Question

How do you determine the colony count of the urine specimen?

a) Count the number of different bacterial species present.
b) Use a spectrophotometer.
c) Count the number of colonies grown on a culture plate.
d) Measure the volume of the specimen.

Answer 1

To determine the colony count of a urine specimen, microbiologists a. count the number of colonies on an agar culture plate, with each colony representing a colony-forming unit (CFU).

Step-by-step explanation:

To determine the colony count of a urine specimen, option (c) - Count the number of colonies grown on a culture plate - is the accurate method. In microbiology, this is referred to as a total plate count or viable count. A sample of the urine is spread onto a solid agar plate and incubated, allowing the bacterial colonies to grow. After a specified period, colonies that have formed on the plate are counted. Each colony represents a colony-forming unit (CFU), which is presumed to arise from a single or a group of bacterial cells. To ensure accuracy, typically only plates with 30-300 colonies are considered for counting. This range minimizes the occurrence of multiple cells forming a single colony and provides a statistically reliable number close to the true number of living bacteria in the original specimen.

There are other methods like using a spectrophotometer for indirect cell counts based on turbidity, however, for urine specimens specifically, counting colony forming units directly on an agar plate is standard procedure.