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Antibiotics: An overview

Antibiotics are a type of medicine which are used to treat bacterial infections.
Every day we come into contact with thousands of bacterial cells. We are colonized with lots of different types of bacteria which live on us, and inside of us; everywhere from the grooves of your fingerprint, to the nooks and crannies of your intestines. If you count up all of the bacteria, they actually outnumber us (by "us" we mean our human cells) about 10 to 1. To stay healthy, we need to maintain a healthy ecosystem of bacteria, called normal flora (not all bacteria are bad!), while selectively getting rid of the harmful, “pathogenic” bacteria which can cause an infection.
Pathogenic bacteria is a relative term. Some bacteria can cause illness in you no matter what. Other bacteria cause illness when they wander from their normal location (e.g. intestines) and try to live in a new location (e.g. bladder), which is what happens when you develop a urinary tract infection (UTI). The body’s immune system responds to an infection by trying to fight and destroy the invading bacteria!

What are antibiotics?

To help the immune system, we sometimes use antibiotics, which are chemicals (specifically a swarm of small molecules) that enter and stick to important parts (think of targets) of the bacterial cell, and interfere with its ability to survive and multiply. If the bacteria are susceptible to the antibiotic, then they will stop growing or simply die.
These important parts include:
  • Proteins/sugars in the bacterial wall
  • Important enzymes that make new bacterial DNA or proteins
When an antibiotic molecule sticks to its target, it will disable or destroy that protein or enzyme. If enough of the antibiotic is present, the bacterial cell is crippled and either stops growing (bacterio-static effect) or simply dies (bacteri-cidal effect).
Just to be clear, antibiotics don’t affect viruses, fungi, or parasites - they only bind to bacterial cell targets so they only affect bacterial cells. In fact, they specifically target bacteria rather than human cells.

How were antibiotics discovered?

Back in 1928 (right before the great depression), Alexander Fleming first discovered the antibiotic Penicillin when he noticed that bacteria in his lab wouldn’t grow near some fungus, which had accidentally found its way into his experiments. The fungus was making a small molecule which leaked into the petri gel around it, and Fleming called the stuff - “mold juice”. He realized that the mold juice was killing the bacteria in the area! The next big surprise for Mr. Fleming came when he later found out that the fungus was the same bluish-green fungus that grows on old bread. The discovery earned him the Nobel Prize in 1945, and helped humanity develop a key antibiotic which has saved countless lives.
In his Nobel Prize acceptance speech, Fleming warned the world of the dangers of misusing antibiotics. He had already noted bacteria in his lab becoming resistant to penicillin, just a few years after its discovery! After decades of antibiotic misuse, today we find ourselves facing bacteria which has become resistant to most, if not all antibiotics.

How do antibiotics work?

Let's take a look at a couple of examples of antibiotics: Penicillin and Azithromycin.
Penicillin is a fabulous antibiotic because it isn't toxic to humans at concentrations that can kill bacteria and it can kill a lot of different types of bacteria.
So how does it work?  Penicillin weakens the bacterial wall by:
  • Deactivating a bacterial enzyme (transpeptidase) that builds and repairs the bacteria wall.
  • Activating a bacterial enzyme (autolysin) that cuts open parts of the bacterial wall, an enzyme normally only activated when the bacteria is multiplying.
In short, penicillin causes the bacteria to weaken its own cell wall (imagine being forced to punch yourself!), and prevents the bacteria from being able to repair itself. With a weak wall, water seeps in, and the bacteria swells up and explodes.
Azithromycin is a broad spectrum antibiotic which is often used to treat a wide variety of infections; everything from pneumonia to sexually transmitted diseases.
So how does it work?
Azithromycin prevents the bacteria from multiplying by:
  • Blocking the cell's ability to create proteins by attaching to ribosomes in the cell.
In short, azithromycin prevents bacteria from multiplying, making it much easier for the immune system to handle the infection.

Antibiotic development

Over the years, a number of antibiotics have been discovered in nature or synthesized in the lab. Some antibiotics target only specific bacteria and are called “narrow spectrum” antibiotics, whereas other antibiotics target many types of bacteria and are called “broad spectrum” antibiotics.
Developing completely new classes of antibiotics (as opposed to variations on existing antibiotics) is very difficult. It’s easy to find chemicals that kill bacteria, but not so easy to find substances that could be used as medicines, even if researchers were given infinite resources! Researchers are basically shooting in the dark. In fact, the most recent discovery of a novel antibiotic class was in 1987, more than 30 years ago (Silver, L., 2011)! While there are a few new antibiotics currently in development, researchers don’t know if they’ll ever become usable as medicine.
This void in the discovery of new antibiotics is problematic. When a bacteria becomes resistant to a specific drug within a drug class, it gains some level of resistance to drugs within the same class. For example, if a bacteria became resistant to ampicillin, it would also have some level of resistance to other penicillin-like antibiotics.

Want to join the conversation?

