The History, Development & Impact of Antimicrobial Resistance

Instructor: Bridgett Payseur

Bridgett has a PhD in microbiology and immunology and teaches college biology.

Antimicrobials have been a boon to humankind, helping protect us from a variety of infections. Unfortunately, they're becoming less and less effective. Read on to learn how antimicrobial resistance developed, and what it means for us.

Antimicrobials and Antimicrobial Resistance

It is a constant arms race between medicine and microbes. Once humans develop a medicine to fight infection, the microbe develops armor to protect itself.

A significant number of human diseases are caused by microbes, tiny organisms that are too small to see without a microscope. Microbes can include bacteria, viruses, protists, and fungi. These are all different types of organisms, and so different antimicrobials are used to fight them.

The first antimicrobials used were antimalarials. Specifically, the first antimalarial was quinine, which is an extract from the quina-quina tree. It was possibly discovered by indigenous people, and later used by Jesuit missionaries in the 1600s.

Today, antibiotics are used to treat bacterial infections. You've probably heard the story of Alexander Fleming, who dropped a piece of moldy bread into his petri dishes and serendipitously discovered penicillin. A lot of antibiotics are actually derived from fungi or plants, which have made them as part of their defense system.

Antivirals are probably the most recently developed antimicrobial agent. As the name implies, they fight viruses. Antivirals tend to be specific against a certain type of virus, for example targeting influenza, HIV, or herpesvirus. They act by inhibiting the viruses' ability to be replicated, stopping the infection from spreading.

How Did Antimicrobial Resistance Develop?

We have medicines that can fight malaria, bacteria, and viruses. That's great! Problem solved! Right?

Unfortunately, no - the problem is not solved. Microbes are very adaptable. They can develop ways to survive different circumstances, including developing antimicrobial resistance.

Antibiotic resistance developed almost immediately after penicillin began being widely used. Certain strains of bacteria developed a protein that could inactivate the penicillin, making it useless.

Many malaria strains are developing resistance to antimalarials, as well. Quinine is not used often anymore, since most strains of malaria are resistant. Newer antimalarials are also becoming ineffective, due to the development of antimalarial resistance.

Many viruses have also developed antimicrobial resistance. Viruses mutate rapidly, and can develop beneficial traits that make antivirals ineffective.

So how did antimicrobial resistance first develop? When a patient takes an antimicrobial, such as penicillin, it begins to kill off the bacteria. The weakest, most susceptible bacteria will die first. The stronger, more resistant bacteria will die later.

If a patient stops taking his antibiotics before the stronger bacteria have died, he will be left with a more resistant population. These bacteria will replicate, and might mutate to become even more resistant. Eventually, only the most highly-resistant bacteria will be left, and the penicillin will no longer be effective. This patient can then pass on his resistant bacteria to others.

The image shows how resistant bacteria can continue to thrive and grow, even when susceptible bacteria are killed off.
antibiotic resistance

This same process happens when antimicrobials are misused for viruses, parasites, and fungi. When we say an antibiotic is misused, we mean that either the patient doesn't follow the doctor's directions, or that antibiotics are used when they are not necessary. Taking antibiotics for viral infections, such as a cold, or giving antibiotics to livestock when they aren't sick, are both examples of misuse that can lead to resistance.

What Impact Does Antimicrobial Resistance Have?

As you can imagine, antimicrobial resistance is a big problem. Since the late 1930s, we've relied on antibiotics to cure us of bacterial infections. Now, however, there are bacteria that are resistant to some or even all of the antibiotics we have available. Some strains of tuberculosis-causing bacteria, for example, are resistant to first, second, and even third lines of antibiotics.

Methicillin resistant Staphylococcus aureus (MRSA) has become a huge problem in hospitals. It can infect the skin, generally around areas that have been compromised due to medical procedures. It is so common that patients are spreading it beyond hospitals, into the community.

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