Pyoderma can be caused by Mange (mites)

Mange ... what's eating your pets?: "Sarcoptes scabiei var. canis, the mite of sarcoptic mange, an intensely pruritic, transmissible skin disease, is a frequent parasite of dogs, and to a lesser degree, cats and humans in Singapore (S. scabiei var. cuniculi, the rabbit scabies mite, is also endemic here). The mites prefer lightly haired regions, and are most common on the elbows, hocks, ears, chest and abdomen. The disease spreads rapidly, and the entire body may be colonised by mites. The female mite tunnels through the skin, depositing eggs as she goes. Once these ova hatch, the larvae burrow to the surface where they browse and feed. The larval stage then rests in a 'moulting pocket' and develops to the nymph stage. These also graze the skin surface before returning to moult to the adult stage. The life-cycle is completed in approx. 3 weeks. Transmission occurs mostly through direct contact with an infected animal.
MANGE:

Mange ScabieInitially the pruritis is mild until the host develops a hypersensitivity to the mite, usually 3 to 4 weeks post-exposure. At this time, the itching becomes intense - hence the common name 'scabies' from the French scabere 'to scratch' - leading to self-induced traumatic wounds that exude serum, forming crusts.
However, the presenting signs of sarcoptic mange can be varied and misleading, some dogs never developing 'classical' lesions. Secondary pyoderma (bacterial infection) and alopecia are common signs, and may be confused with atopic (allergic) dermatitis, food allergies or Staphylococcal pyoderma. Microscopic demonstration of the mites from a skin scraping establishes the diagnosis, although in some cases a response to therapy is needed for confirmation.
Sarcoptes mites are quite species-specific, and usually cannot complete their life cycle on a non-definit"

--bulldog's don't have the best immune system due to their breeding
E.S.