Taken from a WebMD Cellulitis ArticleWhat causes cellulitis?
Staph (Staphylococcus aureus) is the most common bacteria that causes cellulitis.
Strep (Group A Streptococcus) is next most common bacteria that causes cellulitis. A form of rather superficial cellulitis caused by strep is called erysipelas; it is characterized by spreading hot, bright red circumscribed area on the skin with a sharp raised border. The so-called "flesh-eating bacteria" are, in fact, also a strain of strep which can in severe cases destroy tissue almost as fast as surgeons can cut it out.
Cellulitis can be caused by many other types of bacteria. In children under six, H. flu (Hemophilus influenzae) bacteria can cause cellulitis, especially on the face, arms, and upper torso. Cellulitis from a dog or cat bite or scratch may be caused by the Pasturella multocida bacteria, which has a very short incubation period of only four to 24 hours. Cellulitis after an injury from a saltwater fish or shellfish (like a fish bite, a puncture from a fish spine, or a crab pinch) can be due to the Erysipelothrix rhusiopathiae bacteria. These same bacteria can also cause cellulitis after a skin injury on the farm, especially if it happened while working with pigs or poultry.
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