A patient has a brain abscess. The aspirated material is foul smelling and shows red fluorescence under ultraviolet light. Which organism could be implicated?

Question

Image below highlights jugular foramen. Which of the following structures do not pass through the marked structure “A”?

Answer 1

The question gives two lab clues for a brain abscess: a bad smell on aspiration, and red fluorescence when the pus is checked under UV light.

Staphylococcus aureus: A common cause of brain abscess, but its pus is not foul smelling and shows no red fluorescence, so it does not fit either clue.
Peptostreptococcus: An anaerobe that can produce foul smelling pus, matching the first clue, but it lacks the pigment that causes red fluorescence, so the second clue is missed.
Bacteroides: An anaerobe that produces foul smelling pus, and the pigmented strains (once grouped as Bacteroides melaninogenicus) glow brick red under UV light. Both clues line up.
Acanthamoeba: A free living amoeba linked to chronic granulomatous brain infection and keratitis, not a foul smelling pyogenic abscess, and it has no fluorescence property.

Only Bacteroides accounts for both the smell and the UV fluorescence together, so it is the organism implicated here.

Let's summarize:

Foul smelling pus points to anaerobic infection.
Red fluorescence under UV light is specific for pigmented Bacteroides species.
Staphylococcus aureus, Peptostreptococcus and Acanthamoeba do not explain both features together.

The organism implicated is Bacteroides.

Answer 2

The question gives two lab clues for a brain abscess: a bad smell on aspiration, and red fluorescence when the pus is checked under UV light.

Staphylococcus aureus: A common cause of brain abscess, but its pus is not foul smelling and shows no red fluorescence, so it does not fit either clue.
Peptostreptococcus: An anaerobe that can produce foul smelling pus, matching the first clue, but it lacks the pigment that causes red fluorescence, so the second clue is missed.
Bacteroides: An anaerobe that produces foul smelling pus, and the pigmented strains (once grouped as Bacteroides melaninogenicus) glow brick red under UV light. Both clues line up.
Acanthamoeba: A free living amoeba linked to chronic granulomatous brain infection and keratitis, not a foul smelling pyogenic abscess, and it has no fluorescence property.

Only Bacteroides accounts for both the smell and the UV fluorescence together, so it is the organism implicated here.

Let's summarize:

Foul smelling pus points to anaerobic infection.
Red fluorescence under UV light is specific for pigmented Bacteroides species.
Staphylococcus aureus, Peptostreptococcus and Acanthamoeba do not explain both features together.

The organism implicated is Bacteroides.

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