Viruses are very small and can be considered ultramicroscopic. We were not able to see them with the best light microscopes as we could bacteria (prokaryotes). We have to use an electron microscope to see them as they are that small. This was not available until recently. Leeuwenhoek's microscope was not strong enough to see such small things.
A microbial infection is any infection caused by a microbe, or microorganism. Microbial infections can be caused by viruses, protozoa, bacteria and some fungi.
Microbes are sorted into these 4 groups: Viruses, Fungi, Bacteria and Protozoa
bacteria or viruses, which are capable of causing disease
bacteria or viruses, which are capable of causing disease
Bacteria and viruses
protozoa fungi bacteria viruses prions
Viruses are the smallest microbes known that cause disease. They are sub-microscopic. This means that they can not be seen with a regular microscope because they are too small (measured in nanometers). It takes an electron microscope to see a virus particle. The second microbe that is among the smallest would be bacteria and then probably protists, as a generalization, after that (protists and bacteria have wider ranges of sizes than viruses). Bacteria are microscopic living organisms, while the viruses are non-living sub-microscopic organisms. Protists are single-celled living organisms, such as protozoa.
Scientists have classified microbes into different kingdoms based on their characteristics. The five-kingdom classification system includes the Kingdom Monera, which comprises most microbes like bacteria. However, advancements in microbiology have led to the recognition of additional microbial groups beyond traditional kingdom classifications.
viruses, bacteria, algae, fungi, and protozoa
mould
The three main types of microbes are fungi, bacteria and viruses. Bacteria are usually smaller than fungi and virus is the smallest type of microbe.
It is incorrect to call a virus a microbe because a microbe is a living organism, while a virus is not. Viruses do not exhibit all the characteristics necessary to be classified as a living organism.