What type of microorganisms cause infections?

Pathogenic microbes are the correct answer because they are specifically defined as microorganisms that can cause disease in a host. These include bacteria, viruses, fungi, and parasites that have the ability to invade tissues, evade the immune system, and multiply, leading to infection and illness. Their virulence factors can facilitate their ability to cause harm, such as toxins or the ability to adhere to host cells.

In contrast, non-pathogenic microbes typically do not cause disease and can even play beneficial roles in processes like digestion or maintaining a healthy microbiome. Beneficial microbes, as the term suggests, are organisms that provide health benefits, such as probiotics. Environmental microbes refer to those found in various ecosystems and are essential for nutrient cycling and other ecological functions, but they do not inherently cause infections. Thus, they do not fit the definition of microorganisms that cause infections, making pathogenic microbes the clear choice.