Staphylococcus pseudintermedius is a type of bacteria commonly found on the skin, in the nasal passages, and within the oral cavity of healthy dogs. While typically harmless, this bacterium is an “opportunistic pathogen,” meaning it usually only causes infections when there is an underlying health issue or a disruption to the skin’s natural defenses.
The Role of S. Pseudintermedius in Canine Health
The skin of dogs hosts a complex community of microorganisms where S. pseudintermedius normally resides without causing harm. However, certain factors can disrupt this balance, allowing the bacteria to multiply excessively and lead to infection. These triggers often compromise the skin barrier or suppress the immune system.
Common underlying conditions that predispose dogs to S. pseudintermedius infections include allergies (environmental, flea, or food reactions), which cause skin inflammation and itching. Endocrine disorders, like hypothyroidism or Cushing’s disease, also weaken the skin’s defenses. External factors such as parasitic infestations, physical damage from scratches or wounds, or excessive moisture can breach the skin barrier, enabling the bacteria to proliferate.
Signs of a Staph Infection
When S. pseudintermedius causes a skin infection, several clinical signs appear. The skin may show redness and inflammation, often with small, pus-filled bumps (pustules). As these rupture, they can form circular crusts with a ring of scaling, called epidermal collarettes, which indicate bacterial skin infection.
Dogs often experience intense itching, leading to self-trauma and hair loss. A noticeable odor might also develop. In some cases, rapidly developing, painful, and moist inflamed lesions, commonly called “hot spots,” can emerge.
S. pseudintermedius frequently causes ear infections (otitis externa). Signs include frequent head shaking, persistent scratching at the ears, and discharge or an unpleasant smell. This bacterium can also infect surgical wounds or, less commonly, lead to urinary tract infections.
Diagnosis and Treatment Approaches
Veterinary diagnosis of an S. pseudintermedius infection begins with a visual examination. Skin cytology is often performed to confirm the presence of bacteria and inflammatory cells. A sample is collected from the lesion, which is then stained and examined under a microscope.
For recurrent or severe infections, or when initial treatments are unsuccessful, a bacterial culture and sensitivity test is recommended. This laboratory test identifies the specific type of bacteria and determines which antibiotics will be effective. The results guide the veterinarian in selecting the most appropriate antibiotic therapy.
Treatment involves topical or systemic therapy. Topical therapy involves applying medicated shampoos, mousses, sprays, or wipes directly to the affected skin. This is often the initial approach for localized infections and can be highly effective. For widespread or deep-seated infections, oral antibiotics are prescribed. Administer the full course of antibiotics exactly as directed, even if symptoms improve, to ensure complete eradication and minimize recurrence or resistance development.
Understanding Antibiotic Resistance (MRSP)
A significant concern in treating S. pseudintermedius infections is the emergence of Methicillin-resistant Staphylococcus pseudintermedius, commonly abbreviated as MRSP. MRSP refers to strains of this bacterium that have developed resistance to multiple common antibiotics, including methicillin and often other drug classes. These resistant strains pose a challenge because they limit the available treatment options, making infections more difficult to resolve.
The presence of MRSP underscores why bacterial culture and sensitivity testing is important, as it helps veterinarians select an antibiotic that the specific bacterial strain is still susceptible to. While MRSP infections are not inherently more aggressive or dangerous than non-resistant strains, their resistance means they are harder to eliminate. Preventing antibiotic resistance is a shared responsibility, emphasizing the importance of using antibiotics only when necessary and strictly adhering to veterinary instructions regarding dosage and duration of treatment.
Prevention and Management at Home
Long-term management and prevention of recurrent S. pseudintermedius infections involve identifying and addressing underlying health issues. If allergies are the root cause, consistent management through diet changes, environmental controls, or specific medications is necessary. Regular flea and tick prevention also helps avoid skin irritation that can lead to infection.
Supportive care, such as routine bathing with medicated shampoos prescribed by a veterinarian, can help maintain skin health and reduce bacterial populations. This proactive approach helps strengthen the skin barrier and minimize opportunities for bacterial overgrowth. Transmission of S. pseudintermedius from dogs to humans is very rare, typically posing a risk only to individuals with severely compromised immune systems. Basic hygiene practices, such as thorough hand washing after handling an infected dog, are sensible precautions.