Pathogens and Infection

Pathogens are microorganisms that cause disease and include various species of bacteria, viruses, protozoa and fungi, although not all microorganisms cause disease. Pathogens can cause disease in animals and plants, although the human body has some natural defences that can protect against some of these pathogens.   Infection is nothing but disease acquired by a healthy human being through any means (by touching an object or infected person, through inhaling air containing germs or bacteria of diseases or through body fluid that contains such germs, viruses, parasites or bacteria which cause disease in a healthy human being).   We're all exposed to micro-organisms, and we all get infections from time to time, but that doesn't explain why some people in a certain place develop an infection, while others in the same place at the same time don't.
Bacteria can be classed a living cells as they have the characteristics required to be classed as life form.   The cell structure of bacteria is a single celled prokaryote (meaning no nucleus in its cell) and its size can range from 0.2 to 2 micrometres. Most bacteria have an outer, rigid cell wall. This provides shape and support.   In the cytoplasm are ribosomes and nuclear material which carry genes that control resistance to drugs. Some bacteria have long, whip-like structures called flagella and its main function is movement.   Bacterial cells can multiply successfully and transfer genetic information from an old cell to a new cell.  
Bacteria can be found everywhere, in animals and plants, inside and outside of the body.   Most bacteria found are harmless and useful for making yogurts and cheese.   Gut bacteria found inside of the human body helps with the digestion process by destroying harmful bacteria that enters the human body.   Helpful bacteria are also used to purify water at sewage treatment plants.   It is estimated that only 1 % of bacteria is harmful.
Cholera, Tuberculosis, and Tetanus are all...