Opportunistic Infections from Antibiotic Usage: Definition & Examples

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  • 0:05 Opportunistic Infections
  • 1:09 Yeast Infections
  • 2:35 Antibiotic-Associated Diarrhea
  • 3:38 Probiotics
  • 4:36 Lesson Summary
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Lesson Transcript
Instructor: Katy Metzler

Katy teaches biology at the college level and did her Ph.D. work on infectious diseases and immunology.

In this chapter, we've learned about all kinds of antibiotics and how great they are at curing bacterial infections. However, there is also a bad side to antibiotic treatment. In this lesson, learn how antibiotics can actually cause opportunistic infections.

Opportunistic Infections

Imagine you are the youngest child in a family with five children. Most of the time, your older brothers and sisters eat all the cookies and get the best spots in front of the TV when it's time to watch a movie, and they always make you sit in the middle seat in the car. It is hard being the underdog, huh? And you'd take any opportunity to improve your situation, wouldn't you?

Well, it turns out that bacteria are not so different than siblings. In our bodies, we have normal flora, the beneficial bacteria and other microorganisms that naturally live on and inside of us. They're kind of like older brothers and sisters; they are very protective of their territory and won't let pathogens take hold. However, sometimes the normal flora can be weakened - for example, by antibiotic treatment. If the normal flora let their guard down, pathogens can take the opportunity to set up an infection. Conveniently enough, this is called an opportunistic infection. In this lesson, we'll learn about two examples of opportunistic infections that can come from antibiotic usage.

Yeast Infections

Many of you women watching this video may be familiar with this topic. It's pretty common for women to get yeast infections after a course of antibiotic treatment. Let's look at the reason why. In a normal, healthy vagina, there is a complex community of microorganisms called the normal vaginal flora. The most abundant type of bacteria is Lactobacillus acidophilus, or L. acidophilus.

L. acidophilus produces lots of lactic acid as a part of its day-to-day life. Lactic acid is, well, acidic, and most bacteria can't survive in acidic conditions. L. acidophilus, as you can see from its name, is an acidophile, meaning that it loves acid. But pathogenic bacteria, as well as the fungus Candida albicans, a type of yeast that commonly lives on our skin, don't feel at all at home in the acidic environment produced by the normal vaginal flora. So L. acidophilus does a great job of protecting women's vaginas by producing chemicals that harm pathogens - until antibiotics come into the picture.

If a woman gets an infection and needs to take antibiotics, they can kill the population of L. acidophilus that lives in her vagina. This provides an opportunity for Candida to come in and set up house, causing a yeast infection. This kind of opportunistic infection is also called a superinfection because it's an infection that occurs after or on top of another infection, the original one that made the woman need antibiotics in the first place.

Antibiotic-Associated Diarrhea

Vaginas aren't the only place in our bodies that are colonized by normal flora. Our intestines are also chock-full of good bacteria that are beneficial for our health and digestion. In fact, our gut microbiota, as the normal flora of the intestines are called, consist of trillions of bacteria that form a very complex ecosystem with more than 400 different species. Wow. We are just one species, and there are 400 microbial species just in our intestines? Amazing.

Anyway, the gut microbiota protects us from intestinal pathogens by taking up the space and nutrients in our gut, basically elbowing out any potential pathogens. But when we take antibiotics, our gut microbiota can be killed off, leaving plenty of room for pathogens to take hold. The opportunistic intestinal infections caused by antibiotic treatment are called antibiotic-associated diarrhea, or AAD. The bacterium Clostridium difficile, known as C. diff for short, can cause particularly severe cases of AAD.

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