USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What is the typical causative organism in Malignant Otitis Externa?

1. Streptococcus pneumoniae

2. Pseudomonas aeruginosa

3. Staphylococcus aureus

4. Haemophilus influenzae

The correct answer is: Pseudomonas aeruginosa

Malignant otitis externa is a serious infection that typically occurs in immunocompromised individuals, particularly those with diabetes mellitus. The infection primarily originates in the external auditory canal and can lead to the temporal bone's involvement, potentially causing severe complications. Pseudomonas aeruginosa is the most common organism associated with malignant otitis externa due to its environmental prevalence and its ability to thrive in moist conditions typical of the external ear canal. This opportunistic pathogen is known for its virulence factors that enable it to establish infections in individuals with compromised immunity. Streptococcus pneumoniae is more commonly associated with upper respiratory infections and acute otitis media rather than malignant otitis externa. Staphylococcus aureus, particularly methicillin-resistant Staphylococcus aureus (MRSA), can cause skin and soft tissue infections but is not the primary causative agent of this condition. Haemophilus influenzae is also typically linked to respiratory tract infections and not known for its role in malignant otitis externa. In summary, Pseudomonas aeruginosa is identified as the main causative organism in malignant otitis externa due to its environmental adaptability and the typically compromised immune status of affected individuals. Understanding the pathogen's role helps guide appropriate antibiotic therapy and management