Mechanism of Action of Antibiotics

Antibiotics exert their deleterious effects on bacterial pathogens mainly by disrupting protein and nucleic acid synthesis necessary for bacterial growth. These processes are also vital for human cells which should make these antibiotics as harmful to our body as they are to the invading bacteria. However, it is generally known that the administration of antibiotics effectively controls diseases by killing the offending bacteria with minimal risk of damaging human cells. This is mainly due to the difference in cell types between the human cell and bacteria. Human cells are classified as eukaryotes which are structurally and biochemically more complex than bacterial cells while bacteria are classified as prokaryotes which are primitive type of cells that are smaller and simpler. This makes antibiotics like aminoglycosides, for example, such as streptomycin to be safely effective against bacteria but not against human cells since this type of antibiotics attack the 30S subunit of the 70S bacterial ribosome causing interference with protein synthesis (Davis, 1987, p.343).

Ribosomes from human cells are not affected by aminoglycosides since they have 80S ribosomes composed of 60S and 40S subunits which are structurally different the bacterial ribosomes. Other antibiotics like sulfanilamide and trimethoprim block the conversion of para-aminobenzoic acid (PABA) into folic acid which is important for both bacteria and human cells nucleic acid and protein synthesis. Human cells are not harmed by these drugs because, unlike bacteria, human cells do not synthesize folic acid from PABA but relies mainly on folic acids from human diet as a vitamin. Beta-lactam antibiotics such as penicillin inhibits enzymes required for the synthesis of bacterial cell wall which makes them very effective antibacterial agents since human cells does not have cell walls (Tipper, 1986, p.17). There are several other differences between bacteria and human cells. These differences allow other antibiotics with different mechanisms of action to be effective in controlling bacterial growth without damaging human cells.


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