Pyoderma in Dogs (Bacterial Skin Infection, Pus in the Skin)

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Pyoderma in Dogs (Bacterial Skin Infection, Pus in the Skin)

By: Dr. Mark Thompson

Section: Veterinary Care In-depth

Diagnosis In-depth

Your veterinarian will take a thorough medical history and examine all body systems. Other medical tests will be necessary to establish the diagnosis.

  • Microscopic examination. Your veterinarian may open a pustule and apply the material within the pustule to a microscope slide. The slide is then stained and viewed under a microscope. The presence of pyoderma will reveal bacteria with white blood cells, especially neutrophils.

    He may also make an impression of the discharge from a draining sore seen with deep pyoderma by pressing a slide to the lesion. This slide can be stained and examined under the microscope.

  • Culture and antibiotic sensitivity. In cases of deep pyoderma lesions, this test must be done to identify the bacteria responsible and to select the most appropriate antibiotic. Cultures of superficial pyoderma pustules are rarely done, since they nearly always grow Staphylococcus intermedius.


  • Visualization. Your veterinarian can usually diagnose surface pyoderma by visualization of the lesion. Hot spots have a characteristic appearance of a moist, red skin lesion with sudden hair loss. Skin fold pyoderma is a red, moist lesion associated with a skin fold. Hot spots are triggered by an itchy skin problem. Thus, diagnostics to determine the itchy underlying cause may be necessary, especially with recurrent hot spots. Often, flea allergy is the culprit.

  • Superficial pyoderma may cause a dog to be itchy. This can cause confusion in the diagnostic process since itching may lead to pyoderma. The veterinarian may ask if your dog's lesions preceded the itching or if the itching preceded the lesions. If the itching came first, then a pruritic underlying cause is suspected. If the lesions appeared first, then immune suppression may be the cause.

    If itching is suspected, the following tests may be done to determine the source of the problem:

  • Examination of the skin and hair with a flea comb for fleas and lice

  • A skin scraping to look for mites and other microscopic parasites

  • Fungal cultures to rule out ringworm fungus (dermatophytes). These skin fungi may cause itching and lead to a secondary pyoderma.

  • Allergy testing or a food trial to rule out food allergy in chronic cases of pyoderma

    In cases where superficial pyoderma is suspected to be caused by immune suppression and in all cases of deep pyoderma, tests are needed to look for the cause of the immune deficiency. Examples include:

  • Thyroid assays to see if the thyroid gland is making enough thyroid hormone

  • Tests for Cushing's disease (hyperadrenocorticism), a disease where the adrenal glands make too much of a hormone called cortisol. One effect of the excessive cortisol can be immune suppression.

    Severe, chronic illnesses, such as cancer, can suppress the immune system.

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