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Antibiotic Resistant Bacteria: Evolution & Examples

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

Learn about antibiotic resistant bacteria and how they evolved. We will look at some examples of antibiotic resistant bacteria that currently exist. A short quiz will follow in order for you to test your knowledge.

Bacteria and Antibiotics

The story of antibiotic resistant bacteria is really a tale of good versus evil. In this tale, the bacteria are most definitely the bad guy and the antibiotics are the good guy. While we would love for the good guy to win in every case, that's not always true when it comes to bacteria. Some of those little buggers are very persistent, contagious, and even deadly!

Antibiotics are given to treat bacterial infections.
Picture of antibiotics

You may already know that an antibiotic is a type of medication that the doctor may prescribe to you if you are sick and a strain of bacteria is suspected or confirmed as being the cause of your misery. In the majority of cases, in order for a patient to get rid of the bacteria that has infected their body, completion of a course of antibiotics is needed.

Sounds simple enough, right? Well, if you've ever been prescribed to take antibiotics, you might remember that they came with some rather specific instructions. In order to work, the entire course of antibiotics, or the whole schedule of pills, must be taken. Some doctors are rather explicit in emphasizing that 'even if you feel better,' you must take all of the prescription.

So how does all this related to our battle of good versus evil, life-saving antibiotics versus bad bacteria?

Antibiotic Resistance

Antibiotic resistant bacteria are strains of bacteria that do not respond to antibiotics. Instances of antibiotic resistance bacteria may occur on an individual basis or on a much larger scale. We'll touch on both.

Imagine that you are sick and your doctor has confirmed that bacteria are to blame. He prescribes an antibiotic. Once you start taking the antibiotic, you may start to feel better after a few days. At this point, the bacteria that caused your infection may have gone into a spore state. They're not dead, they're dormant. Bacteria go into this state whenever conditions exist around them that can kill them in their active or vegetative state. This transition to dormancy is what allowed the symptoms to stop and for you to feel better. With continued exposure to the antibiotics, the dormant bacteria would not be able to continue functioning and will die.

Bacteria go into spore form until conditions are favorable again.
Micrograph of bacterial spores

If you stop taking the antibiotics before the bacterial spores are killed, then the bacteria can return to their vegetative, or active, form. Just like our bodies are able to remember a previous infection so we can fight it off again, bacteria are able to remember an antibiotic to which they are exposed so that they know how to counteract it if exposed again. Once the bacteria is back to being healthy, it knows how to resist the antibiotic that you were taking. And thus, we have antibiotic resistant bacteria! Smart little buggers, aren't they?

Once bacteria becomes resistant to an antibiotic, they can no longer be killed by that particular medication. This is what causes resistance on an individual level. You will need a new weapon (a new antibiotic) to fight off your infection - and hopefully this time, you'll complete the whole prescription!

Evolution of Resistant Bacteria

Remember I mentioned that antibiotic resistant bacteria can be a problem on a much larger scale, as well? Here's where it gets ugly. Any bacteria that survive the infection will retain their resistance and pass it on to future generations of bacteria. And resistance can develop with any antibiotic! So it's possible for a particular strain of bacteria to become resistant to two (or more) different antibiotics. This can continue until this particular strain of bacteria becomes resistant to every antibiotic that exists. At that point, the strain of bacteria will be completely antibiotic resistant and we are left without modern medical weapons with which to fight it.

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