Homework answers / question archive / LAB 12: MIDDLE EAR MAYHEM problem-based learning via case study INTRODUCTION You are an intern at a pediatric clinic where you notice that many of the children coming into the clinic have reoccurring ear infections

LAB 12: MIDDLE EAR MAYHEM problem-based learning via case study INTRODUCTION You are an intern at a pediatric clinic where you notice that many of the children coming into the clinic have reoccurring ear infections

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LAB 12: MIDDLE EAR MAYHEM

problem-based learning via case study

INTRODUCTION

You are an intern at a pediatric clinic where you notice that many of the children coming into the clinic have reoccurring ear infections. Some research on your part reveals that 25% of physician visits by children under 3 are due to otitis media, infection of the middle ear.  This amounts to over 25 million cases per year across the US!

Because of the general increase in the resistance of bacteria to antibiotics the current CDC policy is to let these infections clear up on their own.  The bad news is that in about 20% of these cases, the infection persists and reoccurs.

Mrs. Patterson, a wealthy resident of your town, brought her child to your clinic.  Apparently, her child attends daycare where there have been a number of otitis media cases.  She has established a foundation for medical research and has given you a grant to investigate these persistent otitis media outbreaks.

THE DISEASE

From your knowledge of middle ear infections, you know that most bacterial ear infections are caused by Haemophilus influenzae, Streptococcus pneumoniae, or Moraxella catarrhails.  Click on Bacteria Library to review more information about these three pathogens.

 

QUESTIONS

1.  Based on the information you have so far, what is the problem in this case study?

2. Provide three different approaches to solving this problem.  (example: parent, doctor, CDC, etc.)

3.  Evaluate each of the solutions you provided in Question 2 with respect to feasibility, cost, access to resources, and their potential to impact the problem in this scenario.

THE CAUSATIVE AGENT

You obtain samples of the middle ear fluid from three children who have been treated with the antibiotic Amoxicillin, but still have persistent infections.  You streak some fluid from each sample onto agar plates with various growth media:

• chocolate agar supplemented with vancomycin (selects for Haemophilus),
•  5% sheep blood agar plate supplemented with gentamicin (selects for Streptococcus)
• 5% sheep blood agar plate supplemented with acetazolamide (selects for Moraxella).

Plates were incubated at 37ºC for 24 hours. The results are shown in the chart below, with positive control plates inoculated with Haemophilus, Streptococcus and Moraxella, respectively.

Read about selective media at this link to learn more.

QUESTIONS

4.  What does it mean for a medium to be selective?

5. Based on the results of the chart above, which pathogen is the case of infection for each patient? 

DFA & Microscopy

Still, the treatment is not working.   You remember reading a paper (see Chronic Infections) that suggested that biofilms may play a role in recurring ear infections. You decide to go back to the original 3 middle ear samples and observe them under the microscope using the Direct Fluorescent Antibody (DFA) assay, with an antibody specific to the otitis-causing bacterium.

Read about biofilms and the DFA assay to learn more.

As a control, you observe a pure culture of the presumed pathogen, as well as a sample from the middle ear of a healthy child. Your results are shown below.

QUESTIONS

6.  Briefly describe the DFA method.  How does it allow for scientists to look specifically at one kind of bacterium even if there are multiple species within a sample?

7.  What are some drawbacks or disadvantages to the DFA method?

CONCLUSION

Now it’s up to you! You have to figure out what to report back to Mrs. Patterson. For your conclusion, summarize your results of the case study using the following questions:

QUESTIONS

8: What caused the otitis media outbreak? Review the results of selective media and DFA assays to support your answer.

9:  Why was the treatment with amoxicillin not effective?

10: What would you now recommend to your benefactor? Could one of the solutions you proposed in Q2 worked more effectively? What follow up steps, or further work would you recommend?

Lab Adapted from:

• Case Studies in Microscopy, Cornell University 2003. URL:  https://courses.cit.cornell.edu/biomi290/microscopycases/
• Microbiology Laboratory Fundamentals and Applications (2nd ed.) George Wistreich. Pearson Education, Inc., Upper Saddle River, New Jersey
• Carolina Biological Supply. Bacterial Inhibition Lab Kit.