Bacteria are a Kingdom of prokaryotes, the earliest type of life on earth. Bacteria can be traced back billions of years, and there are an unknown, but massive, amount of bacteria on the planet today. The unifying quality of all bacteria is that they are single-celled micro-organisms, and the vast majority are so small they can only be viewed under a microscope, although there are a rare few that can just barely be seen with the naked eye.

The majority of bacteria are not harmful bacteria, and are known as nonpathogenic bacteria, comprising more than two-thirds of all the bacteria on earth. Nonpathogenic bacteria are found on and in everything, from skin, to water, to our stomachs. Nonpathogenic bacteria actually are necessary to the healthy functioning of any life form, assisting with vital functions like digestion. Nonpathogenic bacteria are constantly moving through our systems, and cause no harm, except in very rare circumstances.

Harmful bacteria, however, known as pathogenic bacteria, can cause incredible damage to our bodies, including death. The term pathogenic means disease carrying, and these harmful bacteria are often referred to simply as germs. They are generally classified based on their shape, with three main groupings: coccus, bacillus, and spirillium. The cocci can be further sub-divided into three groups: streptococci, diplococci, and staphylococci.

Each of these three main groupings of harmful bacteria are associated with their own set of symptoms and ailments. The cocci, for example, produce pus and grow in larger groupings. Cocci cause all sorts of pustules and boils in the body, and so are quite distinctive when they infect a wound or region of flesh. Bacilli are responsible for a number of much more serious diseases, most notably tuberculosis and influenza. Spirilla cause other serious diseases, including syphilis.

As single-celled organisms, harmful bacteria are able to reproduce quite rapidly. Through a process called mitosis, these bacteria split into two identical copies of themselves. These copies can then further split into two more copies, and so on, quickly enlarging a population to staggering numbers. An average bacterium can, within a twenty-four hour period, create many millions of copies of itself, overrunning an organism. Bacteria’s ability to reproduce on its own is one of the key differences between harmful bacteria and harmful viruses. Viruses are also pathogenic, but as they are much, much smaller than bacteria, they need some sort of a host to reproduce, making them slower and more awkward at reproduction.

There are many types of harmful bacteria, some of which are absolutely deadly, while others only cause minor illness. One of the most dangerous harmful bacteria is botulism which can be found in food and can cause death even in incredibly small amounts. Another is yersinia pestis, which caused the bubonic plague, and which still afflicts small portions of the world’s population. A less-dangerous, but still inconvenient, form of harmful bacteria is campylobacter, which is responsible for most cases of food poisoning, causing severe intestinal discomfort and often vomiting. Other bacteria may be an inconvenience if treated, but deadly if left on their own, such as different types of streptococcus, responsible for strep throat and pneumonia.