**Core Concept**
Fungal infections in non-HIV (immuno-competent) individuals are typically caused by opportunistic pathogens that take advantage of minor disruptions in the host's immune system. Candidiasis is a common fungal infection in this population, primarily caused by the yeast Candida albicans. This opportunistic pathogen is normally found on the skin and mucous membranes but can cause disease when it overgrows and invades the host tissues.

**Why the Correct Answer is Right**
Candidiasis is the most common fungal infection in non-HIV (immuno-competent) individuals due to the widespread presence of Candida albicans on the skin and mucous membranes. When the host's immune system is compromised, even slightly, Candida can overgrow and cause disease. This can occur in various settings, such as when the skin is broken, in the presence of antibiotics that disrupt the normal bacterial flora, or in cases of diabetes mellitus. The pathogenesis of candidiasis involves the adherence of Candida to the host tissues, followed by the production of biofilms that protect the fungus from the host's immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** Mucor is a type of fungus that causes mucormycosis, a serious and often fatal infection in immunocompromised individuals, particularly those with diabetes or taking corticosteroids. It is not the most common fungal infection in non-HIV (immuno-competent) individuals.
**Option B:** Histoplasmosis is a fungal infection caused by Histoplasma capsulatum, which is typically acquired by inhaling the spores of the fungus. It is more common in immunocompromised individuals and is not the most common fungal infection in non-HIV (immuno-competent) individuals.
**Option C:** Aspergillosis is a fungal infection caused by Aspergillus species, which is typically acquired by inhaling the spores of the fungus. It is more common in immunocompromised individuals and is not the most common fungal infection in non-HIV (immuno-competent) individuals.

**Clinical Pearl / High-Yield Fact**
Candidiasis is often associated with the presence of a central venous catheter, particularly in the context of total parenteral nutrition. This is because the catheter can provide a conduit for Candida to enter the bloodstream and cause disseminated candidiasis.

**✓ Correct Answer: D. Candidiasis**