  • hopper cool style avatar for user Sohan
    Do antibiotics fight the bacteria or boost the immune system
    (8 votes)
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  • leaf green style avatar for user hocarts
    In the time line figure the antibiotic Salvarsan was discovered before penicillin. Who discovered this and did they get any recognition in the way of Nobel prizes like Fleming? If not, why is penicillin seen as the first big break through with regard to antibiotics?
    (5 votes)
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  • duskpin ultimate style avatar for user Kirk Dakota
    I am a college student studying towards my pre pharmacy degree. I am actually writing a paper on antimicrobial resistant bacteria and remembered reading this article on khan academy. But I would like to do a little more research into this topic specifically on how antimicrobials work on bacteria. Is there a resources section for this article that I would be able to dig a little deeper into?
    (2 votes)
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  • female robot grace style avatar for user Mira
    Under the "How were antibiotics discovered" part, in the second paragraph, you said that some bacteria become immune to antibiotics. Does this happen only when it is overused?? And when it DOES eventually become immune, does it only affect the person that's been taking too many pills, or does that entire bacteria become immune to that drug?
    (2 votes)
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    • purple pi teal style avatar for user Ben Doucette
      A bacteria becomes resistant to a drug (such as penicillin) because it has been exposed to it and it developing an immunity to it. Your body does the same thing when attacked by bacteria or viruses. If the bacteria become resistant and then reproduce, then the new bacteria will be resistant as well. This is the quote, "He had already noted bacteria in his lab becoming resistant to penicillin, just a few years after its discovery!" The part where it says "in his lab" is the key to your question. So, not all bacteria will become resistant to the drug if misused, just the bacteria that are being exposed to the drug.

      Hope that helps!
      - Ben Doucette
      (2 votes)
  • leafers seed style avatar for user Allison S.
    Under the section "What are antibiotic?", it claims that antibiotics only affect bacteria ,but not parasites ,viruses, or fungi. Then what affects the rest (parasite,virus,fungi)?
    (2 votes)
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    • aqualine ultimate style avatar for user Alex Liu
      The only part of your question that I can answer is the virus part. The antibiotics don't affect viruses simple because of what viruses do. Viruses are blobs of genetic info, designed to enter your body's cells and turn your cells in to machines that create more viruses. Their goal is to reproduce. Some harm you and destroy cells, while others just use the cell for a while then they leave. In the article it explains how the antibiotics work, so you can see how it wouldn't affect viruses.
      (2 votes)
  • leafers seed style avatar for user abdo barakat
    So,Why Antibiotics doesnot use to destroy cancer ?
    (0 votes)
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    • leaf green style avatar for user Joanne
      Why questions are difficult to answer. Anti-biotics target micro organisms that abnormally grow and use our body for their nutrition. The best antibiotic treatments target something unique in the bacteria that mammal cells do not have. Bacteria and cancer are different living cells, they are not the same type of problem. Cancer is a huge category of human cells that abnormally grow and use our body for their nutrition. We are eating ourselves, growing tumors. There is nothing (or little) unique in a cancer cell that is different from a normal cell to attack with a drug except the fact that they are dividing out of control. These are very different reasons to be ill and they require different treatments. Antibiotics kill bacteria not human cells. This 'why' question is like asking why are there so many spices, why don't we just use pepper? Not all soups benefit from more pepper, some need salt. That is why.
      (8 votes)
  • piceratops tree style avatar for user Rahul Kunte
    How Exactly does a bacteria grow resistance to any antibiotic? And how does our body make sure to not breakdown the antibiotic to simpler compounds and how does the antibiotic know where to go?(I mean which part of the body eg: Lungs etc).
    (2 votes)
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    • leaf blue style avatar for user Esther Dickey
      Some bacteria are naturally resistant to the antibiotic. All the others are killed by the antibiotic, but those few resistant ones aren't. Then those resistant ones are the only bacteria of that species in the body. If they divide and grow, then you end up having a large population of bacteria that are all resistant to that antibiotic.

      I expect that doctors use compounds which are not easily broken down.

      The antibiotics go throughout your body, targeting whatever bacteria they meet.

      Hope this helps!
      (2 votes)
  • winston baby style avatar for user 👾Riley👾
    Are some antibiotics toxic to humans?
    (2 votes)
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    • hopper cool style avatar for user Madeliv
      There are substances that kill bacteria, but which are harmful for humans (like chlorine, which we use to clean toilets, which kills nearly 100% of all bacteria but is very damaging to humans) but these are never used as antibiotics! Only medicines that kill bacteria without harming humans are selected for antibiotics.
      (2 votes)
  • duskpin ultimate style avatar for user Jaiden
    So if it takes THAT LONG for researchers to find a antibiotic could there be a new bacteria that no antibiotic could get rid of would it just wipe out the whole human race if the bacteria is bad enough?
    (2 votes)
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  • aqualine ultimate style avatar for user Elkan.Zhang
    Why don't antibiotics harm super-bugs?
    (2 votes)
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