Clinical meaning
Cellulitis is an acute, spreading bacterial infection of the deeper layers of the skin, specifically the dermis and subcutaneous tissue. It is one of the most common skin infections encountered in clinical practice and a frequent reason for hospital admission. Unlike superficial skin infections such as impetigo, cellulitis involves deeper tissue planes and can progress to life-threatening complications if not treated promptly. The infection typically begins when bacteria enter through a break in the skin barrier. Common entry points include cuts, abrasions, surgical wounds, insect bites, dermatitis, tinea pedis (athlete's foot between the toes), venous stasis ulcers, and intravenous catheter insertion sites. Even microscopic breaks in the skin that are not visible to the naked eye can serve as portals of entry. The most common causative organisms are Group A Streptococcus (Streptococcus pyogenes) and Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA) in healthcare and community settings. Once bacteria penetrate the skin, they multiply in the dermis and subcutaneous tissue. Bacterial virulence factors (enzymes such as hyaluronidase, streptokinase, and DNase) break down connective tissue components, facilitating rapid lateral spread through tissue...