The medical world can be a confusing place. Patients and their families might feel overwhelmed by the large vocabularies and complicated explanations they get from their health care providers. Students entering health care also struggle to grasp the complexity of health sciences, and are forced to memorize huge amounts of information. We hope to make understanding the medical world a bit easier. Look around! These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you have read or seen in any video.

Antibiotics overview

Antibiotics are a type of medicine which are used to treat bacterial infections.

Everyday 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 is 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).

Bacterio-static vs bacteri-cidal

Just to be clear, antibiotics don’t affect virusesfungi, 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.

Parasites, viruses, and fungi are not affected by antibiotics

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. 

Alexander Fleming in his lab

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, almost 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.

Timeline of antibiotic class discovery

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.