1. Effect of antibiotics on membrane functions

2. Functions of the cytoplasmic membrane It forms an expandable and protective barrier to the protoplast. Provides a site for the synthesis of cell wall. Acts as organelle controlling the entry and exit of solute molecules.

3. Antibiotics affect cell membrane function through 3 different mechanisms: 1- Acting by producing disorganization of cell membrane (e.g polymxins and polyenes). 2- Inhibits protein bound to membrane and involved in transport process (oligomycin).

4. Polymyxins It is suggested that polymyxins reacts with lipophilic and lipophobic groups in the membrane and that its molecules are oriented in the interphase between lipid and protein layers of membranes of E. coli. Polymyxin also caused marked degradation of the lipid fraction of bacteria. TLC shows that degraded lipids were phosphatidyle ethanolamine and phosphatidyl glycerl, which form 80% and 15 % of total bacterial phospholipid bilayer respectively.

5. 3-Produce specific changes in permeability towards specific ions. polymyxin B also caused activation and release of alkaline phosphatase which is located at the cytoplasmic membrane.

6. Polyenes (e.g Nystatin ) Poleyene + microbial cell Membrane- polyene complex Altered membrane permeability -Leakage of K+ and sugars - impaired conc mechanism - death due to loss of NH4+, Pi acids and nucleotides -Leakage of proteins pH 5.5 Internal acidification and autolysis

7. Antibiotics as ionophores Valinomycin and gramicidin Generally microbial membranes are impermeable to K+ ions. Experiments showed that streptococcus membranes are permeable to K+ and Rb + cations in presence of valinomycin and gramicidin.

8. Growth inhibition of Streptococcus by valinomycin and gramicidin is associated with loss of K+. Ionophores antibiotics are able to form lipid soluble complexes that allow inorganic cations to traverse lipid barrier and cell membranes. “They are lipophilic”

9. The increased permeability to K+ induced by these antibiotics was the explanation for the inhibition of: - Growth - Glycolysis - Protein synthesis - other process