PLATES XIII-XVIT is now generally accepted that strains of Staphylococcus aureus isolated from patients with staphylococcal toxic epidermal necrolysis of Ritter's type (TEN) or staphylococcal bullous impetigo produce an exotoxin, termed epidermolytic toxin, that is responsible for the intra-epidermal splitting in the plane of the stratum granulosum that characterises these lesions. In TEN, large areas of skin are affected and the loosened epidermis peels extensively. The discovery of epidermolytic toxin followed the important observation of Melish and Glasgow (1970) that staphylococci isolated from patients with TEN or bullous impetigo caused extensive epidermal splitting when injected into newborn mice. Subsequent work has been concerned mainly with the isolation and partial characterisation of the epidermolytic toxin (Arbuthnott et al. The toxin is a relatively thermostable antigenic protein with a molecular weight of approximately 25 000. The preparative isoelectric focusing studies of Arbuthnott et al. (1974) showed that the main form of epidermolytic toxin has PI = 7.0; a minor component having a PI = 6-0 was detected. In thinlayer-gel isoelectric focusing the main form exhibited complex microheterogeneity, and up to seven protein bands were detected between pH 6-2 and 7.0. Recently, Japanese workers have described the isolation of two serologically distinct forms termed A and B toxins (Kondo et al., 1974 and 1975), and the studies of Arbuthnott et al. (1974) also suggested the existence of two antigenically distinct forms of the toxin.The present study was undertaken with the aim of assessing the specificity and sensitivity of in-vitro methods for detecting and measuring epidermolytic toxin production by S. aureus. The strains were provided by Dr Elizabeth H.

The ability of certain lipids to induce polymerization of staphylococcal a-toxin has been investigated using polyacrylamide disc gel electrophoresis in the presence of sodium dodecyl sulphate to monitor conversion of the monomeric form of a-toxin (molecular weight = 36 000) to the al,, aggregate. The widely differing lipids varied in the order diglyceride > lecithin > cholesterol > lysolecithin in polymerinducing activity. No individual component was as efficient as a mixed dispersion of lecithin, cholesterol and dicetyl phosphate (molar ratio 70 : I o : 20) in inducing polymerization. In general our observations indicate that there is no specific lipid inducer and that the outcome of the interaction between staphylococcal a-toxin and biological membranes probably depends on the location of lipids in the membrane and their distribution in relation to one another. Also the results with diglyceride confirm our earlier suggestion that a-toxin can react hydrophobically with lipids.

Campylobacter jejuni is a major cause of human diarrhoeal disease, but specific virulence mechanisms have not been well defined. This blinded study was undertaken with 40 C. jejuni isolates from different sources to determine their haemolytic, cytotoxic and adhesion and invasion activities towards mammalian cells. The results were correlated with source of isolation and genetic makeup by amplified fragment length polymorphism (AFLP) typing. The isolates had variable degrees of haemolytic activity against rabbit erythrocytes and cytotoxicity towards CaCo-2, HeLa and Vero cells. The data indicated that the haemolytic and cytotoxic activities were due to separate factors. A range of cytotoxicity was exhibited, whereby some strains had no activity against the target cells and others had activity against all three cell lines. Certain strains had activity against CaCo-2 cells but little or no activity against the other cells, while others exhibited the opposite phenotype. The data suggested that the cytotoxicity assay with the different cell lines may have detected more than one cytotoxin. A wide variation between isolates was observed for both adherence and invasion with all three cell lines, yet, overall, the strains showed a significantly greater invasion capacity for CaCo-2. There was no clear relationship between source of isolation or disease manifestation and possession of statistically significantly higher levels of particular virulence-associated factors although, in some cases, a correlation between cytotoxicity and cell invasion was evident. Five AFLP clusters, each representing two to eleven isolates with similar profiles, were observed at the 90 % similarity level. Some AFLP groups contained isolates with a common serotype, but each group had C. jejuni isolates from more than one source with the exception of group IV, which contained only human isolates. Isolates with high cytotoxic activity against CaCo-2 cells were confined to groups I, III and IV and a group of unrelated strains (U). Group II isolates had uniformly low cytotoxicity. Isolates in groups I, V and U were more invasive for CaCo-2 cells than isolates in groups II, III and IV. The strain differences in cytotoxicity or invasion did not correlate with source of isolation.

A correlated electron microscopy and biochemical study of the effects of staphylococcal a-toxin on rabbit erythrocyte membrane structure has been carried out. Using several criteria, no evidence was obtained for the involvement of a proteolytic mechanism in the mode of action of this toxin.After toxin treatment, ghosts examined by freeze-etching showed changes in micromorphology consistent with a hydrophobic interaction between toxin and membrane.