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Microbiology Case Studies

Case Study 1
Shawna was working in a physician office laboratory (POL) when a urine dipstick result
indicated presence of blood and WBCs in the urine she was testing. Laboratory protocol
specified that a urine culture and sensitivity (C & S) should be set up. Shawna obtained a blood
agar plate from stock. On the bottom of the plate she placed the patient's barcode label and
streaked the plate for colony count. She then placed the culture plate into the incubator to be read
the next morning.

1. Was the urine culture set up correctly?
2. Does blood agar support the growth of both gram-positive and gram-negative organisms?

Case Study 2
Tina is a technician in a small hospital laboratory. She works in the hematology, chemistry, and
microbiology sections. On this morning, she was in microbiology examining culture plates that
had been set up the previous day. She examined BA and MAC plates set up for a urine culture.
Both plates had many colonies growing, and the colonies on each plate appeared to have the
same morphology. Tina counted 132 colonies on the MAC plate. From the requisition slip, she
saw that the person who set the culture up had used a 0.001-mL loop. Tina reported a colony
count of 13,200/mL for the culture.

1. Evaluate Tina's performance in evaluating the urine culture.
2. Does the patient have a urinary tract infection?

Critical Thinking problem
Mrs. Miller went to her healthcare provider complaining of frequent, painful urination
accompanied by a burning sensation, symptoms she had never had before. The provider ordered
a routine urinalysis and a urine culture and colony count. In the laboratory, Mrs. Miller gave the
laboratory order to John, who handed her a urine collection cup just as the phone rang. Mrs.
Miller took the cup to the restroom and brought back a urine specimen, with her ID label on the
cup. John set up the urine culture and gave the urine specimen to Timothy, the other technician.
Timothy performed a routine urinalysis including microscopic analysis of the urine sediment and
observed 5 to 10 epithelial cells/low power field, mucus threads, and many bacteria. The next
morning the BA culture plate had at least four different colony types growing on it.

1. Should the laboratory try to identify all four isolates?
2. What mistake(s) affected the routine urinalysis and culture?

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Case 1
1. Yes she did set up the urine culture and sensitivity correctly.
2. Blood Agar supports the growth of both gram ...

Solution Summary

Microbiology Cast studies about urine cultures and CBCs