Antibiotics are commonly used to treat microorganisms or bacteria, but they do not function against viruses or fungi. They are only effective against bacteria. Sir Alexander Fleming discovered the first antibiotic in 1928, a discovery that has been referred to as one of the most significant victories over disease!
But how do antibiotics work? There are multiple types of antibiotics, and they work in different ways. Some antibiotics disrupt the cell membrane integrity, while others interfere with essential metabolic pathways or inhibit nucleic acid synthesis. They all have one thing in common, however: they target essential processes in the cell and prevent bacteria from spreading either by killing them directly or inhibiting their growth.
To understand more about this, we need to dig into the antibiotic classifications. Here are a few examples:
• Inhibition of cell wall synthesis mechanism of action: One class of antibiotics targets the cell wall synthesis process. The bacterium has a cell wall membrane and a cell wall made of peptidoglycan, which are sugar molecules linked together by peptide bonds. Without the essential peptide, the cell wall becomes unstable, and the cell may even burst due to the high osmotic pressure inside. Penicillin is a beta-lactam antibiotic that inhibits the activity of transpeptidase, which is necessary for cell wall construction. Without transpeptidase activity, there is no cell wall construction, and bacteria are destroyed.
(Figure 1: inhibition of cell wall synthesis)
Note. This image explains how its synthesized by an enzyme called transpeptidase catalyses the reaction necessary to crosslink peptidoglycan, this mechanism is the target of the antibiotic penicillin that inhibits the activity of the enzyme transpeptidase. (image source: Henrik's lab)
• Inhibition of protein synthesis mechanism of action: Some antibiotics suppress protein production. Bacterial mRNA must be translated into protein, and ribosomes are the catalytic machinery of translation. Tetracyclines are antibiotics that interfere with the ribosomes, preventing protein synthesis from occurring. This does not directly kill the bacteria, but it depletes them of protein required for growth
(Figure 2: inhibition of protein synthesis)
Note. This image explains how the bacterial mRNA needs to be translated into protein, ribosomes are the responsible catalytic machinery of translation which are the two pink pieces, the bacterial ribosomes consists of two units the bigger one is 50s and the smaller one is 30s, tetracyclines is an antibiotic that interferes with the small 30s subunit so tRNA can no longer bind to the ribosomes. (Image source: Henrik's lab)
• Inhibition of nucleic acid synthesis mechanism of action: Some antibiotics target the stage before translation, hindering nucleic acid synthesis. Bacterial DNA is normally transcribed by an enzyme called RNA polymerase, which synthesizes mRNA through a process known as transcription. Rifamycin is an antibiotic that inhibits the enzymatic activity of RNA polymerase, stopping mRNA synthesis and indirectly protein formation.
(Figure 3: inhibition of nucleic acid synthesis)
Note. This image explains how the antibiotic Rifamycin inhabit the enzyme activity of RNA polymerase to stop mRNA synthesis which will indirectly stop the protein production! (Image source: Henrik’s lab)
You might still be confused, well, let me break it down for you in a simplified version: Antibiotics work by targeting essential processes in bacteria, making it hard for them to survive. Some antibiotics, like penicillin, stop the cell wall from forming, while others, like tetracyclines, prevent protein production. Another type of antibiotic, like rifamycin, blocks the creation of genetic instructions, making it hard for bacteria to grow. These antibiotics are designed to affect bacteria specifically, without harming human cells
Now this is how antibiotics are a threat:
Antibiotics are a threat due to their overuse. The use of antibiotics became widespread after World War II when soldiers returned from battle with infections that were treated with antibiotics. This led to antibiotics being referred to as "wonder drugs." Today, antibiotics are not only used to treat humans but also administered to livestock to keep them healthy and prevent disease.
Overusing antibiotics promotes antibiotic resistance. Antibiotic resistance is caused by simple mutations in bacterial DNA. These mutations occur frequently in all organisms, but when an antibiotic is used and one microbe develops resistance to this drug due to random mutation, this drug becomes ineffective. Other antibiotics may be used to treat the infection, but if these too become ineffective due to selection pressure on the microbes, it could lead to multiple drug resistance.
In the worst-case scenario, no antibiotic could be effective anymore, and we would be left with super germs that could cause the next big pandemic. Multi-resistant microbes are already among us, which is why we must be more responsible with the use of antibiotics in the future.
Science is working on developing new antibiotics to combat this problem, but our job is to be more responsible with the use of antibiotics now!
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