State a mechanism of antibiotics in killing bacteria
Answers
The basis for selective toxicity of an antibiotic rests on the ability of the drug to attack or interfere with a structure found in bacterial cells that our cells do not have. There are 5 mechanisms by which an antibiotic can attack a bacterial cell:
Inhibition of cell wall synthesis
Inhibition of cell membrane function
Inhibition of protein synthesis
Inhibition of nucleic acid synthesis
Inhibition of bacterial enzymes / metabolic pathwayspathways
Antibiotics Active at the Cell Wall
Penicillin and its derivatives (ampicillin, amoxicillin) interfere with the ability of bacteria to build peptidoglycan. This weakens the cell wall, making gram positive cells susceptible to lysis in hypotonic environments. It tends to work best on growing cells that are building new cell wall components. Since our cells do not contain peptidoglycan, penicillin is relatively non toxic to our cells. Allergic reactions are always a possibility but not everyone experiences such complications.
Cephalosporins are considered the next generation of penicillin derivatives. This group has good activity against gram positive and gram negative bacteria. The newest ones are used against MRSA (methicillin resistant Staph aureus) infections, a particularly nasty illness. This is a good option for anyone allergic to penicillin.
Other drugs in this category include Bacitracin, a particularly effective antibiotic that is toxic to the kidneys. It is used topically for cuts and skin abrasions and is a main component of Neosporin antibiotic cream. Isoniazid is used to treat tuberculosis. Vancomycin is another commonly used antibiotic in this category which is often used for those allergic to Penicillin.
Antibiotics Active at the Cell Membrane
The main drug active on the cell membrane are the Polymyxins. They have a mode of action similar to a detergent which integrates within and disrupts the outer membrane of gram negative bacteria. The cells become sensitive to osmotic pressure as the membranes lose integrity. The cell can no longer control what goes in or out. This category of antibiotics is unique in that it is bacteriocidal, it can kill bacteria even if they are not actively growing. Due to toxicity in the kidney, this antibiotic is only used as a last resort for drug resistant strains or serious infections like a bad urinary tract infection.
The following are the mechanisms used by the antibiotics in killing the bacteria:
Explanation:
1. Prevention of the formation of cell wall of bacteria: The antibiotic named penicillin causes the break down of the bacterial cell wall and prevents its re-synthesis in bacteria. This reduces the number of bacteria in the host body.
2. Destroying the DNA replication machinery of bacteria: The antibiotic named ciprofloxacin removes the gyrase enzyme that causes the unwinding of the DNA for replication. The gyrase is inhibited by the antibiotic thus prevents the bacteria from multiplying.
3. Restriction of the protein machinery of bacteria: The antibiotic named rifamycin is the antibiotic which inhibits the synthesis of RNA in host body which will inhibit the production of bacterial protein in host body.
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