Bacteria are single celled organisms with a diameter of about 0.5-2μm, and the maximum resolution of optical microscopes is about 200nm, so bacteria cannot be directly observed. Using an optical microscope can only observe the characteristics such as color and movement of bacteria, but cannot directly observe the bacteria themselves. If you want to observe bacteria, you can use an electron microscope, which has a higher resolution than an optical microscope and can directly observe the morphology and structure of bacteria.
Under specific conditions, optical microscopes may magnify up to thousands of times, but are still limited by resolution and cannot directly observe bacteria. Because bacteria are too small to distinguish under ordinary optical microscopes.