Enterotoxin and cytotoxin production by Salmonella enteritidis strains isolated from gastroenteritis outbreaks

Seventy-six Salmonella enteritidis, three Salmonella virchow and one Salmonella bradenrup strains were screened for enterotoxigenicity by using the Chinese hamster ovary (CHO), Y1 adrenal, Vero and HeLa cell tests. All the strains gave positive reactions for enterotoxin production, except one, and the relative sensitivity to the toxin exhibited by the different cell lines was evaluated. An enterotoxic activity has been identified in sonicated extracts of Salm. enteritidis. This enterotoxin was purified on Agarose A-5m (Bio-Rad) and Superose 12 HR 10/30 column. The enterotoxic activity was eluted from the Superose column in the first peak. Like Vibrio cholerae toxin CT and Escherichia coli enterotoxin LT, it was blocked by GM1 ganglioside, but at a higher concentration. In addition, a cytotoxic factor has been partially identified. The procedure for isolating the cytotoxin included ammonium sulphate precipitation, size-exclusion chromatography and anion exchange chromatography. This cytotoxin factor caused inhibition of protein synthesis in cultured cells, as determined by flow cytometry and [3H]-leucine incorporation. Flow cytometry analysis also showed an activation of CHO cells when exposed to this cytotoxic factor resulting in a state of active growth. Cytotoxic activity was not blocked by gangliosides.

Murine tumorlytic factor, immunologically distinct from tumor necrosis factor-alpha and -beta, induced in the serum of mice treated with a T-cell mitogen of Corynebacterium kutscheri

Murine tumorlytic factor (TF), immunologically distinct from murine tumor necrosis factor (TNF)-alpha and -beta, was purified to a homogeneity from the serum of mice injected with a T-cell mitogen of Corynebacterium kutscheri. The treated mouse serum was purified by Lentil lectin-Sepharose chromatography, DEAE-cellulose chromatography, preparative isoelectric focusing, and high-pressure liquid chromatography to the specific activity of 1.5 x 10(6) U/mg protein. TF was 42 kDa in its oligomeric form and 14 kDa in its monomeric form. TF activity was not impaired with hamster monoclonal antibody (mAb) to recombinant murine TNF-alpha and -beta and, reciprocally, rabbit antibody to TF neutralized the bioactivity of neither murine TNF-alpha nor -beta. TF was not precipitated with the mAb to murine TNF-alpha and -beta in Western blot analysis. The partial amino acid sequence of TF was at most 33% homologous to the 46-63 sequence of mouse TNF-beta. Thus, these results suggest that TF might be a novel tumorlytic factor which is immunologically distinct from mouse TNF-alpha and -beta.

Transfer of protection to murine typhoid conferred by L-form Salmonella typhimurium in dependence of cooperation between L form-adopted macrophages and L form-induced Lyt-2+ T cells

The effector cells responsible for protection to Salmonella typhimurium in C3H/HeJ mice, conferred by L-form S. typhimurium, were determined by cell transfer test. Nonfractionated spleen cells from 6-week immune mice but not from 24-week immune animals transferred anti-S. typhimurium immunity. Treatment with anti-macrophage antiserum and complement most effectively abolished protective capacity in 6-week immune cells, while anti-T cell monoclonal antibody plus complement reduced it to a lesser extent. However, adoptive protection was achieved only by transfer of immune macrophages along with Lyt-2+ T cells selected from 6-week immune spleen cells. These Lyt-2+ T cells were cytotoxic to Kupffer cells from C3H/HeJ mice which had been infected 48 hr previously and from the mice which had been immunized 1 week previously, but not to the cells from 6-week immune mice and from normal animals. Moreover, protective capacity in immune macrophages seemed to be correlated to the degree of colonization by the L forms, and the inability to transfer immunity of 24-week immune spleen cells may be due to the decrease in the L form-colonization. These results suggest that cooperation between the L form-colonized macrophages and L form-induced cytotoxic Lyt-2+ T cells contributes to anti-S. typhimurium immunity, and might imply the immunological difference between the 6-week immune phagocytes and the cells at an early stage of infection or immunization.

Induction of hypersensitivity to endotoxin in C3H/HeJ mice by immunization with L-form Salmonella typhimurium

When endotoxin low-responder C3H/HeJ mice were immunized with L-form Salmonella typhimurium, the mice were more susceptible to a lethal challenge with S. typhimurium 1 week after immunization (1-week mice) than were the unimmunized controls. One-week immune mice produced overwhelming amounts of tumor necrosis factor-alpha (TNF-alpha) in the blood after infection, while 4-week immune mice produced lesser amounts of this cytokine with a 75% survival rate at 60 days postinfection. Pretreatment with anti-TNF-alpha antibody prevented 1-week immune mice from succumbing to acute illness. Endotoxin-stimulated peritoneal macrophages from 1-week immune mice produced higher amounts of TNF-alpha in vitro than did those from 4-week immune mice and they expressed larger amounts of TNF-alpha mRNA on Northern blot. The capacity of macrophages to produce TNF-alpha in vitro was correlated with the degree of colonization by the L form in the cells. These results suggest that the colonization by L-form S. typhimurium in macrophages alters the susceptibility to S. typhimurium of C3H/HeJ mice and that TNF-alpha might play a major role in this alteration of host resistance.