Antibiotic-resistant Bacterial Infections in Dogs

Several different species of staphylococcus (staph) bacteria can affect people and dogs. Many people carry S. aureus bacteria without symptoms, but these bacteria can take advantage of a weakened immune system or a skin injury to multiply and cause an opportunistic staph infection. Dogs rarely carry S. aureus, but they may catch the infection from their human owners. On the other hand, dogs naturally carry another strain of bacteria, S. pseudintermedius which, like S. aureus in humans, is usually asymptomatic unless the dog has an open wound or a weakened immune system. S. pseudintermedius can be zoonotic, but it doesn’t usually cause severe infection in humans. In dogs, staph infections typically affect the skin, with areas of redness, peeling and crusted or ulcerated skin. Most are responsive to a penicillin-type beta lactam antibiotic, such as methicillin, and the symptoms clear up easily with treatment. Some strains of S. aureus or S. pseudintermedius, can develop resistance to traditional antibiotics, however; this type of methicillin-resistant infection is called MRSA or MRSP depending on the strain of bacteria. Resistance can take the form of a resilient coating, or proteins that are not affected by the antibiotic. The ability to withstand antibiotics is often passed on genetically to subsequent generations of bacteria, so antibacterial-resistant infections are more common in animals that have received prior treatment. They are also more common in dogs taking drugs that suppress the immune system such as prednisone, corticosteroids, or chemotherapy treatment for cancer. MRSA and MRSP are not more virulent than other types of staph infections, but they are harder to treat and may take more time to heal.

Dogs are susceptible to the same type of staphylococcus bacteria that causes staph infections in humans. Most symptoms clear up with antibiotic treatment, but in some cases, the bacteria can develop resistance to traditionally prescribed antibiotics. These antibiotic-resistant infections are called MRSA or MRSP depending on the strain of bacteria involved.

Dogs with high numbers of staph bacteria can develop a severe skin infection. See a veterinarian if you notice any of the following symptoms.

• Pimples
• Red spots
• Red patches (erythema)
• Peeling or itching skin
• Crusted skin
• Ulcerated areas
• Weeping areas and pus
• Loss of fur
• Persistent skin infection (pyoderma) that doesn’t respond to treatment

Types

S. aureus and S. pseudintermedius are the most common types of staph bacteria found in people and dogs respectively. S. schleiferi is another recently identified strain found in both people and dogs that can develop the same kind of antibiotic resistance.

• MRSA – methicillin-resistant Staphylococcus aureus
• MRSP – methicillin-resistant Staphylococcus pseudintermedius
• MRSS – methicillin-resistant Staphylococcus schleiferi
• MDR (multiple drug resistant) infection – another name for all types of this condition 

These conditions can make it more likely for your dog to develop an antibiotic-resistant bacterial infection.

• Weak immune system
• Wounds or damaged tissue
• Recent surgery
• Frequent hospital visits
• Poor hygiene and conditions of overcrowding
• Prior infection treated with antibiotics
• Failure to properly clean pus or infected fluid before treatment
• Failure to administer the proper number of antibiotic doses
• Immune suppression drugs taken at the same time as the antibiotic
• Other drugs or foods that interfere with the antibiotic function

The veterinarian will suspect a staph infection based on your dog’s symptoms. A cellular culture will be analyzed under a microscope to check for bacteria as well as analyze the possibility of a simultaneous fungal infection. This may not directly determine the species or strain of bacteria, but the veterinarian will likely prescribe an empiric antibiotic immediately. If the infection does not respond to treatment, a culture will be taken and sent to a lab where the specific strain of bacteria will be identified and analyzed for its resistance to antibiotics. The veterinarian will keep your dog on the original antibiotic until the bacteria has been identified as resistant.

If your dog has had prior infections that did not respond to treatment, this will make MRSA or MRPA more likely. The veterinarian will need to know your dog’s medical history, including past and present medications, especially immunosuppressant treatment. Any other recent illnesses, injuries or surgeries will also be relevant. The veterinarian will check your dog’s vital signs and take blood and urine samples to evaluate his overall health.

The veterinarian will suspect a staph infection based on your dog’s symptoms. A cellular culture will be analyzed under a microscope to check for bacteria as well as analyze the possibility of a simultaneous fungal infection. This may not directly determine the species or strain of bacteria, but the veterinarian will likely prescribe an empiric antibiotic immediately. If the infection does not respond to treatment, a culture will be taken and sent to a lab where the specific strain of bacteria will be identified and analyzed for its resistance to antibiotics. The veterinarian will keep your dog on the original antibiotic until the bacteria has been identified as resistant.

If your dog has had prior infections that did not respond to treatment, this will make MRSA or MRPA more likely. The veterinarian will need to know your dog’s medical history, including past and present medications, especially immunosuppressant treatment. Any other recent illnesses, injuries or surgeries will also be relevant. The veterinarian will check your dog’s vital signs and take blood and urine samples to evaluate his overall health.

Most dogs with an antibiotic-resistant bacterial infection will make a full recovery. Once a dog has had one drug-resistant infection, however, the likelihood of a repeat infection is higher. Keeping your dog on a healthy diet helps to support the immune system and can reduce the chances that the bacteria will proliferate. Omega 3 fatty acids, found in salmon and some other fish, are particularly effective. Natural, immune-supportive supplements are also available for dogs. Discuss the best options with your veterinarian.

In order to reduce the risk of bacteria becoming antibiotic resistant, it’s important to give all the prescribed doses of an antibiotic, even if your dog’s symptoms appear to be better. Otherwise, antibiotic resistant bacteria may survive and pass this ability on to the next generation. Hygiene precautions should be taken around infected dogs to avoid spreading resistant bacteria. Humans carrying MRSA should also be careful about infecting dogs. This is especially likely if your dog is a therapy dog, or spends time around hospital patients. Keep your dog on a healthy diet, and bathe him regularly with antiseptic shampoo to reduce the risk of infection.