CELL MEMBRANE

Cell Membrane

There are types of antibiotics that disrupt the structure of the cell membrane. The cell membrane is integral to the health and structure of the bacteria. It acts as a permeability barrier allowing the cell to control which substances are kept inside and outside of the cell.

Gram positive bacteria have a plasma membrane and a thick peptidoglycan layer, whereas Gram negative bacteria have a plasma membrane, a thin peptidoglycan layer, and an outer membrane (see Figure 1).

There are different kinds of antibiotics that target the cell membrane. Daptomycin targets the plasma membrane of gram positive bacteria, while polymixin targets the outer membrane and then plasma membrane of gram negative bacteria.

Gram Positive_ Negative structure (2).pn

Figure 1. Gram positive and gram negative cell wall structures.

Daptomycin antibiotics

Daptomycin forms a complex with calcium, and is inserted into the plasma membrane of Gram positive bacteria. These complexes aggregate to form pore-like structures in the membrane which allow ions such as potassium to leak through from the cytoplasm to the external environment. This results in the depolarisation of membrane potential and death of the bacterial cell (Pogliano et al. 2012).

Figure 2. Daptomycin mechanism of action on Gram positive plasma membrane.

Polymixin antibiotics

Polymixin binds to the lipopolysaccharides on the outer membrane of Gram negative bacteria. This causes structural changes of the outer membrane, which increases membrane permeability, and allows polymixin to disrupt the structure of the plasma membrane. This leads to leakage of the cell contents and death of the bacterial cell (Velkov et al. 2013).

Figure 3. Polymixin mechanism of action on Gram negative outer and plasma membrane.

References

Pogliano J, Pogliano N, Silverman JA (2012) Daptomycin-mediated reorganization of membrane architecture causes mislocalization of essential cell division proteins. Journal of Bacteriology. 194 (17): 4494–504.

Velkov T, Roberts KD, Nation RL, Thompson PE, Li J (2013). Pharmacology of polymyxins: new insights into an 'old' class of antibiotics. Future Microbiology. 8 (6): 711–724.