacin and it dropped to 55% in pre-treated toxin preparations. There was complete inhibition of biological activity of E. coli enterotoxin which did not receive indomethacin pretreatment. Based on these observations it may be inferred that indomethacin inhibits skin permeability response of heat labile enterotoxin of S. weltevreden both by blocking the effect of prostaglandins (Blocking mechanism) as well as by prostaglandin-adenyl cyclase pathway. The reduction in the biological activity of cholera toxin seems to be occurring through blocking of prostaglandins by indomethacin. In case of E. coli enterotoxin the inhibition mechanism seems operating through prostaglandin-adenyl cyclase system. These observations indicate that the Salmonella enterotoxin shares some similarity with enterotoxins of E. coli and Vibrio cholerae in respect of mechanism of action.

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A large number of enterotoxigenic strain was encountered in a group 56 Salmonella cultures belonging to 8 species viz., S. alachua, S. anatum, S. dublin, S. Enteritidis, S. hindmarsh, S. newport, S. typhimurium, S. weltevreden, and 5 serotypes of S. arizona (16:z4:--; 48:1,v:z56; 53:z52:z53; 60:r:z; 60:i:z53). These cultures were isolated mainly from humans and animals suffering from gasteroenteritis. The enterotoxigenic (diarrhoeagenic) Salmonella cultures possess capacities for both skin permeation and epithelial penetration (invasiveness). Preliminary characterization revealed that Salmonella enterotoxin is a heat-labile protein of high molecular weight. It is suggested that enterotoxigenic and invasive properties play a vital role in the pathogenesis of Salmonella diarrhoea.

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A large proportion of human and animals' (buffaloes, sheep and mares) serum samples contained haemagglutinins against a polyvalent preparation of commonly occurring Salmonella somatic groups (4, 12; 4, 5, 12; 6, 7; 9, 12; 3, 10; 11 and 16) by indirect haemagglutination test (IHA). The inhibition of Salmonella haemagglutinins in serum samples of man and animals by 2-mercaptoethanol indicated that IgM moiety of immunoglobulins mainly participated in haemagglutination. The detection of haemagglutinins in large numbers of serum samples of animals and human at a titre of 1/80 or more by IHA may be considered important from Salmonella surveillance point of view.

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Buffalo (Bos bubalis) lymphocytes were purified and tested for their E and EAC rosette forming capacity as a marker for the detection of T and B cells, respectively. Sheep erythrocytes were found to form 17.7 per cent of E rosette with buffalo lymphocytes. This population of lymphocytes is believed to be T cell. Erythrocytes of guinea-pig, rabbit, hamster, rat, chicken, dog and donkey formed a lower percentage of rosettes. Five to 18.5 per cent of SRBC-EAC rosettes were detected with buffalo lymphocytes which are believed to be B cells.

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