Other bacterial infections

Diseases due to commensal overgrowth

Sometimes, ‘normal’ commensals can result in disease. Among the most common are the following:

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  Pitted keratolysis . Overgrowth of resident microorganisms that digest keratin; occurs with occluding footwear and sweaty feet ( Fig. 28.1 ). 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.

  

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  Erythrasma. A dry, reddish–brown, slightly scaly and usually asymptomatic eruption that affects the body folds ( Fig. 28.2 ). 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.

  

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  Trichomycosis axillaris. Overgrowths of corynebacteria form yellow concretions on axillary hair. Topical antimicrobials usually effect a cure.

Mycobacterial infections

Mycobacterium tuberculosis and M . leprae ( Chapter 26 ) 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. Individuals treated with anti-TNF biologics (e.g. for psoriasis) are at particular risk and latent TB should be excluded before treatment. TB can produce a number of cutaneous manifestations ( Table 28.1 ).