What term describes any microorganism capable of causing disease?

The term that best describes any microorganism capable of causing disease is "Pathogen." A pathogen encompasses bacteria, viruses, fungi, and parasites that can invade hosts and lead to illness. This designation includes not only the microorganisms themselves but also their ability to elicit a harmful response in a host organism.

While "Causative Agent" and "Infectious Agent" are terms that relate closely to pathogens, they often refer to the specific organism responsible for a particular disease or infection and may not encompass the full range of potential disease-causing microorganisms. "Infective Organism" is less commonly used compared to the terms "Pathogen" or "Infectious Agent," making "Pathogen" the most widely accepted terminology for microorganisms causing disease.