An Atypical Manifestation of Cellulitis Induced by Proteus mirabilis

Cellulitis is a common bacterial skin infection typically caused by organisms such as Streptococcus and Staphylococcus species. Proteus mirabilis (P. mirabilis), a gram-negative rod more often linked to urinary tract infections, is not a frequent cause of cellulitis. However, certain biological traits like motility and the ability to form biofilms can occasionally contribute to infections in compromised tissue. This case discusses an uncommon presentation of cellulitis involving P. mirabilis and its clinical management. An 81-year-old woman with a history of vascular disease and other chronic conditions presented with a red, swollen wound on her lower leg after a minor injury. Initial treatment with empiric antibiotics did not resolve the symptoms, and wound cultures later revealed P. mirabilis. Treatment was adjusted to amoxicillin-clavulanate, but persistent inflammation required a second course of antibiotics due to the patient's sulfa allergy. The infection eventually resolved without systemic complications. Although not a typical skin pathogen, P. mirabilis may occasionally be found in such infections, particularly when initial therapies are ineffective. This case emphasizes the importance of considering less common organisms in cellulitis cases that do not improve with standard treatment. Tailoring antibiotics based on culture results is essential to achieving resolution and avoiding complications. A broad diagnostic approach can be valuable in managing unusual or resistant infections.