Cellulitis, acute inflammation of the dermis and subcutaneous fat, often associated with fever, lymphadenopathy, and elevated leukocyte count, is classically viewed to be caused by bacterial invasion of the skin by group A streptococci. Staphylococcus aureus that typically produces walled-off dermal abscesses can also at times be associated with a spreading plaquelike cellulitis. When this process of deep cutaneous inflammation is present on the face, the term erysipelas is normally used. While streptococci are viewed to be the primary cause of erysipelas, Haemophilus influenzae can cause such a lesion in children.1 Other organisms, however, have been isolated from patients with cellulitis, including Escherichia coli, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Pasteurella multocida.2-5 The possibility of an unusual organism must be considered in the immunocompromised patient or in any patient who fails to respond to otherwise appropriate therapy for the usual causative organisms.
Despite the uniform agreement that streptococci, particularly group A, are the major causative oragnism in cellulitis and erysipelas
Leyden JJ. Cellulitis. Arch Dermatol. 1989;125(6):823-824. doi:10.1001/archderm.1989.01670180095015