Urine Cultures

The number of microorganisms that are present in a  properly collected urine sample may indicate the presence of a urinary tract infection.  Urine is typically sterile as it exits the bladder.  However, as it passes through the urethra and out of the body, it flushes out microorganisms and becomes contaminated with the normal microbiota of the genitourinary system.  The majority of UTI's are caused by invasion of the normal flora by way of the urethra.

Materials

Calibrated 1uL loops
TSA with 5% blood agar or TSA plates
Urine collection containers

Student Instructions

Collect a clean catch, midstream sample of urine in the container provided.

Using  the disposable 0.001 calibrated loop, inoculate a plate with a straight line of urine down the center of the plate.

Carefully spread the urine over the surface of the plate with your metal inoculating loop using a zig-zag pattern.

Incubate for 48 hours.

Count the number of colonies on the plate.  Multiply by 1,000 to convert to numbers per milliliter.  Report in colony-forming units/ml or CFU's/ml

       < 10,000 CFU =  no work up unless it is a specimen from surgery or a catherized specimen.

        > 10,000 CFU buy < 100,000 CFU =  work up organisms with susceptibility if a gram
         negative rod.    (possible contamination or inadequately refrigerated)

      > 100,000 CFU = indicates significant bacteria.  Work up all organisms with susceptibility.

If 3 or more different colony types on a plate then report as contaminated.

If there is a predominate organism present even is less than 100,000 then usually it will be worked up and a MIC reported.

Main organisms of clinical significance found:  E. coli (the most common cause of UTI), Proteus spp., Pseudomonas, Enterobacter, Citrobacter, Klebsiella, Candida albicans, Streptococcus, and Enterococcus faecalis.