The concept of significant bacteriuria was introduced to aid differentiation between harmless bacterial contaminants of urine
and pathogenic organisms causing infectious disease of the urinary system. A high bacterial count in a properly collected
and cultured urine sample indicates the high probability of UTI (Table 7). Small numbers of bacteria obtained from untreated
patients usually indicate contamination.
Table 7 Interpretation-quantitative urine cultures in dogs and cats*
The lower limit of numbers of bacteria isolated from feline urine that indicate infection (so-called cutoff values) has not
been precisely determined. However, it is usually less than those in dogs because feline urine appears to be less conducive
to bacterial growth than urine of dogs (Table 7).
Caveat: When interpreting bacterial cultures, several variables should be considered (Table 6). In up to 20 percent of canine patients,
bacterial UTI may be present with less than 10,000 colony-forming units per milliliter of urine. In this circumstance, samples
collected by catheterization or during voiding might erroneously be interpreted as contaminants (Table 7). This observation
emphasizes the importance of cystocentesis as the preferred method of collection for diagnostic urine culture.
Dr. Osborne, a diplomate of the American College of Veterinary Internal Medicine, is professor of medicine in the Department of Small
Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota.