There are five major groups of micro-organisms:
i. Bacteria – They are single celled disease-causing micro-organisms. They can be spiral or rod- shaped.
ii. Fungi – They are mostly multicellular disease-causing microbes. Bread moulds are common examples of fungi.
iii. Protozoa – They mainly include organisms such as Amoeba, Plasmodium, etc. They can be unicellular or multicellular.
iv. Virus -Viruses are disease-causing microbes that reproduce only inside the host organism.
v. Algae – They include multicellular, photosynthetic organisms such as Spirogyra, Chlamydomonas, etc.