Bacterial diseases in dogs are usually not contagious from dog to dog; instead they are usually the result of wound colonization, opportunistic infections secondary to decreased resistance (often the result of viral infections), or secondary to other conditions (pyoderma secondary to skin allergies or pyometra secondary to cystic endometrial hyperplasia). These examples are not considered infectious diseases because they do not satisfy Koch's postulates – for example "Staphylococcus intermedius", a commonly isolated bacteria from skin infections in dogs, would not cause pyoderma when introduced to a healthy dog. In all likelihood that type of bacteria is already present on the skin of a healthy dog.