Final answer:
Cellulitis is commonly caused by S. pyogenes and presents with symptoms such as a warm, red, and painful skin rash. Penicillin is the standard treatment, and diagnosis involves immunological tests to detect streptococcal or staphylococcal bacteria as possible pathogens.
Step-by-step explanation:
Cellulitis is an infection of the skin and is commonly caused by the bacterium Streptococcus pyogenes (S. pyogenes), also known as Group A streptococci (GAS). Symptoms and signs (S&Sx) of cellulitis include a painful, warm, red rash that can spread rapidly. In more severe cases, such as those mentioned in the case of necrotizing fasciitis, there may be blistering, gas pockets under the skin, rapid progression of infection, and a putrid smell from the draining pus.
Penicillin is typically prescribed for treating cellulitis because resistance among streptococci has not been widely observed at this time. Several immunological tests, such as agglutination reactions and ELISAs, are used to detect the presence of streptococcal bacteria. In some cases, community-acquired and hospital-acquired staphylococcal infections may complicate the clinical picture, as Staphylococcus aureus can also be a causative agent for skin infections.