Microbiology articles:
Informative articles written by scientists and medical professionals describing various aspects of microbiology. Useful for students, teachers, scientists, clinicians, and everyone with an interest in microbiology.
The Gram Stain
In microbiology, bacteria are classified as either "Gram-positive" or "Gram-negative" depending on their appearance at the microscopic level following a particular staining procedure called the Gram stain. Originally developed by Hans Christian Gram, the Gram stain is always written with an upper case "G" as it refers to the name of a person.
Gram-positive bacteria appear dark blue or violet due to the crystal violet stain following the Gram stain procedure; Gram-negative bacteria, which cannot retain the crystal violet stain, appear red or pink due to the counterstain (usually safranin).
The reason bacteria are either Gram-positive or Gram-negative is due to the structure of their cell envelope. (The cell envelope is defined as the cell membrane and cell wall plus an outer membrane, if one is present.) Gram-positive bacteria, for example, retain the crystal violet due to the amount of peptidoglycan in the cell wall. It can be said therefore that the Gram-stain procedure separates bacteria into two broad categories based on structural differences in the cell envelope.
Further reading: Microbiology
Gram-positive bacteria appear dark blue or violet due to the crystal violet stain following the Gram stain procedure; Gram-negative bacteria, which cannot retain the crystal violet stain, appear red or pink due to the counterstain (usually safranin).
The reason bacteria are either Gram-positive or Gram-negative is due to the structure of their cell envelope. (The cell envelope is defined as the cell membrane and cell wall plus an outer membrane, if one is present.) Gram-positive bacteria, for example, retain the crystal violet due to the amount of peptidoglycan in the cell wall. It can be said therefore that the Gram-stain procedure separates bacteria into two broad categories based on structural differences in the cell envelope.
Further reading: Microbiology
Labels: Gram stain, Gram-negative bacteria, Gram-positive bacteria
Peptidoglycan
The peptidoglycan sacculus is the stress-bearing structure of bacterial cells. It consists of glycan strands cross-linked by peptide bridges. Peptidoglycan, or murein as it is also known, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine and N-acetylmuramic acid residues. Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the three-dimensional mesh-like layer.
The peptidoglycan layer is much thicker in Gram-positive bacteria than in Gram-negative bacteria.
Peptidoglycan biosynthesis is the target for many antibiotics such as β-lactams, D-cycloserine and glycopeptide-antibiotics such as vancomycin. Bacteria have developed a number of different antibiotic resistance mechanisms for coping with these antibiotics.
Further reading:
Bacterial Polysaccharides
Biopolymers and Polymer Precursors
The peptidoglycan layer is much thicker in Gram-positive bacteria than in Gram-negative bacteria.
Peptidoglycan biosynthesis is the target for many antibiotics such as β-lactams, D-cycloserine and glycopeptide-antibiotics such as vancomycin. Bacteria have developed a number of different antibiotic resistance mechanisms for coping with these antibiotics.
Further reading:
Bacterial Polysaccharides
Biopolymers and Polymer Precursors
Labels: biopolymers, Gram-positive bacteria, peptidoglycan, polysaccharides
