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Mode of Action of Antibiotics

BY: Nidhi Uppangala | Category: Biology | Submitted: 2010-09-07 07:37:04
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Article Summary: "Antibiotics are chemical molecules or compounds that specifically targets and kill cells. Antibacterial action generally follows some of the mechanisms such as inhibition or regulation of enzymes involved in the synthesis of cell wall, nucleic acid synthesis and repair, or protein biosynthesis. Antibiotics target the cell functi.."


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Introduction:

Antibiotics are chemical molecules or compounds that specifically targets and kill cells. Not only antibacterial, but also antifungal, antiviral and also antineoplastic compounds are also classified as antibiotics.

Antibacterial action generally follows some of the mechanisms such as inhibition or regulation of enzymes involved in the synthesis of cell wall, nucleic acid synthesis and repair, or protein biosynthesis. Antibiotics target the cell functioning of rapidly dividing cells.

Inhibition of Cell Wall Synthesis:

Bacterial cell contains a peptidoglycan cell wall in addition to the normal inner plasma membrane, surrounding the cellular contents. In other words bacterial cells resemble the primitive plant cell structure. In addition to these Gram-negative bacteria also has outer lipid bilayer.

Some of the antibacterial compounds interfere with the cell wall synthesis by weakening the peptidoglycan structures in bacterial cell wall, by this integrity of bacterial cell wall structure weakens and eventually disrupts. Mammalian cells only have plasma membrane so these antibiotics specifically target only bacterial cells. That is these antibiotics do not induce any negative effect on the host mammalian cells.

The specificity of antibacterial compound β-lactam is by their ability to prevent the assembly of peptidoglycan layer via inhibiting transpeptidase enzyme activity. Antibacterial compound β-lactam can be used against both Gram-positive and Gram-negative bacterial cells.

Vancomycin another antibacterial compound also prevents cell wall biosynthesis in bacterial cells by interfering with transglycosylases enzyme activity. But this compound can be used effectively against Gram-positive bacteria, as it is unable to penetrate the outer cytoplasmic membrane of Gram-positive bacteria.

Some of the antibacterial examples for this type of action are

Bacitrasin extracted from Bacillus licheniformis, D cycloserine, antibacterial compound Tunicamycine extracted from Streptomyces species, another antibacterial compound called as Vancomycin hydrochloride extracted from Streptomyces orientalis potency.

Inhibition of Nucleic Acid Synthesis:

This category of antibacterial compounds interferes in the synthesis of nucleic acid of bacterial cells. For example compound quinonoles interfere with synthesis of DNA molecule by inhibiting activity of enzyme topoisomerase. This enzyme is involved in the DNA (deoxy nucleic acid) replication.
The second generation quinolones like levofloxacin, norfloxacin and ciprofloxacin all can be used against both Gram-positive and Gram-negative bacteria. These compounds specifically inhibit the bacterial topoisomease II.

Quinoline compounds that have the capacity to inhibit mammalian cell topoisomerase are used to treat patients with cancer, for example asirinotecan and etoposide.

Some antibiotics inhibit the action of enzyme RNA polymerase, hence interfere with RNA (ribonucleic acid) synthesis in the cells. Antibiotics such as asdoxorubicin andactinomycin D interfere with RNA biosynthesis in both bacterial cells as well as in mammalian cells. These compounds are used in treating rapidly growing tumor cells in cancer patients.
Some of the examples are Doxorubicin hydrochloride, Levofloxacin, Irinotecan hydrochloride, Rifampcin.

Inhibition of Protein Synthesis:

Some of the antibiotic compounds inhibit bacterial cell multiplication by inhibiting protein synthesis in them. Protein synthesis is a multi-step process. Majority of antibiotics inhibit the process that occurs in the 30S 0r 50S subunit of 70S bacterial ribosome, this in turn inhibits the protein biosynthesis.

Most of the antibiotics inhibits the formation of 30S initiation complex or altogether inhibits the formation of 70S ribosome by the 30S and 50S ribosome subunits or they inhibit assembling of amino acids into a polypeptide chain.

Tetracyclines, includingdoxycycline, block protein synthesis by preventing the binding of aminoacyl-tRNA in 30S ribosome subunit. These compounds block protein synthesis in both prokaryotic and eukaryotic system.

Streptomycin interferes with the formation of 30S initiation complex hence inhibits the protein biosynthesis. Erythromycin interferes with the assembly of 50S subunit of ribosome hence inhibit the protein synthesis.

Antibiotics lincomycin and clindamycin inhibits enzyme peptidyl transferase, hence prevent the protein synthesis.

Whereas antibiotic puramycin does not inhibits the enzymatic process, but they act as an analoge of 3'-terminal end of aminoacyl-tRNA, hence disrupts protein synthesis and causes premature polypeptide chain termination. In other words this antibiotic produces non functional proteins in the cell.

Some of the examples for this category of antibiotics are Doxocycline hyclate, Erythromycin, Hygromycin B, Kanamycin disulfate salt and much more.

Conclusion:

Antibiotics inhibits the growth of infectious agents such as bacteria, virus, fungus or other types of microorganisms by inhibiting cell wall formation or nucleic acid synthesis or protein synthesis.

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Comments on this article: (1 comments so far)

Comment By Comment
buvani S
2011-05-10 22:01:04 161
The article is highly informative. In the Cell wall section, de script ion of Vancomycin contains a line "can be used against Gram+ve as it is unable to penetrate Outer memb. of Gram +ve" instead of Gram -ve. Posting this comment just to clarify.

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