What technological advancement aided Pasteur and Koch in their work?

The advancement that significantly aided Pasteur and Koch in their work was high-powered microscopes. These sophisticated instruments allowed them to observe microorganisms that were previously invisible to the naked eye. This capability was crucial for both scientists in establishing the germ theory of disease, which posits that many diseases are caused by specific microorganisms.

With high-powered microscopes, Pasteur could investigate the causes of fermentation and spoilage, while Koch was able to identify the specific bacteria responsible for diseases such as anthrax and tuberculosis. This technological progress was instrumental in transitioning medicine from theories based on miasma and humors to a more scientific understanding based on microbiology, leading to improved public health measures and the development of vaccines.

Other options such as antibiotics, X-ray machines, and vaccination methods, while significant in their own right, were either developed later or were not foundational in the immediate work of Pasteur and Koch regarding the identification and understanding of germs.