Other bacterial infections
Diseases due to commensal overgrowth
Sometimes, ‘normal’ commensals can result in disease. Among the most common are the following:
Pitted keratolysis. Overgrowth of resident micro-organisms, that digest keratin; occurs with occluding footwear and sweaty feet (Fig. 1). Malodorous pitted erosions and punched out, discoloured areas result. Better hygiene, topical neomycin or soaks with 0.01% aqueous potassium permanganate or 3% aqueous formaldehyde usually help.
Erythrasma. A dry, reddish–brown, slightly scaly and usually asymptomatic eruption that affects the body folds (Fig. 2). It fluoresces coral pink with Wood’s light, owing to the production of porphyrins by the corynebacteria. Imidazole creams, topical fusidic acid or oral erythromycin are effective.
Mycobacterial infections
Mycobacterium tuberculosis and M. leprae (p. 60) are the most important mycobacteria in human disease, although other species can cause infections. In western countries, tuberculosis (TB) has recently shown resurgence, related to immigration and co-infection with HIV. In the developing world, 50% of HIV-infected individuals also have TB. TB can produce a number of cutaneous manifestations (Table 1).
Table 1 Skin manifestations of tuberculosis
Lupus vulgaris
Clinical presentation
Lupus vulgaris follows primary inoculation and develops in individuals with some immunity. It begins as painless reddish–brown nodules that slowly enlarge to form a plaque (Fig. 3), leaving scarring and sometimes destruction of deeper tissues such as cartilage. Presentation in the elderly is often due to reactivation of inadequately treated pre-existing disease.
