UMEM Educational Pearls


41year-old male without past medical history presents with the image below. What's the diagnosis and what's the most likely causative organism?


Gram-Negative web-space infection; most common etiologic organism is Pseudomonas

Gram Negative Web-space Infections

Gram-negative infections may occur in toe web-spaces of healthy patients, especially in areas with hyperhidrosis (excessive perspiration) and macerated skin.

Common organisms include Pseudomonas; others include Corynebacterium minutissimum (causes erythrasma, chronic superficial infection of the intertriginous areas of the skin), and other gram-negative bacteria

Woods-light examination may be clinically helpful if Pseudomonas is suspected (fluoresce green) and erythrasma will fluoresce coral red. KOH direct examination for fungal elements may show the presence of dermatophytes or Candida. 


  • Moisture reduction of web-spaces by keeping feet dry (e.g., open-toed shoes, drying powders, etc.)
  • Uncomplicated, superficial infections respond well to topical agents active against the causative organisms (e.g., gentamycin ointment)
  • Severe or complicated infections may require oral / parenteral antibiotics (i.e. third-generation cephalosporin or quinolone or aminoglycoside) plus antifungals; tissue removal/surgical debridement may be required.


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Wolff, K., & Johnson, R. J. (2009). Fitzpatrick's Color Atlas and Synopsis of Clinical Dermatology. (6th ed., pp. 662-664;698). McGraw-Hill.