Malignant otitis externa is caused by –
**Core Concept**
Malignant otitis externa is a severe infection of the external auditory canal, often seen in immunocompromised patients, particularly those with diabetes mellitus. It is characterized by the rapid progression of infection, involving the cartilage and bone of the external auditory canal, and is typically caused by bacterial pathogens.
**Why the Correct Answer is Right**
Malignant otitis externa is primarily caused by Pseudomonas aeruginosa, a gram-negative rod bacterium. The infection begins as a superficial infection but rapidly progresses to involve the deeper structures of the external auditory canal, including the cartilage and bone. This is due to the virulence factors of Pseudomonas aeruginosa, including its ability to produce exotoxins and elastase, which facilitate its invasion and colonization of the deeper tissues.
**Why Each Wrong Option is Incorrect**
**Option A:** Staphylococcus aureus is a common cause of skin and soft tissue infections, but it is not typically associated with malignant otitis externa.
**Option B:** Escherichia coli is a gram-negative rod bacterium that can cause urinary tract infections and other types of infections, but it is not the primary cause of malignant otitis externa.
**Option C:** Group A beta-hemolytic Streptococcus (GABHS) is a common cause of pharyngitis and skin infections, but it is not typically associated with malignant otitis externa.
**Clinical Pearl / High-Yield Fact**
Malignant otitis externa is a medical emergency that requires prompt treatment with broad-spectrum antibiotics, including coverage for Pseudomonas aeruginosa. It is essential to consider this diagnosis in any patient with severe otalgia, otorrhea, or signs of systemic infection.
**Correct Answer:** D. Pseudomonas aeruginosa