Microorganisms are useful as well as harmful also, in fact, some microbes are very helpful but most of them are harmful to living beings. 1. Some microorganisms are pathogens which cause diseases to human animals and plants.2. Bacteria and fungi are well known to cause food spoilage and make them unfit for eating.3 Bacteria cause some diseases like cholera, typhoid, and diarrhea through water and food.4. Virus scan causes smallpox, cold, hepatitis polio and soon.5. Some microorganisms show antibiotic resistance to certain diseases.