What are Bacteria?

Bacteria are micro-organisms, i.e. tiny single-celled organisms. They are everywhere from deep in the earth’s crust to surface soils. They thrive in water, can penetrate many solids and can be blown by the wind from one area to another. Many strains are not affected by highly acidic or even radioactive environments. They are the most pervasive form of “life” on Earth, often providing a beneficial function like fixing nitrogen from the atmosphere so that we can breathe what is left.

The major classes of bacteria are gram-positive and gram negative. The bacteria which test positive when the Gram Stain Test is applied include Listeria, Staphylococcus and Streptococcus (the coccus ending tells you the bacteria are round in shape). But the majority of the more dangerous bacteria test negative because of the way in which the cell wall is formed. These include the food-borne threats of Escherichia coli and Salmonella, the sexually transmitted diseases, and the bacteria most often associated with inflammation of the respiratory tract and lungs such as Legionella pneumophila.

Although science is making progress in identifying all the different types, the ones that have received the most attention are those which threaten human health. To use the technical term, they are pathogenic or cause infections by releasing toxins in your body. The most common diseases are tuberculosis and pneumonia, and they kill several million people every year. The next most dangerous group of bacteria cause food poisoning. This is ironic because a greater number of bacteria are actually positively exploited to make food taste more interesting, e.g. many cheeses are deliberately “infected”.


But, as with many topics scientific, nothing is ever absolutely true. Although some bacteria will always cause an infection, there are a few that are harmless for most of the time. For example, a range of bacteria live happily on your skin and inside your body. But, if the right conditions arise, they can turn pathogenic. This may happen because something goes wrong with your immune system, e.g. because of malnutrition or you contract AIDS, or because of some injury, e.g. an accident or surgery breaks the skin and allows bacteria entry to a less well protected area, or because you are taking medications, e.g. to suppress your immune system for transplant purposes or chemotherapy for cancer. In such cases, the benign turns harmful and makes you sick.

A further characteristic can change the level of danger. Many are relatively harmless as individual micro-organisms but, if they join or clump together, they become a greater threat. The reason for the change is that, as individuals, they are easier to kill. But when they group together, they can form a film or sheath which protects the individual cells. In this grouped form, the individual cells can act co-operatively and produce complex structures. Some change their function to produce different chemicals as required by the now multicellular organism. In effect, collectively they become small animals. When these films or groupings form around implanted medical devices, they can be almost impossible to dislodge.