Pyoderma is a bacterial infection of the skin. It can occur when the skin’s natural defenses break down, allowing common skin bacteria to multiply out of control (called overgrowth). Bacteria from another source may also take hold when given the opportunity. Other organisms, such as yeast and fungal organisms, can take advantage of the skin changes that occur with pyoderma and establish their own infections. Dogs and cats of any age can be affected by pyoderma.