Bacteria are mainly divided into two main groups, gram-positive and gram-negative, depending on their Gram stain retention property.The phrase ‘gram-positive’ is usually a term used by microbiologist to classify bacteria into two groups (gram-positive or gram-negative). This positive/negative reference is dependent on the bacterium’s chemical and physical properties of the cell wall.
To determine whether a bacteria is gram-positive or gram-negative a microbiologist will perform a special type of staining technique, called a Gram Stain. The name comes from its inventor, Han Christian Gram (1884). This stain will either stain the cells in purple (for positive) or pink (for negative) color.
Gram-positive bacteria retain the color of the crystal violet stain while in the Gram stain. This is certainly characteristic of bacteria which have a cell wall made up of a thick layer of the particular substance called peptidoglycan.
Usually, gram-positive bacteria are the helpful, probiotic bacteria. They are the satisfied ones that live in our gut and help us digests food.But Gram-positive bacteria will also be pathogenic. Clostridium botulinum, the bacterium responsible for producing neurotoxins which could kill in hours is a gram-positive bacterium. The Gram-positive bacteria include staphylococci ("staph"), streptococci ("strep"), pneumococci, and the bacterium responsible for diphtheria(Cornynebacterium diphtheriae) and anthrax (Bacillus anthracis). The archetypal hospital "superbug", methicillin-resistant S. aureus (MRSA), regularly attracts mass-media interest.
In general, the characteristics are present in gram-positive bacteria are include:
· Cytoplasmic membrane made up of lipid.
· Thick peptidoglycan cell wall.
· Teichoic acids and lipoids exist, forming lipoteichoic acids, which function as chelating agents, and also for several kinds of adherence.
· Peptidoglycan chains are cross-linked to make rigid cell walls by the bacterial enzyme DD-transpeptidase.
· A smaller volume of periplasm than that in gram-negative bacteria.
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