A patient presents with a frontal abscess. Foul-smelling pus is aspirated. Pus shows red fluorescence on the ultraviolet examination. The most likely organism causing the frontal abscess is
**Core Concept**
The patient's frontal abscess with foul-smelling pus and red fluorescence under ultraviolet examination suggests the presence of a specific type of bacteria that produces a characteristic pigment.
**Why the Correct Answer is Right**
The red fluorescence under ultraviolet examination is indicative of pyoverdin production, a greenish-yellow pigment produced by *Pseudomonas aeruginosa*. This bacterium is known to cause a variety of infections, including abscesses, and is often associated with foul-smelling pus due to the presence of indole. The production of pyoverdin is a key virulence factor for *Pseudomonas aeruginosa*, allowing it to outcompete other bacteria in the environment.
**Why Each Wrong Option is Incorrect**
**Option A:** *Staphylococcus aureus* does not typically produce a pigment that causes red fluorescence under ultraviolet examination, and while it can cause abscesses, the presence of foul-smelling pus and red fluorescence is more suggestive of *Pseudomonas aeruginosa*.
**Option B:** *Escherichia coli* can cause a variety of infections, but it does not typically produce a pigment that causes red fluorescence under ultraviolet examination.
**Option C:** *Klebsiella pneumoniae* can cause abscesses and produce a pigment, but it is not typically associated with the red fluorescence under ultraviolet examination described in this scenario.
**Clinical Pearl / High-Yield Fact**
Foul-smelling pus with red fluorescence under ultraviolet examination should raise suspicion for *Pseudomonas aeruginosa* infection, particularly in immunocompromised patients or those with a history of exposure to contaminated water sources.
**Correct Answer:** C. *Pseudomonas aeruginosa*.