Bacterial Infection of the Skin in Dogs

Many species of bacteria normally reside on the skin of dogs without causing any signs. Infection develops when conditions create an environment where bacteria can proliferate. This could be a flea infestation, an allergic reaction, a wound, or an underlying disease that depletes the immune system. Many different types of bacteria may be involved, but the most common species associated with pyoderma in dogs is staphylococcus pseudointermedius. The name pyoderma comes from the Greek words for “pus” and “skin,” so this term refers to any bacterial skin infection that exudes pus. Dogs may have red itchy patches of pustules that seep blood and discharge when they break. Severe infections may develop into painful ulcerations and boils. Bacteria flourish in moist conditions, so many pyoderma infections are caused by another condition that adds oil and moisture to the skin. Signs are more often found in the skin folds, or around areas of broken irritated skin. One-time infections are often treatable with antibiotics, but some dogs may have recurrent symptoms due to an allergy or an endocrine imbalance like hypothyroidism or Cushing’s disease. In this case, the underlying condition will also need to be treated. Recurrent infections can be more problematic, especially if they lead to the development of antibiotic resistant bacteria.

Dogs can develop an infection when normal bacteria in the skin proliferate excessively. Infected dogs can have areas of redness, rash-like pustules, and hair loss.

Signs can range from mild irritation to severe and painful infection. See your veterinarian if you notice any of the following signs.

• Pimple-like pustules on the skin
• Dry patches of flaking skin
• Itching
• Crusted skin
• Infected hair follicles
• Alopecia (hair loss)
• Hair standing on end
• Seeping of blood or pus
• Swelling or ulcerated skin
• Odor

Types

Veterinarians use several different terms to define types of pyoderma.

• Simple – a one-time response
• Complex – infections that are recurrent or associated with an underlying disease
• Focal – infection developing in a specific area
• Generalized – covering the entire body
• Superficial – infection of the epidermis (outer layer of the skin) and hair follicles
• Deep – more severe infection involving the dermis (deeper layer of the skin)

Pyoderma can be associated with many different conditions and veterinarians often struggle to find the exact cause. The following conditions are often related.

• Flea infection
• Allergic reaction
• Any chronic form of dermatitis
• Fungal or yeast infection (Malassezia)
• Wound
• Broken skin from scratching
• Poor grooming
• Endocrine imbalance that reduces lymphocyte counts like Cushing’s disease (hyperadrenocorticism), and hypothyroidism
• Hereditary (some dogs are more prone to developing infection)

The veterinarian will perform a complete physical examination. Signs of skin infection will suggest pyoderma. Blood and urine tests will help to determine the underlying cause. Cell cultures may be taken of the infected area and examined microscopically to determine what organisms are present. Malassezia fungal infections are commonly found concurrent with bacterial pyoderma. The veterinarian will also check for the presence other parasites. In some cases, the culture may be sent to a lab to analyze the bacteria’s resistance to antibiotics and determine the best treatment.

The veterinarian will need to know your dog’s medical history and current medications. If your dog is taking a steroid, or another medication that suppresses the immune system this is important since it will limit the effectiveness of an antibiotic. Any prior skin infections or treatment with antibiotics is also relevant.

Most dogs with pyoderma will be treated with an oral antibiotic as well as topical sprays and shampoos. Many different antibiotics may be prescribed. The veterinarian will choose the one that best fits your dog’s infection. Antibiotic treatment will last from 2 to 6 weeks. Your dog will need to continue taking the medication at least a week after the symptoms of infection have been resolved in order to ensure that bacteria don’t survive and develop resistance.

Your will need to bathe your dog with a medicated shampoo several times a week during treatment. Dogs with severe, deep, pyoderma may need to be shampooed daily. Your veterinarian may prescribe a shampoo containing benzoyl peroxide, chlorhexidine, or another antiseptic agent. A topical antibacterial ointment or spray will likely be prescribed also.

To avoid recurrence, treatment will also need to focus on the underlying cause. The veterinarian will prescribe medication to treat hypothyroidism or Cushing’s disease. Different treatment could be needed depending on the cause of these conditions. If a food allergy is suspected, the veterinarian may recommend a diet change or suggest eliminating different foods to find the cause of the allergy. Treatment may also be needed for fungal infection, parasites, or fleas.

Pyoderma is not a life-threatening problem, but it can cause your dog a lot of pain and discomfort. Fortunately, most infections are treatable, and it is likely your dog will make a full recovery. Chronic and recurrent infections without a known cause can pose more of a problem. Regular bathing and grooming can help, as well as washing your dog’s bedding frequently. Some dogs may need to follow a strict diet to avoid an allergic reaction. Others may need lifelong medication to treat an endocrine imbalance. If this is the case, frequent check-ups will be necessary so the veterinarian can monitor your dog’s condition and adjust the dosage.