Why Are There Bacteria In My Dog Or Cat’s Urine?
Ron Hines DVM PhD
Bacteria In Your Pet’s Urine = bacteriuria
Urine, when it is still in your dog or cat’s bladder, should be free of harmful bacteria – but not necessarily all bacteria. (read here) There are two ways of obtaining uncontaminated urine samples from dogs and cats: catheterizing your pet or passing a needle through its tummy wall and into its bladder (cystocentesis). Most vets prefer cystocentesis – particularly if your pet is female. Urine collected by a “clean catch” or from a litter box will always have a few contaminating bacteria that are not clinically relevant. They were picked up from the surrounding skin, urethra, penis or vagina. “Clean catch” urine is fine for all laboratory tests except bacterial culture or deciding if your pet actually has a UTI. The presence of white blood cells in your pet’s urine is a much better indication of a urinary tract infection that needs antibiotic treatment. Even more so if the urine specimen is nitrite positive. Blood-positive urine obtained by clean catch also denotes a problem. But blood in specimens collected by cystocentesis can be due to hypodermic needle trauma. Contrary to what many people believe, there are resident bacteria in the urinary tract that pose no health threats and do not require antibiotic therapy. Some of them are actually beneficial (read here)
The results can be imprecise if your pet’s urine sample was sent to a central veterinary laboratory to identify the species of bacteria it contained and determine which antibiotics are most effective in destroying them. If no bacteria grew at the lab, bacteria may still be present. Urine constituents change rapidly after collection and during shipment. If several different types of bacteria were present in the original sample, the most “vigorous” type often outgrows and masks the others. So, occasionally, infections are missed or falsely reported as positive. That is why pets showing typical UTI signs – particularly when other urine tests indicate a possible infection – generally go on antibiotics regardless of urine culture results.
Conditions That Cause Harmful Bacteria To Be Present In Your Pet’s Urine:
Early Age Neutering: Female pets, particularly those that were neutered before urinary tract maturity are more prone to simple urinary tract infections (simple UTIs). (read here). Pediatric neutering also leads to obesity – another increase in susceptibility to urinary tract infections. (read here, here, here & here)
Feline Urological Syndrome: Cats suffering from feline urological syndrome/FUS occasionally have bacteria in their urine. But those bacteria are not the root cause of their problem.
Bladder And Kidney Stones: Oxalate or Struvite urinary tract stones predispose dogs and cats to repeated urinary tract infections. Bacteria “hide” from your pet’s immune defense cells (e.g. macrophages) in these porous calculi. Only removal of those stones and taking steps to prevent their reoccurrence is a long-term solution.
Stopping Treatment Too Soon: Discontinuing antibiotic treatment too soon, inappropriate antibiotics or those given at too low a dose also predispose pets to repeat infections.
Endocrine Gland Issues: Cushing’s disease, hypothyroidism and diabetes (in dogs and in cats) can make them more susceptible to urinary tract infections.
Birth Defects: It is quite uncommon, but occasional pets are born with structural defects in their urinary tracts (congenital defects) that make them more susceptible to urinary tract infection (urachal diverticulum, ureteral defects, misplaced ureter, etc.).
Trauma: Dogs and cats that have had their spinal cords injured in accidents (neurogenic bladder) or Manx cats that are too severely tailless are very susceptible to urinary tract infections.
Old Age: Aging dogs and cats with weakened urinary sphincter muscles are more prone to urinary tract infection.
Traditionally, veterinarians and physicians believed that urine collected by cystocentesis should never contain any bacteria. However, some of the extremely fragile and difficult-to-identify bacterial inhabitants of the urinary tract might actually be beneficial. (read here)
Complementary Tests:
Complete urinalysis results including the number of Urine WBCs present. The presence of urine nitrite as an indication of the presence of certain bacteria. Your pet’s urine’s pH, Bacterial isolation and antibiotic sensitivity testing. X-rays if urinary tract stones suspected (here & here). Cystoscopy, IVP, Laparoscopy
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