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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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    Solution Preview

    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.

    Streptococcus pneumoniae

    Alpha hemolysis

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

    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.