Bacteria in a urine specimen may indicate a urinary tract infection. Still, it may also be contaminated if the specimen has been held at room temperature for a prolonged period and/or not collected using a clean-catch protocol. It is essential to perform a urinalysis on a freshly collected midstream specimen to determine the significance of the bacteria that may be seen.
The presence of increased numbers of WBCs is also an indication of urinary tract infection. Bacteria are indicated by the arrows in the image on the right. Several WBCs are also present in this field. In this case, the presence of bacteria most likely indicates a urinary tract infection.
The bacteria appear very dark when phase-contrast microscopy is used, as shown in the bottom image. The larger cells are white blood cells (blue arrow).
