Middle Ear Mayhem
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/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.
A wealthy alumnus has brought her child to your clinic. Apparently her child attends daycare where there has 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.
INSTRUCTIONS: We have developed a series of questions for you to answer as you go through this case study. Download and print a copy of the WORKSHEET.
RESOURCES:
Background Information:
Methods:
Pathogen Library:
THE DISEASE:
From your knowledge of middle ear infections, you know that most bacterial ear infections are caused by either:
Haemophilus influenzae
Streptococcus pneumoniae
Moraxella catarrhalis.
The question is– what is causing the outbreak, and why aren’t antibiotics working?
THE CAUSATIVE AGENT:
You obtain samples of the middle ear fluid from 3 children who have been treated with oral 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 (selecting for Haemophilus),
5% sheep blood agar plate supplemented with gentamicin (selecting for Streptococcus)
5% sheep blood agar plate supplemented with acetazolamide (selecting for Moraxella).
and incubate at 37ºC for 24 hours. The results are shown below, with positive control plates inoculated with Haemophilus, Streptococcus and Moraxella, respectively.
Review the media reference above. How do each of these media work? What do these results tell you?
THE TREATMENT:
Now that you know which bacterium is causing the otitis media outbreak, you next look at the treatments that have been given. Amoxicillin is typically used for these infections, but you suspect that the concentration prescribed may not be appropriate. Therefore, you run a Minimum Inhibitory Concentration (MIC) assay on the primary isolate by preparing nutrient broths with different concentrations of amoxicillin and inoculating them with the primary isolate.
Review about MIC's in the methods reference above. How do you interpret a MIC result?
You incubate the tubes at 37°C for 24 hours and get the following results:
DFA & MICROSCOPY:
Despite the results from the MIC experiment, the treatment is not working.
You remember reading a paper (see “Chronic Infections” in the Background Info) 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 in the references above.
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. You results are shown below.
CONCLUSION:
You have to figure out what to report back to the alumnus.
Use the results and the information provided to answer the questions and write a conclusion.
For your conclusion, summarize your results using the information from the questions above.
–What caused the otitis media outbreak?
–Why wasn’t the Amoxicillin effective?
–What would you now recommend to your benefactor?
Your answers should be thoughtful and well-organized, and it must incorporate the results you obtained in this case study. That is, use the information from your results and in the references to support your final conclusion.