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Urinary Tract Infections

Today, we will continue talking about urine, but we will talk about urinary tract infections, which are some of the most common infections that we see in veterinary medicine.

Canine Urinary Tract

The urinary tract consists of the kidneys, ureters (tubes that carry urine from the kidneys to the bladder), bladder (muscular storage receptacle), and urethra (carries urine outside the body). A urinary tract infection (UTI) can involve any of these areas, and typically, when we talk about UTIs, we mean bladder infection. If the infection ascends into the kidneys, we refer to it as a pyelonephritis. Cats can develop a condition of severe inflammation in the bladder without infection, and this can be erroneously termed a UTI when it is more appropriately termed feline idiopathic cystitis or feline lower urinary tract disease.

Urine is made by filtering waste products from the blood in the kidneys. The urine then passes through the ureters into the bladder where it is stored until the bladder contracts and empties under voluntary control (involuntary leakage is a topic for another day). The bladder does not normally contain bacteria, and the urine should be sterile. Bacteria normally live in the lower urogenital area, and if these bacteria ascend into the bladder, our pets will develop a UTI. Typically, the clinical signs of a bladder infection include frequent urination, straining to urinate, being unable to hold urine/having accidents, or having blood in the urine. Occasionally, pets will drink excessively. Some pets will be completely asymptomatic. With a pyelonephritis, our pets are often sick, running fevers, having elevated white blood cell counts, or experiencing pain over their kidneys.

A urinalysis should be performed to screen for UTIs, and if you missed the last blog, we talked about the information that we learn from a urinalysis. A urine culture should also be performed. With this test, a sample of urine is placed on a special plate that allows bacteria to grow, and they will usually grow in 48 – 72 hours. If growth is seen, the bacteria are transferred to a different plate, and antibiotic discs are placed on the plate. If an antibiotic is effective against the organism, a clear area will be seen around the disc. The lab then measures the space, and the ones with larger kill zones are the ones that will work most effectively to treat the infection and kill the organism. This is known as antibiotic sensitivity or susceptibility.

MacConkey Agar Plate

The most common organism isolated in UTIs is Escherichia coli, and it accounts for 33 – 50% of all infections. The next most common organisms are Staphylococcus spp. and Streptococcus spp., and these account for 25 – 30% of all infections. The remaining 25 – 30% of bacterial isolates include Proteus spp., Klebsiella spp., Enterobacter spp., and Pseudomonas spp.

For an uncomplicated UTI, we want to treat for 10 – 14 days with a narrow spectrum antibiotic, and the most frequent antibiotics used include amoxicillin, Clavamox®, or trimethoprim-sulfa. For complicated UTIs (often seen in patients with immunosuppressive diseases like diabetes mellitus, Cushing’s disease, or cancer), we often treat for 3 – 6 weeks, and the antibiotic used will be chosen based upon culture results. If our pets have recurrent infections, we may even continue antibiotics nightly at reduced dosages for months.

Urine culture sensitivity

urine culture sensitivity diagram

Typically, I recommend a recheck urine culture approximately 5 days after completing antibiotics to ensure that the infection has resolved. Some veterinarians do not repeat the culture if the pet has become asymptomatic again.


In addition to long-term, nightly antibiotics, several other therapies exist to try to prevent UTIs. Cranberries and cranberry extracts prevent certain strains of E. coli from being able to adhere to the bladder walls, and these can be beneficial in some dogs. Probiotics populate the GI tract with “good” bacteria and stimulate gut immunity. In theory, this can then stimulate the overall immune system, decreasing the risk of UTIs. Several probiotics are available, and my favorite is Visbiome®. This particular product was developed for people with Crohn’s disease. D-mannose is a sugar that can prevent bacterial adherence, and it may benefit some pets. Estrogens may even be used in some female dogs to increase epithelial turnover in the vagina, keeping bacterial counts down.

Ultimately, if you are concerned that your pet may be experiencing a UTI, take him (or her) to her primary veterinarian for a urinalysis and urine culture. You will feel better for it, and, more importantly, so will your pet!


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