Pharmacy Exam Points (to remember)... Set 13

1. The β-lactam ring and thiazolidine ring in the skeletal structure of penicillins are collectively referred to as 6-aminopenicillanic acid. 

2. The penicillins interfere with the last step of bacterial cell wall synthesis i.e. transpeptidation or cross-linkages between peptidoglycan chains.

3. The last step of bacterial cell wall synthesis is catalyzed by transpeptidase enzyme that facilitates cross-linking of the cell wall.

4. The antibiotic penicillin irreversibly binds to and inhibits the activity of the transpeptidase enzyme. For this reason transpeptidase enzyme is also known as penicillin-binding protein, PBP. The substrate for transpeptidase resemble in structure to that of penicillins, thus transpeptidase binds to penicillins and their normal course of action is altered.

5. As a result of inhibition of bacterial cell wall synthesis, the bacterium is in a weak position which ultimately leads to its death. For this reason, cell wall synthesis inhibitors are bactericidal. 





6. Penicillins along with transpeptidase inactivate numerous proteins on the bacterial cell membrane. These penicillin-binding proteins (PBPs) are bacterial enzymes involved in the synthesis of the cell wall and in the maintenance of the morphologic features of the bacterium.

7. The number of PBPs varies with the type of bacteria. Alterations in some of these PBPs provide the organism with resistance to the penicillins.

8. Methicillin-resistant Staphylococcus aureus (MRSA) arose because of alterations in penicillin-binding proteins.

9. Many bacteria, particularly the gram-positive cocci, produce degradative enzymes (autolysins) that participate in the normal remodeling of the bacterial cell wall. In the presence of penicillin, the degradative action of the autolysins continues in the absence of cell wall synthesis. Thus, the antibacterial effect of penicillin is the result of both inhibition of cell wall synthesis and destruction of the existing cell wall by autolysins.

10. Gram-negative microorganisms have an outer lipopolysaccharide layer surrounding the cell wall that presents a barrier to the water-soluble penicillins. However, gram-negative bacteria have proteins inserted in the lipopolysaccharide layer that act as water-filled channels (called porins) to permit transmembrane entry.