Bacterial Ear Infections In Dogs

Ear problems in dogs are not uncommon. Many normal dog ears will have some bacteria present, but a change in the underlying health of the ear can make this normal flora proliferate, cause disease and can allow other environmental bacteria to invade.

The most common underlying factor leading to bacterial ear infections are allergies, which can cause the skin lining the ear to become inflamed. With inflammation, there is a change in the ear "micro-climate", increasing the temperature and humidity in the ear canal and providing a perfect environment for bacteria to multiply.

Other factors changing the ear environment, such as excess ear wax, a foreign body like a grass seed, ear mites or frequent swimming can also lead to bacterial ear infections.

Dogs with narrow ear canals (like Shar Peis) or floppy ears (spaniels) have an increased likelihood of ear disease because their ear canals are less ventilated. A bacterial ear infection quite commonly occurs simultaneously with a fungal or yeast infection as the factors predisposing to both infections are the same.

The signs of a bacterial infection are similar to those seen with other ear diseases. They include rubbing at the ears, shaking the head, a red and painful ear, a malodorous discharge, tilting the head to one side or hearing loss.

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Owners who see such signs should consult their veterinarian to have the problem correctly diagnosed and treated. The veterinarian will most likely look down the ear with an otoscope to check whether the ear drum is intact. If it is not this will affect the choice of treatment, as many of the topical preparations can potentially cause deafness if they come into contact with the delicate hearing and balance apparatus normally protected by this membrane.

The vet will also probably take an ear swab and examine it under the microscope to identify the type of bacteria or fungi present. The vet may collect a sterile sample to send away to a laboratory to culture the exact bugs and then check which antibiotics are effective in killing them.

There are two main groups of bacteria which can affect the ears, known as "Gram-positive" or "Gram-negative". Bacteria of the same Gram type have a similar cellular structure and are usually susceptable to similar types of antibiotics.

The most common Gram-positive bacteria causing ear disease are Staphylococcus intermedius and Streptococcus spp. These are known as Staphs and Streps, with similar bacteria occuring in human infections. The most common Gram-negative bacteria in ear disease are Pseudomonas spp and Proteus spp. Gram-negative bacteria tend to be more difficult to treat than Gram-positive bacteria, as they are more resistant to common antibiotics.

Depending on the severity of the infections, the veterinarian may suggest medicated ear drops, ear cleaners, oral antibiotics or anti-inflammatories (or a combination of these) to treat the disease. Sometimes it is necessary to anesthetize the dog to properly clean out the ear canal so that a home treatment will be effective. Alternatively, it may be necessary to remove a grass seed or other foreign body from the ear so it can start to heal.

Many ear cleaners have antibacterial properties themselves. The organic acids found in many cleaners, parachlorometaxylenol in Epi-Otic, and Triz-EDTATM (particularly for Gram-negative infections) are all useful adjuncts to prescription ear drops containing more potent antibiotics.

Most cleaners should be introduced into the ear about an hour prior to any medicated drops, to prevent dilution. Triz-EDTATM is an exception to this rule. It should be used only 15 minutes prior to the ear drops, as it will assist the antibiotic to penetrate into the bacteria, improving its effect.

Ear disease can be very frustrating to combat, so ensure you follow all the veterinarian's instructions carefully. Treat the required number of times each day and for the correct length of time to avoid a relapse of the problem. Recurring ear problems can be much more difficult to treat, so getting on top of the problem at the outset is preferable for both the owner and the dog.

Epi-Otic is a registered trademark of Virbac
Triz-EDTA is a registered trademark of DermaPet, Inc, Potomac MD 20854