A vitreous aspirate from a case of metastatic endophthalmitis on culture yields Gram-positive round to oval cells, 12-14 mm in size. The aspirate on Gram staining shows the presence of pseudohyphae. Which of the following is the most likely aetiological agent?
**Core Concept**
Metastatic endophthalmitis is an intraocular infection that spreads from a distant site, often through the bloodstream. This condition is commonly associated with fungal infections, particularly in immunocompromised patients. The presence of pseudohyphae on Gram staining is a key diagnostic feature of certain fungal pathogens.
**Why the Correct Answer is Right**
The presence of pseudohyphae and Gram-positive round to oval cells, 12-14 mm in size, is characteristic of Candida species, particularly Candida albicans. Candida albicans is a common cause of endophthalmitis, especially in cases of metastatic infection. The organism's ability to form pseudohyphae and exhibit a "saucer-cup" effect on cornmeal agar is a distinctive feature. Furthermore, Candida albicans is known to produce biofilms, which can contribute to its pathogenicity in endophthalmitis.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Aspergillus species are typically seen in endophthalmitis as branching hyphae, not pseudohyphae. Aspergillus species are also more commonly associated with allergic reactions and asthma.
* **Option B:** This option is incorrect because Staphylococcus aureus is a Gram-positive coccus, not a round to oval cell. Additionally, S. aureus is more commonly associated with endogenous endophthalmitis, particularly in cases of ocular trauma or surgery.
* **Option D:** This option is incorrect because Nocardia species are typically seen as partially acid-fast, branching rods, not pseudohyphae. Nocardia species are also more commonly associated with subacute or chronic infections, particularly in immunocompromised patients.
**Clinical Pearl / High-Yield Fact**
Candida endophthalmitis is a medical emergency that requires prompt treatment with intravitreal antifungal agents, such as amphotericin B or voriconazole. Early diagnosis and treatment are crucial to prevent vision loss and improve outcomes.
**Correct Answer:** C. Candida albicans