There are several types of bacteria. The majority of bacteria are made up of these types:
- Gram Positive Cocci-Include Streptococcus and Staphylococcus. Bacteria that fall into this group can cause harm to the human body but can perform useful functions as well.
- Gram Negative Cocci-Include Corynebacterium diptheriae which causes diphtheria.
- Gram Positive bacilli-Includes the bacteria Neisseria meningitidis which causes a form of meningitis.
- Gram Negative bacilli-Include bacteria such as E.coli, salmonella, and shigella.
Cocci have a spherical shape while bacilli have a rod shape.
There are 3 more types of bacteria which are less common. They are:
- Spirochaetes-This type is corkscrew shaped.
- Rickettsia-Only survives inside other cells. Causes typhus.
- Mycoplasma-Has no cell wall and can cause pneumonia.
Bacteria are divided into three groups depending on their shape or morphology. Spherical bacteria are called cocci. Rod shaped bacteria are called bacilli and spiral bacteria are called spirochetes.
Cocci in clusters are called staphylococci, these cause "staph" infections. Cocci in chains are called streptococci. One type of these causes "strep throat". Bacteria in pairs are called diplococci, one type of which causes gonorrhea.
Some bacteria need oxygen to live. These are referred to as aerobic or aerobes. Other bacteria can live without oxygen, called anaerobic. Still others can live with or without oxygen and are called facultative.
There are various groups of bacteria, which belong to same family and are evolved from same bacteria (ancestor). However, each types of bacteria posses its own characteristics (those which are evolved after separation from the original specie).
Classification of Bacteria:
Bacteria are mainly classified into phylums (phylum is a scientific classification of organisms). For simplification, bacteria can be grouped into the following groups:
Bacteria classification based on shapes:
As already mentioned, before the advent of DNA sequencing, bacteria were classified based on their shapes and biochemical properties. Most of the bacteria belong to three main shapes: rod (rod shaped bacteria are called bacilli), sphere (sphere shaped bacteria are called cocci) and spiral (spiral shaped bacteria are called spirilla). Some bacteria belong to different shapes, which are more complex than the above mentioned shapes.
Aerobic and anaerobic bacteria:
Bacteria are also classified based on the requirement of oxygen for their survival. Bacteria those need oxygen for their survival are called Aerobic bacteria and bacteria those do not require oxygen for survival. Anaerobic bacteria cannot bear oxygen and may die if kept in oxygenated environment (anaerobic bacteria are found in places like under the surface of earth, deep ocean, and bacteria which live in some medium).
Gram Positive and Gram Negative bacteria:
Bacteria are grouped as ‘Gram Positive’ bacteria and ‘Gram Negative’ bacteria, which is based on the results of Gram Staining Method (in which, an agent is used to bind to the cell wall of the bacteria) on bacteria.
Autotrophic and heterotrophic bacteria:
This is one of the most important classification types as it takes into account the most important aspect of bacteria growth and reproduction. Autotrophic bacteria (also known as autotrophs) obtain the carbon it requires from carbon-dioxide. Some autotrophs directly use sun-light in order to produce sugar from carbon-dioxide whereas other depend on various chemical reactions. Heterotrophic bacteria obtain carob and/or sugar from the environment they are in (for example, the living cells or organism they are in).