Penicillin as an antibiotic

Today we will have discussion on Antibiotics, not the entire chapter, but, I am going to outline some points that you may find interest. This particular antibiotic has great significance and is under frequent use and one of the very first invented antibiotics. Name is ‘Penicillin’ ,which was first used in 1941 in clinical pharmacology, the first ever natural antibiotic invented by Alexandar Fleming in 1928, for which he won Novel prize. 

Chemical Nature: The nucleus of Penicillin consists of fused thiazolidine and beta lactum rings to which side chains are attached through an amide linkage.

The fusion of these two rings causes beta lactum ring to be more reactive than monocyclic beta lactum ring because the whole arrangement disturbs beta lactum amide bond and remove resonance stabilization. If we further look into it, then, side chain of Penicillin can be split off by an amidase to produce 6-aminopenicillanic acid, turns out; other side chains can then be attached to it resulting in different semisynthetic Penicillins with unique anti-bacterial activities with different pharmacokinetic profiles.

Mechanism of Action:   In simple way, when susceptible bacteria divide in the presence of a beta lactum antibiotic, cell wall deficient forms are produced. Because the interior of the bacterium is hyperosomatic, the CWD forms swell and burst leading to bacterial lysis. If you go further in it, then, as a beta lactum antibiotic it interferes with the synthesis of bacterial cell wall. The bacteria synthesize UDP-N-acetylmuramic acid pentapeptide(park nucleotide) and UDP-N-acetyl glucosamine. The peptidoglycan residues are linked together forming long strands and UDP is split off. The final step is cleavage of the terminal D-alanine of the peptide chains by transpeptidases. The released energy is utilized for establishment of cross linkages between peptide chains of the neighboring strands. This cross linking provides stability and rigidity to the cell wall. Besides, beta lactum antibiotics inhibit the transpeptidases so that cross linking does not take place. These enzymes and related proteins constitute the penicillin binding proteins, located in the bacterial cell membrane.

*** Lytic effect of these antibiotics may also be due to depression of some bacterial autolysins which normally function during cell division

I will discuss about semisynthetic products of penicilin and its advantages.