Which theory states that infectious diseases are brought about by certain microbes?

The Germ Theory is the correct answer because it specifically posits that many diseases are caused by microorganisms, including bacteria, viruses, and other pathogens. This theory was developed in the 19th century, marking a significant shift in understanding disease causation, emphasizing that these tiny organisms can infect the body and lead to various illnesses. It laid the foundation for modern microbiology and health practices, including sanitation, vaccination, and antibiotic treatments, ultimately leading to significant improvements in public health.

In contrast, the Miasma Theory, which predates the Germ Theory, suggested that diseases were caused by "bad air" or noxious vapors emanating from decomposing organic matter. The Cell Theory, while fundamental to biology, concerns the composition and function of cells, asserting that all living organisms are made of cells and that cells are the basic unit of life, but it does not specifically address infectious diseases. Virology Theory focuses on viruses as a distinct group of pathogens, but it is more specific than Germ Theory, which encompasses all microbes.