Classification System of Bacteria

Based on differences in the cell wall structure the kingdom prokaryote is divided into four of divisions:-

·         Gram positive cell walls.

·         Gram negative cell walls.

·         Cells without walls.

·         Cells with unusual walls.

The bacterial sub-types are next classified into genera related to genus and species.

Members of a genus share the same heredity; however they different from each other in the certain morphological and behavioral ways; for example the early human and modern human belong to the same genus; other level of species; classification of bacteria and humans differs; in humans and other animals the terms species refers to a natural population that cannot successfully breed with another group like (Neanderthal) and modern humans; in contrast bacteria within a species are similar to another as one human is similar to another human; finally some bacterial species may be divided further into strains that share a particular characteristic but it is not common to the rest of the species; individuals of the same strain are equivalent to identical twins since their old descendants of the same parental cell; in clinical medicine the shared characteristic that define the particulars strain is often resistance to an antibiotic to which the species was one susceptible; the relationship of individual bacteria to another is often described by a system of binomial nomenclature in which the name for a species of bacteria consists of two parts both of them usually in Latin or Greek; in the bacterial species named “Streptococcus pneumoniae”; thus “Streptococcus” is the genus and “pneumoniae” represents the species; in stand of usage; the genus is always capitalized while the species is not; additionally the genus name is written note as first time it appear in a document that is an abbreviated as a single initial thereafter “Streptococcus pneumoniae” becomes “S. pneumoniae”.

The major characteristics used to classify bacteria into genus and species are:-

·         Cell shape and arrangement.

·         Gram stain reaction.

·         Oxygen requirements.

·         Nutritional and metabolic characteristics.

Differences in cell shape and arrangement provide an initial clue to the identity of the bacterial genus and species.

The three basic shapes of bacterial cells are:-

• Coccus (round).
• Bacillus (rod shaped).
• Spirochetes (spiral).

Some coccoid bacteria or cocci exist as single cells; however the when other cocci divide and reproduce; individual bacteria remain attached to the each other; these group include pairs of  a cells (Diplococci); chains of cells (Streptococci) and clusters of cells (Staphylococci);

A major characteristics for classifying bacteria is the gram stain reaction which distinguishes two types of bacterial cell walls; grams stain dye process stain gram positive bacteria dark violet and gram negative bacteria red.

Due to several layers of peptidoglycans network which is made up of amino acids and simple sugar molecules linked by chemical bridges; the cell walls of gram positive bacteria are more rigid and stronger than those gram negative bacteria; in contrast gram negative cell walls are more vulnerable to breakage than the thicker, strong walls of gram positive cells.

However a gram negative cells are quite complex; between the cell wall and outer membrane and the cytoplasmic membrane of gram negative cells is an enzyme filled gel compartment called periplasm; impeded in the gel a small peptidoglycans backbone to provide some strength to the wall; more importantly gram negative cell walls contain Lipopolysaccharides molecules made of sugars and fats that is not found in most gram positive cell walls; these molecules are involved in the formation of toxins that can be harmful to the human upon their release.

Bacteria differ in their need for and tolerance of oxygen on the basis of whether they can use oxygen for their growth and metabolic processes; bacteria are classified generally as:-

·         Aerobic or aerobes which use oxygen.

·         Anaerobic or anaerobes which do not use oxygen.

Aerobic bacteria are fragile since they require oxygen for life and the loss of oxygen in their environment kill them; some aerobes are classified as Microaerophilic because they require oxygen in a concentration lower than that present in the atmosphere; in contrast many anaerobes are less fragile in particular Facultative anaerobes which use oxygen when it is available; and can survive without it (most adaptive bacteria).

Anaerobes also include Aerotolerant and Obligate bacteria; aerotolerant anaerobes cannot use oxygen but they usually not damaged by oxygen; obligates anaerobes are unable to use oxygen and are damaged by oxygen.

Carbohydrate metabolism is another distinguishing factor used in classifying bacteria; for example among number of similar bacteria that inhabit the human intestinal tract; only certain species metabolize carbohydrates such as lactose - a milk derived sugar -; therefore the presence of intestinal gas a byproduct of lactose metabolism indicates the presence of these specific bacteria.