Sometimes. It can be in some instances.
What's the cause. Cellulitis is basically a visible inflammation (itis) of the skin and soft tissues (red, hot, swollen and tender) . It can be caused by many things including sunburn (radiation), trauma (sprained ankle) or poor vein circulation (stasis dermatitis). It need not be caused by bacteria. If you have repeated episodes of this, get to a wound care or vascular specialist, the diagnoses you have is wrong.
Skin infection. Bactrim (sulfamethoxazole and trimethoprim) is an excellent antibiotic used to treat MRSA or bad staph infection. If the bacteria is other than mrsa, it's better to use other antibiotics to treat usual staph infections. This is to prevent the MRSA from developing resistance to Bactrim (sulfamethoxazole and trimethoprim) which is one of the best ones to treat that infection.