Microbiology of the interdigital web

The microbiology of the interdigital toe areas is a complex subject that has been partially elucidated by the results of many investigations. Stable resident populations must be maintained in these moist and warm skin surfaces in order to prevent colonization of potential pathogens and overgrowth of innocuous residents. This balanced population of normal flora can be upset by conditions of increased hydration or prolonged occlusion. Population densities invariably increase as the moisture content of skin increases. ^2,4,16 Fluorescent diphtheroids, nonlipophilic diphtheroids, and gram-negative bacilli preferentially flourish under such conditions. Concomitantly, hydrated skin also is macerated easily, and this predisposes individuals to develop superficial mycotic infections of the foot. ^1,5 Stable resident populations thereby become affected by the diffusible antibiotic-like substances produced by dermatophytic fungi, ^28–30 Resistant populations of aerobic cocci, nonlipophilic diphtheroids, and gram-negative bacilli become dominant over sensitive cocci and diphtheroids in such dermatophyte infections. Whereas the keratinolytic activity of dermatophytes was initially responsible for the pruritic, scaling lesions of mild athlete's foot, it is the proteolytic activity of brevibacteria and gram-negative bacilli that is responsible for the development of severe lesions. ^5,32 Coincidently, large populations of such microorganisms generate copious amounts of metabolic by-products such as carbon dioxide and methanethiol, that are toxic to fungi.6'30 Dermatophytes thus become quite difficult to isolate in many cases of severe athlete's foot. ^13,14,32 In such exacerbated intertriginous infections, treatment with drying agents and antibacterial substances is quite effective in alleviating symptomatology.^16,32 However, dermatophytes may persist or reinfect the interdigital web and thus maintain an asymptomatic form of chronic athlete's foot. In order to prevent further exacerbations, the interdigital web surfaces must be kept dry, and antimycotic therapy must be instituted to ultimately free the individual of the dermatophytic agent. Only under these circumstances will stable populations of resident normal flora and healthy interdigital web surfaces be maintained.