What are the differences between gram-positive and gramnegative bacteria?
Gram-positive and gram-negative bacteria are two major groups of bacteria
that have different structures, behaviors, and responses to antibiotics. These
differences are mainly based on the differences in the structure of their cell
walls and outer membranes.
Gram-positive bacteria have a single, thick layer of peptidoglycan that forms a
rigid structure around the cell. This layer is surrounded by a layer of
lipoteichoic acid and a thick layer of polysaccharides or teichoic acids, which
provide additional support to the cell wall. Gram-positive bacteria do not have
an outer membrane, and their cell walls are permeable to most substances.
In contrast, gram-negative bacteria have a thinner peptidoglycan layer
surrounded by an outer membrane made up of lipid bilayers and
lipopolysaccharides. This outer membrane also contains porins that allow the
entry of molecules into the periplasmic space. The periplasm contains a
variety of enzymes and transporters that help the cell uptake and process
nutrients. The outer membrane of gram-negative bacteria is not very
permeable and can block the passage of many antibiotics.
Gram-positive and gram-negative bacteria also differ in their response to
antibiotics. Gram-positive bacteria are generally more susceptible to
antibiotics that target the cell wall, such as penicillin and vancomycin. In
contrast, many gram-negative bacteria are resistant to these antibiotics due to
the presence of an outer membrane.
In summary, the main differences between gram-positive and gram-negative
bacteria are the structure of their cell walls and outer membranes, the
presence of lipoteichoic or lipopolysaccharides, and their responses to
antibiotics.
References:
1. Proctor, R. A., & Peters, G. (2015). Small colony variants in staphylococcal infections:
diagnostic and therapeutic implications. Clinical infectious diseases: an official publication of
the Infectious Diseases Society of America, 61(3), 401-406.
2. Nikaido, H. (1996). Outer membrane. Escherichia coli and Salmonella: cellular and
molecular biology, 1, 29-47.
3. Penicillin and Other β-Lactam Antibiotics. (2016). In Antimicrobial Pharmacodynamics in
Theory and Clinical Practice (pp. 259-281). CRC Press.