Which of the following is a common gram-negative agent associated with cellulitis?

Cellulitis is primarily a skin and soft tissue infection that can be caused by various pathogens, including both gram-positive and gram-negative bacteria. Among these, Escherichia coli (E. coli) is recognized as a common gram-negative agent associated with cellulitis, particularly in specific populations or circumstances, such as cases involving water exposure, diabetes, or immunocompromised states. E. coli is often found in the gastrointestinal tract and can enter the bloodstream or soft tissues through breaks in the skin, leading to infections.

While Staphylococcus aureus and Streptococcus pneumoniae are significant pathogens in cellulitis - with Staphylococcus being one of the most common agents overall due to its prevalence on the skin - they are gram-positive. Clostridium perfringens is also an important bacterium, particularly associated with gas gangrene rather than typical cellulitis, as it is more commonly found in environments contaminated with soil or fecal matter. Therefore, the recognition of E. coli as a gram-negative agent highlights its role in certain cellulitis cases and reinforces the importance of considering a broad differential diagnosis in skin infections.