Compilation of Microbiology Staining Q&a
Introduction
Identification and classification of bacteria is important to make easier manipulation on the bacteria for various purposes such as for medical, research, developmental, and biotechnicalfieldsThe cell wall is the basis for classification of bacteria according to the Gram stain. Accordingto the chemical make up of bacterial cell wall, a staining procedure, Gram stain, helps usclassify bacteria into two subgroups, The cell wall can stain either positive or negative,depending on its chemistry. If the bacteria stains positive it will retain a purple/blue color. If the bacteria stains negative, the bacteria will not retain the purple/blue color, but rather have a pinkish/red color.Gram-positive bacteria have a thick layer of peptidoglycan external to the cytoplasmicmembrane. In contrast, Gram-negative bacteria have a thin layer of peptidoglycan located between the cytoplasmic membrane and a second membrane called the outer membrane. Thisregion is known as the periplasmic space. Figure 1 shows schematic representation of twotypes of bacterial cell wall structures. Other important constituents of the cell wall include thefollowing:
Peptidoglycan:
This is a polymer of alternating N -acetylmuramic acid (NAM) and N-acetylglucosamine (NAG). Long strands of this alternating polymer may be linked by L-alanine, D-glutamic acid, L-lysine, D-alanine tetrapeptides to NAM . Gram-positive cellshave a much more highly cross-linked peptidoglycan structure than Gram-negative cells.Peptidoglycan is also the "target" of antimicrobial activity. For example, penicillins interferewith the enzymes involved in biosynthesis of peptidoglycan while lysozyme physicallycleaves the NAM-NAG bond.
Lipoteichoic acids:
Lipoteichoic acids (LTA) are found only in Gram-positive bacteria.These polysaccharides extend though the entire peptidoglycan layer and appear on the cellsurface. As a consequence, these structures can serve as antigenic determinants.
Lipopolysaccharides:
Identification and classification of bacteria is important to make easier manipulation on the bacteria for various purposes such as for medical, research, developmental, and biotechnicalfieldsThe cell wall is the basis for classification of bacteria according to the Gram stain. Accordingto the chemical make up of bacterial cell wall, a staining procedure, Gram stain, helps usclassify bacteria into two subgroups, The cell wall can stain either positive or negative,depending on its chemistry. If the bacteria stains positive it will retain a purple/blue color. If the bacteria stains negative, the bacteria will not retain the purple/blue color, but rather have a pinkish/red color.Gram-positive bacteria have a thick layer of peptidoglycan external to the cytoplasmicmembrane. In contrast, Gram-negative bacteria have a thin layer of peptidoglycan located between the cytoplasmic membrane and a second membrane called the outer membrane. Thisregion is known as the periplasmic space. Figure 1 shows schematic representation of twotypes of bacterial cell wall structures. Other important constituents of the cell wall include thefollowing:
Peptidoglycan:
This is a polymer of alternating N -acetylmuramic acid (NAM) and N-acetylglucosamine (NAG). Long strands of this alternating polymer may be linked by L-alanine, D-glutamic acid, L-lysine, D-alanine tetrapeptides to NAM . Gram-positive cellshave a much more highly cross-linked peptidoglycan structure than Gram-negative cells.Peptidoglycan is also the "target" of antimicrobial activity. For example, penicillins interferewith the enzymes involved in biosynthesis of peptidoglycan while lysozyme physicallycleaves the NAM-NAG bond.
Lipoteichoic acids:
Lipoteichoic acids (LTA) are found only in Gram-positive bacteria.These polysaccharides extend though the entire peptidoglycan layer and appear on the cellsurface. As a consequence, these structures can serve as antigenic determinants.
Lipopolysaccharides: