**Core Concept**
The presence of sulphur granules discharging from a sinus is a classic clinical sign of a specific type of bacterial infection. This condition is characterized by the formation of a granulomatous reaction in response to the bacteria, which leads to the production of these characteristic granules.

**Why the Correct Answer is Right**
The correct answer is related to the bacterium Actinomyces, which is a Gram-positive, filamentous bacterium that can cause actinomycosis. This infection typically occurs in the face and neck region, and the presence of sulphur granules is a hallmark of the disease. The bacteria invade the tissues and cause a granulomatous reaction, leading to the formation of these characteristic granules. The granules are composed of bacterial filaments that are surrounded by a thick, yellowish capsule, which gives them a characteristic appearance.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the presence of sulphur granules is not typically associated with Staphylococcus aureus infections. While S. aureus can cause a variety of skin and soft tissue infections, it is not characteristically associated with the formation of sulphur granules.

**Option B:** This option is incorrect because the presence of sulphur granules is not typically associated with Aspergillus infections. While Aspergillus can cause a variety of fungal infections, it does not typically cause the formation of sulphur granules.

**Option C:** This option is incorrect because the presence of sulphur granules is not typically associated with Nocardia infections. While Nocardia can cause a variety of bacterial infections, it is not characteristically associated with the formation of sulphur granules.

**Clinical Pearl / High-Yield Fact**
The presence of sulphur granules is a classic clinical sign of actinomycosis, and it is often associated with a history of dental procedures or trauma to the face and neck region. Remember that actinomycosis is a chronic infection that can cause significant morbidity if left untreated.

**Correct Answer:** D. Actinomyces.