Sera from patients suffering from the autoimmune skin diseases pemphigus vulgaris and bullous pemphigoid were used to demonstrate the presence of intercellular substance (ICS) or bullous pemphigoid antigen (BPA) on the surface of the schistosomula of Schistosoma mansoni which had penetrated mouse and human cadaver skin, and mouse skin percutaneously. Both ICS and BPA were absent from mechanically transformed schistosomula or those formed in the peritoneal cavity of mice. Schistosomula which penetrated slowly through mouse or human skin in vitro, acquired more ICS or BPA than those which penetrated rapidly.

During percutaneous infections of mice, schistosomula recovered from skin after 2h and 24h had acquired large quantities of these materials whereas those which were recovered from skin after 10min had no detectable ICS or BPA. These materials must be shed during subsequent migration since schistosomula from lungs and liver, and 7-week old adults do not possess them.

Histological examination of both mouse and human skin revealed that the schistosomula remained in the epidermis for varying lengths of time. Schistosomula which remained there for more than 2h became vacuolated, whereas schistosomula which were present in the dermis at 2h appeared undamaged.

On cercarial penetration of human skin, the granular layer of the epidermis became disrupted or condensed. The implications of these findings are discussed.

The mechanisms of interaction are discussed in general terms; this is followed by a review of interaction which may occur in tinea paedis.

The production of penicillin-like and other antibiotics by dermatophyte fungi in lesions of athletes foot may result in the selection of an antibiotic-resistant bacterial flora which, perhaps by production of antibiotic or other secondary metabolites, can reduce the viability of the fungi. The effect on the host is to bring about a change from a fungal skin lesion which is dry and scaly to a bacterial lesion which is macerated and malodorous.

Human skin propionibacteria have been shown to produce, in vitro, a wide range of inhibitory substances including bacteriocins, bacteriolytic enzymes, bacteriophages and low molecular weight metabolites (e.g. ammonia, propionic acid). Some or all of these substances may play a role in the ecology of cutaneous populations of micro-organisms and may be involved in maintaining the balance of the normal flora. There is no evidence to suggest that they deter or exclude other transient bacteria including pathogens. Similarly, evidence in support of the in vivo production of growth inhibitors by propionibacteria with activity against other skin micro-organisms is lacking (except for bacteriophage and propionic acid) so that their potential role in controlling cutaneous populations must be interpreted with caution.

An in vivo staining technique has been developed for the demonstration of micro-organisms on human skin. This technique permits the study of the relationship between micro-organisms and the stratum corneum and its associated structures. It also aids an understanding of the factors involved in the nutrition and survival of micro-organisms on the skin surface.

In skin sites with large populations of coryneform species the bacteria tend to accumulate at the edges of corneocytes. This tendency is not shared by members of the micrococcaceae.

Agar impressions of the skin surface confirm observations of other workers and suggest that the surface of the stratum corneum is composed of domed corneocytes with a network of troughs or channels surrounding them. It is proposed that the association of coryneform bacteria with the edges of corneocytes may be due to the creation of an environment within the troughs which favours microbial colonisation.

The collected evidence of the Symposium illustrates that sufficient information is now available to enable initial broad definition of the skin surface ecosystems for the different animal classes. As may be expected more is known about the ecosystems of classes (mammal, fish) and genera (e.g. Bos, Salmo) of commercial interest. A notable exception is the skin surface of the bird, about which, despite the development of intensive poultry husbandry, surprisingly little is known. The work to date on the morphology, chemical nature and inhabitants of the different ecosystems, however, provides only limited data on the dynamic processes, actions and co-actions occurring within them and the interchange of inhabitants between them. In particular, the role of the surface micro-climates in the development, survival and transfer of micro-organisms has still to be determined. Our present knowledge is thus almost entirely limited to recognition of the basic elements of the skin surface ecosystems and there is still a paucity of data on the variation between species, individuals and body regions, some of which appear to have specialised functions or like the joints of arthropods may be more susceptible to colonisation and invasion. Nonetheless, although the definition of the various surface ecosystems has by no means been completed, a stage has been reached where identification, classification and comparison of the defence mechanisms operating at the skin surface of different classes of animals can be attempted.