Purification & antigenicity of Salmonella newport enterotoxin.

The enterotoxic moiety present in cell free culture supernatant (CFCS) of S. newport strains (MP/120 and BM/704) was purified and antigenically characterised. Purification was achieved to homogeneity by salt precipitation, dialysis and successive gel filtration through Sephadex G-100 and G-200 columns with the help of FPLC set. It was non-dialysable and purified enterotoxin yielded a single protein band in PAGE. It appeared to be of high molecular weight (100 KDa) and highly immunogenic in the rabbit. Antigenically, it was not related to cholera toxin, Shiga toxin or heat-labile enterotoxin of Escherichia coli.

Comparative evaluation of some bioassay models & serological tests for the detection of Salmonella enterotoxin.

Two bioassay models viz., rabbit ligated ileal loop (RLIL) and the Chinese hamster ovary (CHO) cell culture and three serological methods viz., enzyme-linked immunosorbent assay (ELISA), Biken and staphylococcal coagglutination (CoA) tests were standardized and used for the detection of Salmonella enterotoxin. A total of 37 strains belonging to 14 different serotypes of Salmonella were tested simultaneously by all the five assay models. Serological tests were standardized with antiserum against the purified enterotoxin of S. typhimurium (P/536). The CHO test was found to be the most sensitive (86.37%) followed by ELISA and CoA test (83.78%) each and Biken test (78.37%). The RLIL test was found to be least sensitive (64.86%) for detection of Salmonella enterotoxin.

Paw oedema test for detection of Salmonella enterotoxin : modification and standardization.

Paw oedema test (POT) was standardized with modifications for the detection of Salmonella enterotoxin. Instead of measuring the weight of the inoculated paws after amputating the limbs at 48 hr post-inoculation, percent relative thickness of the order of 121 +/- 3.8% at 24-48 hr was found to be a better index. This test yielded parallel results to rabbit ligated ileal loop (RLIL) technique. The test was positive with enterotoxic crude cell lysates (CL) and cell free-culture-supernatants (CFCS) of S. newport and S. typhimurium, partially purified and purified enterotoxin of S. newport and purified cholera toxin. The test was found to be specific in that non-enterotoxic CFCS did not cause significant increase in the thickness. Minimum detection level of purified S. newport enterotoxin was estimated to be as low as 20 micrograms. Thus, the modified POT was considered to be an effective and economical bioassay model for the detection of Salmonella enterotoxin.