Among microorganisms that are generally referred to as “germs” are four types: bacteria, viruses, fungi, and protozoa. They invade and live in plants, animals, and people, sometimes causing illness in their hosts.
Bacteria are one-celled creatures that gain nourishment from their environment. They can reproduce outside or inside the body and can cause infections such as ear infections, sore throats (tonsillitis, strep throat), and pneumonia.
Viruses must live within living cells to grow and reproduce. Illnesses they cause include chicken pox, measles, and flu.
Fungi get their nutrition from plants, animals, and humans. They usually prefer damp, warm environments and are not usually dangerous to healthy individuals. An example is the athlete’s foot fungus.
Protozoa are one-celled organisms that usually spread through water, such as Giardia lamblia. They usually infect the intestines and may cause diarrhea, nausea, and stomach pain.