Antibiotics Those Inhibit Cell Wall Synthesis

Among the antibiotics whose antimicrobial action is by inhibition of biosynthesis of peptidoglycan cell-wall structure are the penicillins, cephalosporins, cycloserine, vancomycin, bacitracin.

Peptidoglycan is the substance which give rigidity to the cell wall. It is a protective covering for many bacterial cell.

Biosynthesis of peptidoglycan involves numerous steps. Interference in any of the step may inhibit cell wall synthesis. And result in the inability of the bacterium to survive because of the absence of the protective covering ( cell wall ).

The Penicillins

The first of the modern antibiotics, and still one of the most useful, penicillins, is produced by Penicillium notatumPenicillium chrysogenum, and by other species of molds. As we know the first of these was isolated by Fleming in 1929, when he found it as a contamination on the culture plate.

Penicillin is selective for Gram positive bacteria, some spirochetes, and the Gram negative diplococci. Although it is rarely toxic in human patients, it may give rise to sensitivity reactions which vary from a mild skin reactions to severe anaphylaxis.

On the basis of source, penicillin may be of two type “natural penicillin” the one which is produced by biosynthesis. And “semisynthetic penicillin” which is produced or developed in laboratory.

One of the first semisynthetic penicillin to be produced for clinical use was phenethicillin. It is more readily absorbed than penicillin V and just as effective as penicillin G. Another of the semisynthetic penicillins, methicillin is more resistant to penicillinase and therefore is less likely to be inactivated.

Ampicillin

Ampicillin, another semisynthetic penicillin, acts against a broad spectrum of bacteria. It is strongely bactericidal and lack Toxixity but it is not registrant against penicillinase. It can be administered orally, because it is relatively stable to gastric acid. Several additional semisynthetic penicillins have been developed for chemotherapeutic use.

Penicillins interferes with the final stage of peptidoglycan biosynthesis.  The penicillins are bactericidal to growing cells.

Cephalosporins

Cephalosporins is a group of antibiotics those are developed by a marine fungus Cephalosporium acremonium, which bears considerable resemblance to Penicillium spp.

They are effective against Gram positive bacteria and Gram negative bacteria.

Cephalosporins and semisynthetic Penicillin have similar antibacterial properties. They are effective therapeutically and have a low toxicity. As with penicillins several semisynthetic cephalosporins have been manufactured commercially for therapeutic use.

Mode of action of cephalosporins is that of inhibition of the cross-linking transpeptidase. They are bactericidal to growing cells.

Cycloserine

Cycloserine is relatively simple compounds, it’s structure is similar to Alanine. It was originally discovered by streptomyces and is know manufactured through chemical synthesis.

It’s maimly used in tuberculosis therapy. However, because of its potential undesirable side effects, it’s utilisation is limited.

Cycloserine manifest its inhibitory effect on peptidoglycan synthesis by interference with synthesis of the peptide moiety of the peptidoglycan. 

Bacitracin

Bacitracin is a product of Bacillus subtilis and chemically is a polypeptide. Because of its toxic effect on human cells, it cannot be used as chemotherapeutic agent. It does have application for tropical treatment of infections caused by Gram-positive bacteria.

Bacitracin interferes with regeneration of the monophosphate form of bactoprenol from the pyrophosphate form.

Vancomycin

Vancomycin is an antibiotic produced by Streptomyces orientalis. It is a complex chemical entity consisting of amino acids and sugars.

Vancomycin inhibits peptidoglycan synthesis by binding the D – alanyl – D – Alanine group on the peptide side chain on one of the membrane bound intermediates.

Reference: Microbiology Pelczar

Gaurav Singh

Editor in Chief Medical Microbiology & RDT Labs - RDT Labs Magazine | BSc Medical Microbiology | MSc Microbiology

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