Microorganisms, Bacteria, Viruses & Protozoa

Microorganisms and Microbes

A microorganism or microbe, also called a microscopic organism, is a living being that can only be viewed with a microscope. They are presented, unlike plants and animals, as a basic biological organization. Most are unicellular, although some are multinucleate or even multicellular. Within single-celled organisms there are prokaryotes, such as bacteria, and eukaryotes, such as protozoa, some algae and fungi, and even ultramicroscopic entities such as the virus. The microbes have multiple shapes and sizes. If a virus were the size of a tennis ball, a bacterium would be the size of half a tennis court and a eukaryotic cell would be like a whole football stadium.

Types of Microorganisms

Bacteria are organisms of a single cell. Their shape can be spherical, spiral, etc. They can exist as individual organisms, forming chains, groups or pairs. Bacteria are the most abundant life forms on Earth. They have a length between 0.4 and 14 µm and a width from 0.2 to 12 µm. Consequently, you can only see them through a microscope. Bacteria reproduce through DNA replication and division into two independent cells. Normally this process takes 15 to 30 minutes.

Viruses

Viruses are ultramicroscopic biological systems (can only be observed with an electron microscope) that can cause infections and that only reproduce in host cells. Viruses outside host cells are in an inactive form. Viruses are characterized by a protective layer; their shape can be spiral, spherical, or other forms, and they have a small size between 0.009 and 0.02 µm. Because they are smaller than bacteria, they can pass through filters that retain bacteria.

Protozoan Parasites

Protozoan parasites are unicellular organisms. They are characterized by a complex metabolism. They feed on solid nutrients, algae, and bacteria present in multicellular organisms, like humans and animals. They are often in the form of cysts or eggs. For example, eggs of Cryptosporidium and Giardia cysts are common in waters affected by fecal contamination.

Classes of Microorganisms

They can be classified into six major groups according to the type of organisms they affect:

• Phytophagous: when they attack plants, causing multiple diseases.
• Soófagos: when they attack animals.
• Dermatropos: affect the skin (e.g., smallpox, herpes, measles).
• Neurotropic: affect the nervous system.
• Respiratory: affect the respiratory system (e.g., influenza, pneumonitis).
• Viscerotropic: attacking various viscera (e.g., viral hepatitis).
• Bacteriophages: when they attack bacterial cultures; this latter category is of great interest because it has allowed a series of experiments that led to the elucidation of many unknowns in the field of molecular genetics.