Skin Cultures in Dogs and Cats

A skin culture involves taking a sample from or of your pet's skin from an area that may concern your veterinarian. The sample is sent to a laboratory to grow bacteria.

In cases where the infection-causing organism is challenging to identify, multiple samples may be collected to try various conditions for growth, such as aerobic (with air), anaerobic (without air), or in other mediums that grow various bacteria well.

This helps determine the cause of skin infections. Once the sample has been grown in the laboratory, tests can be performed to determine which antimicrobial can be used to clear your pet’s infection. This is called antimicrobial susceptibility and resistance testing.

How is a Skin Culture Performed?

Your veterinarian will give you specific instructions on preparation. In most cases, all antibiotics your pet may be taking for other conditions will need to be discontinued for several days before collecting any samples. This includes any ointments, shampoos, mousses, creams, or sprays that contain these medications. You should not clean the affected skin before bringing your pet in, unless instructed to do so. After the skin site has been prepared, your veterinarian will select the best method of collection based on the signs present.

Pustules (small, infected blisters) are typically drained with a needle, and the material inside is collected with a culture swab. If bleeding or oozing occurs, it should be mild.

For crusted areas, a needle or blade may be used to lift the crust from the skin for collection. The skin underneath may ooze a bit, but that is expected. Keep the area clean and contact your veterinarian if the condition appears to be worsening.

For larger, draining, or deep infections, a punch biopsy is often done. Typically, your pet will be sedated so a thick, round sample can be collected. Depending on the amount of skin removed, stitches may be used to close the wound.

Why Would Your Veterinarian Want a Skin Culture?

A skin culture allows your veterinarian to identify the organisms present and may help determine the cause of the infection. This information helps your veterinarian prescribe the correct medications for your pet’s particular skin issue.

Additionally, some bacteria may be able to spread to you or other pets in the household. If your veterinarian suspects that these bacteria are present, it is even more important to have a culture done to assess the risk to other family members.

Antimicrobial and susceptibility testing are often performed to select the most effective treatment, as many bacteria known to cause skin infections are resistant to several types of antibiotics. This can help create shorter treatment times and lower expense compared to trialing different antibiotics to see if they clear the infection, as well as decrease the risk of creating more antibiotic resistance. Additionally, antibiotics are known to damage the natural gastrointestinal and skin microbiomes, so your pet needs to minimize unnecessary use of them whenever possible.

Testing isn’t needed for all skin infections, but your veterinarian may offer it in more challenging cases. Superficial infections can often be treated with topical medications alone; however, a culture should be performed before initiating oral antibiotics. Other instances where a skin culture may be useful include chronic skin infections, infections that aren’t responding to treatment, infections that have been previously treated with multiple antibiotics, or deep infections that carry an increased risk of complications.

What Happens After a Skin Culture is Done?

Depending on the severity of the infection, your veterinarian may initiate treatment with an antimicrobial or topical medication while awaiting the test results. Once the results are received, they may change or add other antimicrobials as needed. Depending on the laboratory, results typically take around one to two weeks to return, but some cultures may grow more slowly than others.

In rare cases, skin cultures can be negative. However, this can still help provide helpful information for your veterinarian, which can help determine how they treat your pet.

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