Bacteria under the microscope

We all know that there are a lot of bacteria around us, but they are difficult to see with our naked eyes. Therefore, if we want to see bacteria, we usually look at them under a microscope. Today I will introduce to you how we can see bacteria under a microscope? Now let’s take a look with the editor.

The microscope is an optical instrument composed of a lens or a combination of several lenses. It is a symbol of mankind's entry into the atomic age. An instrument mainly used to magnify tiny objects so that they can be seen by the naked eye. Microscopes are divided into optical microscopes and electron microscopes: the optical microscope was first invented by Janssen and his sons in the Netherlands in 1590. Today's optical microscopes can magnify objects 1600 times, with a minimum resolution limit of 0.1 microns. The mechanical tube length of domestic microscopes is generally 160 mm. Among them, the person who made great contributions to the development of microscopes and microbiology was Antonie van Leeuwenhoek, a Dutch citizen.

The microscope is one of the greatest inventions of mankind in this period. Before it was invented, humans' perception of the world around them was limited to what they saw with their naked eyes, or with the help of handheld lenses.

The microscope opened a whole new world to human vision. For the first time, people saw hundreds of "new" tiny animals and plants, as well as the internal structures of everything from the human body to plant fibers. Microscopes also help scientists discover new species and doctors treat diseases.

Viruses are very small. The diameter of most individual virus particles is around 100nm, which means that only when about 100,000 virus particles are lined up can they be barely seen with the naked eye. Viruses are so small that most of them can only be observed with the aid of an electron microscope, which has a resolution 1,000 times that of an optical microscope. The size of different viruses varies greatly. The smallest, such as the Geminiviruses of plants, have a diameter of only 18-20nm, the largest, such as the Poxviruses of animals, are 300-450nm×170-260nm in size, and the longest, such as the Filoviridae virus particles, are 80nm×790-14000nm in size. The resolution distance of an optical microscope is d=0.61λ/NA, where d is the resolution distance of the objective lens, in nm. λ——Wavelength of illumination light, unit: nm. NA - numerical aperture of the objective lens. For example, the numerical aperture of an oil immersion objective lens is 1.25. The wavelength range of visible light is 400-700nm. Taking the average wavelength as 550nm, d=270nm, which is approximately half the wavelength of the illumination light. Generally speaking, the resolution limit of a microscope illuminated with visible light is 0.2μm, or 200nm, which is larger than the diameter of a virus. Therefore, viruses cannot be seen with an optical microscope. Bacteria are much larger than viruses. The diameter of a single coccus is about 0.8 to 1.2 μm. Most bacilli are medium-sized, 2 to 5 μm long and 0.3 to 1 μm wide, which are within the observable range of an optical microscope.

Bacteria are very small, so small that we cannot see them with our naked eyes, but we clever humans invented the microscope so that we can see bacteria. In fact, there are many bacteria in our lives, but many common bacteria are harmless to our bodies so we don’t need to worry.