What is the expected bacterial etiology of typical cases of cellulitis?

In typical cases of cellulitis, the most common bacterial pathogens involved are Staphylococcus aureus and Streptococcus species, particularly Streptococcus pyogenes (Group A Streptococcus). These bacteria are part of the normal flora of the skin and can invade the dermal and subcutaneous tissues, especially following breaks in the skin such as cuts, abrasions, or insect bites.

Staphylococcus aureus, including methicillin-resistant Staphylococcus aureus (MRSA), is a significant causative agent due to its ability to cause skin infections and its prevalence in both community and hospital settings. Streptococcus pyogenes is often associated with more classic presentations of cellulitis, as it can lead to complications like necrotizing fasciitis or tennis elbow due to its virulence.

In contrast, the other options represent less common etiologies for cellulitis. Escherichia coli and Pseudomonas aeruginosa are more often implicated in infections related to specific conditions, such as diabetic foot ulcers or immunocompromised states, rather than typical cellulitis. Streptococcus pneumoniae primarily causes respiratory infections and is not typically involved in cellulitis. Clostridium perfringens is associated with gas gangrene