Rapid detection of a new cell-associated Salmonella cytotonic enterotoxin in cell sonicates by Chinese hamster ovary cells

Current perspectives in salmonellosis

Salmonellosis remains an important human and animal problem worldwide and, despite extensive research effort, many of the details of its pathogenesis are not known. While there have been recent advances in some aspects of pathogenesis, other areas are not understood. The host adaptation shown by several serotypes and the recent dramatic changes in the predominance of particular serotypes are examples. Molecular techniques using in vitro model systems have identified several genes involved in adhesion and invasion, though their function and even their relevance to disease remain poorly defined. Similarly, several potential toxins have been identified and the genes cloned, although their significance is far from clear. Some of the essential genes on the large virulence plasmids have been defined, and these are known to be necessary for the establishment of systemic infection. Two of these genes are regulatory, but the function of the other genes is unknown. A general theme has been the identification of gene systems involved in regulation of virulence. New vaccines, based on 'rational attenuation' are being designed, and these have also been used to carry heterologous antigens; such vaccines are currently undergoing trials. The improved understanding of the pathogenesis of salmonellosis may also provide a model of wide applicability to a more general understanding of bacterial pathogenesis. New techniques, including the polymerase chain reaction, are being applied to diagnose salmonellosis.

Toxin profiles, and cell-surface properties of Salmonella strains isolated from Swedish travelers

Toxin production, cell-surface hydrophobicity and fibronectin-binding properties of 21 Salmonella strains of different species, isolated from Swedish travelers to different parts of the world, were studied. Cell sonicate supernatants from blood agar grown cultures of 80% of the strains induced rabbit skin permeability reaction in the form of induration and/or blueing while 33% of the strains also produced cell necrotizing factor on rabbit skin. Four strains were negative in the rabbit skin permeability test, while only two were negative when tested on CHO cells. When cultured on blood agar, a majority of the strains (17/21) showed low cell-surface hydrophobicity, showing no aggregation even at 1.5 M ammonium sulfate concentration in salt aggregation test (SAT), while only four strains showed high cell-surface hydrophobicity. Furthermore, these strains could be classified as low fibronectin binders due to their poor interaction with fibronectin or its 29 kDa N-terminal fragment.

Growth conditions for the expression of fibronectin and collagen binding to Salmonella

Binding of 125I-fibronectin, its 125I-labelled 29-kDa aminoterminal fragment, and 125I-collagen to cells of 13 Salmonella strains grown in broth and agar media at three different temperatures was studied. Of the 13 strains, 7 had only smooth colony morphologies while three strains were pairs of both smooth strains and their corresponding rough variants. The three rough variants showed higher binding to fibronectin, it's 29-kDa fragment and to collagen, than the corresponding smooth forms. However, the percentage of 125I-protein bound was greatly influenced by the growth conditions. In these three pairs of strains, there was a direct correlation between cell-surface hydrophobicity and the binding activity, but this correlation was not observed in the remaining strains. Thus, some of the strains showed high cell-surface hydrophobicity but low binding activity under optimal growth conditions. The highest binding rates of fibronectin and of it's 29-kDA fragment were obtained with bacteria grown on colonisation factor antigen (CFA) agar at 33 degrees C, while the binding to collagen was slightly higher when bacteria were cultured on tryptic soy agar.

Detection of Shiga-like (SL) toxins of enteropathogenic Escherichia coli (EPEC) of human, porcine, calf, and lamb origin on Vero and HeLa S3 cells: a comparative study

One hundred and forty eight strains of human, porcine, calf and lamb origin belonging to different enteropathogenic O:H serotypes isolated in 13 countries in four continents were tested for production of Shiga, Shiga-like (SL) and other cytotoxins on Vero cells and HeLa (S3 subline) cells in tissue cultures. Altogether, 45% human strains and 89% porcine strains were defined as strong toxin producers (toxin titre greater than or equal to 1:100) on Vero or HeLa S3 cells while 31% of human and 9% porcine strains were regarded as moderate to weak toxin producers (toxin titre less than 1:100). Twenty three percent of human and 1.5% of porcine strains were negative for Shiga or SL-toxin. Polymyxin release of Shiga or SL toxins from bacterial colonies of blood agar grown cultures is recommended as it is simple and effective method facilitating the detection of even low levels of toxins in EPEC or non-EPEC strains. Of the ten strains from calves and lambs, only four were strong toxin producers when cell-free culture supernatants were tested while a polymyxin release method showed that 8 strains were strong toxin producers. One strain was negative by both methods. The high proportion of Shiga/SL toxin negative strains in all O:H serotypes of human origin (but not of porcine origin, especially O 139 serogroup) suggests that systematic studies should continue to look for new toxins in freshly isolated strains grown under in vivo like conditions, e.g. in iron depleted culture media.

Toxins, putative cell adhesins and fibronectin binding properties of Salmonella dublin

Fifty Salmonella dublin strains isolated from cattle and human diarrhoeal cases were assayed for toxin production, haemagglutination, cell-surface hydrophobicity and fibronectin-binding properties. Most strains (65% of tested) produced cytotonic toxins and cytotoxic factors when tested on Chinese hamster ovary (CHO) cells and rabbit skin test. However, only three strains produced a skin-permeability factor as determined in pig skin intra-dermal tests. None of the strains were positive in pig intestinal loop tests. Six of the 32 strains tested for 125I-fibronectin and its 125I-29 kDa N-terminal domain binding showed 10-17% and 6-10% binding, respectively. Most of the strains expressed mannose-sensitive haemagglutination (MSHA) (76%) and high cell-surface hydrophobicity (74%) when grown at 37 degrees C. At 20 degrees C the expression of MSHA and especially the expression of high cell-surface hydrophobicity were reduced. Twelve strains grown at 37 degrees C did not haemagglutinate erythrocytes from five animal species used in this study, while six of these strains expressed high cell-surface hydrophobicity. Salmonella dublin strains isolated in Denmark appeared to express a higher frequency of fimbriae type 1 (MSHA) and a lower frequency of high cell-surface hydrophobicity than the strains from external sources.

Enterotoxigenicity among Salmonella typhimurium strains isolated in France

Twenty strains of Salmonella typhimurium isolated in France from patients with diarrhea were tested for enterotoxins and cytotoxic factors by conventional bioassays. Eighteen of the strains produced enterotoxins to varying degrees and did not react with antisera to Escherichia coli heat-labile enterotoxin. Cytotoxic factors were present in two strains. These findings suggest that efforts to elucidate the virulence mechanisms of Salmonella spp. isolated in different parts of the world should be renewed.