Which organism is known to be the primary cause of thrush?

The primary cause of thrush is Candida albicans. This organism is a type of yeast that typically resides in the mouth, digestive tract, and female genital tract without causing harm. However, under certain conditions, such as a weakened immune system, prolonged antibiotic use, or hormonal changes, Candida albicans can overgrow and lead to an infection known as thrush, characterized by white patches in the oral cavity and soreness.

In terms of understanding the other organisms listed, Aspergillus niger is a mold that primarily causes lung infections or systemic infections in immunocompromised individuals but is not associated with thrush. Staphylococcus aureus is a bacterium commonly responsible for skin infections and certain types of food poisoning, but it does not cause thrush. Escherichia coli is a bacterium mainly associated with gastrointestinal issues and urinary tract infections; it is not related to oral candidiasis or thrush.

Thus, Candida albicans is uniquely suited to be the primary causative agent of thrush due to its yeast-like characteristics and ability to proliferate in the oral environment under certain predisposed conditions.