Gram positive bacteria: are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain (safranin or fuchsine) and appearing red or pink. Gram-positive organisms are able to retain the crystal violet stain because of the high amount of peptidoglycan in the cell wall. Gram-positive cell walls typically lack the outer membrane found in Gram negative bacteria.
- gram positive bacteria
Characteristics
- cytoplasmic lipid membrane
- thick peptidoglycan layer
- teichoic acids and lipoids are present, forming lipoteichoic acids, which serve to act as chelating agents, and also for certain types of adherence.
- capsule polysaccharides (only in some species)
- flagellum (only in some species)
- if present, it contains two rings for support as opposed to four in Gram-negative bacteria because Gram-positive bacteria have only one membrane layer.
- The individual peptidoglycan molecules are cross-linked by pentaglycine chains by a DD-transpeptidase enzyme. In gram-negative bacteria, the transpeptidase creates a covalent bond directly between peptidoglycan molecules, with no intervening bridge.
Both Gram-positive and Gram-negative bacteria may have a membrane called an S-layer. In Gram-negative bacteria, the S-layer is attached directly to the outer membrane. In Gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Unique to Gram-positive bacteria is the presence of teichoic acids in the cell wall. Some particular teichoic acids, lipoteichoic acids, have a lipid component and can assist in anchoring peptidoglycan, as the lipid component is embedded in the membrane.
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