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Microbiology Case Study: Case Study

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1. Based on the direct Gram's stain what is the quality of this sputum specimen? Is this specimen of acceptable quality to provide clinically relevant information?

2. Based on the colony morphology and gram stain, what organism is suspect as the cause of Patrick's pneumonia?

3. What type of hemolysis is described by the term "greening" of the medium?

4. What other (nonpathogenic) organisms commonly found in this type of specimen also cause this type of hemolysis?

5. What laboratory test are useful in differentiating these organisms and identifying the pathogens? List at least two tests and be sure to include expected reactions for each organism.

6. Organisms other than the predominant organism were seen in the Gram's stain and culture. Does this mean that the patient has a polymicrobial pneumonia? Why or why not?

7. Should antimicrobial susceptibility testing be performed on this pathogen?

8. What virulence factor does the pathogen possess that can help it evade the hosts defense mechanisms?

9. What preventative measures can be used to prevent infection or reinfection with this pathogen?

10. In this case, the symptoms were quite diagnosistic of pneumonia. Why were urine and blood cultures also collected?

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1.
The quality of this specimen is very good.
Yes, generally an acceptable sputum specimen will consist of many PMN's or neutrophils, and <25 epithelial cells per low power field.

2.
Streptococcus pneumoniae

3.
Alpha hemolysis

4.
Viridans streptococci
Staphylococcus epidermis - note may appear more gamma hemolytic (no hemolysis) than alpha on blood agar plates

5.
Viridans streptococci can be differentiated from Streptococcus pneumoniae using an optochin test, as Viridans streptococci are optochin ...

Solution Summary

This solution contains a case study of an older man with a long history of smoking, presenting to his local ER with respiratory distress. Laboratory analysis of sputum identifies Streptococcus pneumoniae as the infectious agent causing the pneumonia. In this case study colony morphology, and gram stain of S. pneumoniae are discussed. Additionally testing to differentiate closely related Streptococcus species are also discussed in detail. Virulence factors of S. pneumoniae and preventable measures are also included in this solution.

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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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