Microbiology

Antibiotics Those Inhibit Nucleic Acid And Protein Synthesis

Synthesis of nucleic acid and protein involves a series of complex biochemical reactions. The mode of action of such antibiotics is interferes with these metabolic pathways.

Streptomycin

Streptomycin is produced by Streptomyces griseus, a soil organism. It’s antibiotic activity was reported in 1944. It is perticularly important because it inhabits many organisms resistant to sulfonamides and penicillin. It’s antimicrobial spectrum includes many Gram-negative bacteria, including Francisella tularensis and some organisms in the salmonella group. It is inhibitory for several species of Mycobacterium, including Mycobacterium tuberculosis. Highly purified streptomycin is non toxic to humans and other animals when given in small doses. But it appears to have cumulative detrimental effect on a specific region of the nervous system when given as a medication over long period of time.

Chemically, streptomycin is characterized as an aminoglycoside antibiotic. Streptomycin and other aminoglycoside antibiotics inhabit protein synthesis by combining irreversibly with 30S subunit of mRNA.

Tetracyclines

Chlortetracycline, oxytetracycline, tetracycline, doxycycline, and minocycline are generic name of five antibiotics having similar biological and chemical properties. As a group they are commonly known as tetracyclines. 

They are broad spectrum antibiotics with similar antimicrobial aspect, and cross resistance of bacteria to them in common.

Bases and hydrochloride of tetracycline are extremely stable as dry power. In solutions, tetracycline retain its activity for 3 weeks or more. Chlortetracycline and oxytetracycline are less stable. Organisms that are resistant to one are likewise resistant to other. Tetracycline have a low order of toxicity in laboratory animals. It is readily absorbed from the intestinal tract, hence it is effective when given orally.

Tetracycline inhibit protein synthesis by interference with the binding of aminoacyl-tRNA to the 30S subunit ribosome.

Chloramphenicol

Chloramphenicol is a broad spectrum antibiotic active against many Gram-positive and Gram-negative bacteria. It is bacteriostatic similar to tetracyclines.

Chemically it is a nitrobenzene ring with nonionic chlorine. The possibility of serious side effects such as blood dyscrasias have limited the use of this antibiotic as a general antibacterial agent.

By combining with 50 S ribosome, chloramphenicol inhabit protein synthesis.

Erythromycin

Erythromycin is produced by a strain of Streptomyces erythraeus isolated from soil. Erythromycin is active against Gram-positive bacteria, some Gram-negative bacteria and pathogenic spirochetes. It’s antimicrobial spectrum and clinical usefulness, is similar to penicillin, but it is also effective against organisms become resistant to penicillin and streptomycin. Patients having allergy from penicillin, can be treated by erythromycin.

Erythromycin inhibit protein synthesis by binding to 50S subunit ribosome.

Reference: Microbiology Pelczar

Nihal Sharma

Assistant Editor

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