Which term refers to a micro-organism that causes disease?

The term that refers to a microorganism causing disease is "pathogen." Pathogens include a variety of microorganisms such as bacteria, viruses, fungi, and parasites that can lead to health complications and illnesses. The defining characteristic of a pathogen is its ability to invade a host and disrupt normal physiological functions, ultimately leading to disease.

In the context of the other terms, "aerobe" refers to microorganisms that require oxygen for growth, while "anaerobe" denotes those that thrive in environments devoid of oxygen. These terms describe the oxygen requirements of specific microorganisms but do not inherently relate to disease causation. "Bacteriostatic" refers to substances that inhibit the growth and reproduction of bacteria without necessarily killing them, so it pertains to a method of controlling bacterial growth rather than identifying the organism itself as a disease-causing agent. Thus, "pathogen" is the most accurate term in this context.