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Anaerobic Bacterial Infections in Dogs

A tired brown dog lies its head down on a brown wood floor

Bacteria are single-celled organisms that exist in a variety of environments, but the most pertinent types of bacteria in medicine are the kind that exists in our bodies and the kind that is pathogenic. Some bacteria can protect us from disease while other types can cause it.

Just like in humans, dogs have naturally-occurring bacteria in their bodies that provide many benefits. These beneficial bacteria can help with food digestion while others block harmful bacteria from accumulating and causing disease. Regardless of their beneficial or harmful properties, all bacteria can be placed into one of two categories: aerobic bacteria and anaerobic bacteria. What does this mean, and what happens if your dog develops an infection from anaerobic bacteria?

What are anaerobic infections in dogs?

Bacteria may beaerobic which means they require oxygen to thrive, and other types of bacteria areanaerobic which means that they can thrive without the presence of oxygen in their environment. Some of these anaerobic bacteria cannot exist in oxygen-rich environments (obligate anaerobes) while others can use small amounts of oxygen as part of their metabolism (facultativeanaerobes). 

It is important to note that not all anaerobic bacteria are bad. Many of these bacteria are competition for bad bacteria in that beneficial bacteria can block bad bacteria from attaching to surfaces on or within the body. They can also inhibit inflammatory responses, and they can activate certain parts of your dog’s immune system. 

Anaerobic bacteria naturally exist in small numbers in your dog’s gastrointestinal tract, in his mouth and gums, and even on the skin in some cases. When there is a break in the skin and anaerobic bacteria are allowed to go deeper, they can thrive in these low-oxygen environments and cause non-healing of bite wounds or abscesses. If inflammation of the digestive tract causes the displacement of beneficial bacteria, disease-causing bacteria can have more room to develop and cause further illness. 

Symptoms of anaerobic bacterial infection in dogs 

Anaerobic infections can look identical to other common infections. For example, they can look like typical dermatitis and cause red or rash-like skin lesions. However, infections that are anaerobic in nature can be very stubborn and difficult to heal, so they may not resolve within just a few days of starting an antibiotic. Anaerobic infections can also cause oozing and pus-like discharge, especially if there is an abscess present.

In the case of anaerobic infections affecting the gastrointestinal tract, your dog may have persistent diarrhea that does not resolve with a simple bland diet or probiotics. In severe cases, anaerobic can lead tosepsis which is a body-wide response to infection that is life-threatening. These pups appear very weak and may also have a fever. They will also have a lack of appetite.

Anaerobic infections can also occur in the urinary bladder. This happens when bacteria migrate up the urogenital tract, from the vagina or penis. Urinary tract infections can cause painful urination, cloudy urine, and frequent urination. You may even notice blood in your dog’s urine over time, and they may also frequently lick their genitals to indicate their discomfort.  

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Causes of anaerobic infections in dogs

Since anaerobic bacteria are a normal part of your dog’s mouth, it is possible to transmit bacteria through a bite wound. Superficial wounds may resolve with typical antimicrobial therapies but deep puncture wounds can be very stubborn. For this reason, culture and sensitivity testing are being more frequently recommended for dogs who go to their vet’s office due to bite wounds.

Since the mouth is a hotbed for these types of bacteria, routine dental cleanings are highly recommended. Deep cleanings around the teeth and below the gums are important because they can remove much of this bacteria and promote the healing of periodontal disease and periodontitis if present. And because this kind of bacteria can be harmful elsewhere in the body, general anesthesia is always recommended for a dental. Otherwise, the bacteria that is aerosolized during the cleaning can be inhaled or swallowed, potentially causing infection elsewhere in the body. And without dental cleanings, harmful bacteria can get into the bloodstream through the gums and make their way to the heart.

All surgeries should be performed using an aseptic or sterile technique to ensure that bacteria do not enter the surgery site. This is also the reason why dogs should wear Elizabethan collars after surgery. Incision sites can be itchy when they heal, and when dogs lick these incisions, they can introduce bacteria into the incision site and cause infection or non-healing of the site. This is especially important with orthopedic surgeries because if infection occurs with implants or devices, additional surgery will be necessary to remove the infected implants!  

Treating anaerobic infections

Anaerobic infections can be very stubborn to treat, and so culture and sensitivity testing are often necessary. By swabbing the area of skin with a sterile cotton-tipped applicator, bacteria can be collected and sent to a lab to see what species of bacteria present and which antibiotic will kill it. The same can be determined by collecting sterile urine samples from the urinary bladder or submitting a fecal sample in cases with persistent diarrhea.

Longer courses of antibiotics are often necessary to resolve these infections, and because antibiotics can be harmful to some of the other beneficial bacteria in the body, it is often necessary to take probiotic supplements to help replenish the good bacteria. Otherwise, vomiting and diarrhea can develop. For wound care, some may need to be surgically debrided in order to remove diseased or necrotic tissue.

Many specialty facilities are also having success with hyperbaric oxygen therapy. This involves the flooding of pressurized oxygen into the body so that obligate anaerobic bacteria can no longer thrive. For body-wide infections and sepsis, hospital care is necessary and usually involves intravenous fluid therapy and injectable antibiotics.

Anaerobic bacteria do have some health benefits, but then they are in the wrong place at the wrong time, they can cause significant infections that are difficult to treat. Testing is important to determine what species of bacteria are present if your dog has a non-healing wound or an infection that isn’t responding to initial therapies.

Meet The Author 

Dr. Erica Irish DVM


Erica has worked in the veterinary field since 2006, starting out as a veterinary technician before graduating from the UF College of Veterinary Medicine in 2013. As a general practitioner in an animal hospital, she has many interests and is especially interested in dermatology, cardiology, internal and integrative medicine.

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