Microbiology, part 30: Growth - Microbial Growth Requirements

Hi. I'm Cathy with Level Up RN. In this video, we'll be discussing biofilms and quorum sensing. And at the end of the video, I'm going to give you guys a little quiz to test your understanding of some of the key facts I'll be covering, so definitely stay tuned for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcards on biofilms and quorum sensing so you can follow along with me, and pay close attention to the bold red text on the back of the cards because those are the things that you are likely to get tested on.

A biofilm is a community of microbes enclosed in an EPS matrix that forms a slimy layer on a surface. So EPS stands for extracellular polymeric substance. Examples of biofilms include plaque buildup on the teeth, as well as the slimy layer that forms on a shower that has not been cleaned in a while. So biofilms play a significant role in infectious disease and medical-device-related infections. So let's talk about how biofilms form and some key characteristics of biofilms.

Biofilms form when planktonic cells, which are free-floating microbes, attach to a surface and become sessile or unable to move freely. These microbes then grow and divide and produce an extracellular polymeric substance. And then as the biofilm matures, water channels develop, which allows for the transport of nutrients and the removal of waste products in the biofilm. And then cells along the edge of the biofilm can slough off to colonize new sites, which starts the process all over again. Having this close-knit community of microbes provides an optimal environment for the exchange of genetic material between the cells, such as genes that code for antibiotic resistance. In addition, biofilms allow for metabolic collaboration between the microbes in the biofilm. For example, the waste product of one microbe often becomes the nutrient for another microbe. Biofilms also provide protection from environmental hazards, such as antibiotics, because when you have a big amount of microbes, the microbes on the bottom are going to be protected from those hazards.

And then finally, biofilms allow for quorum sensing, which is something we're going to talk about in detail now. Quorum sensing is a form of cell-to-cell communication that allows bacteria to turn on group behaviors once the population reaches a threshold density. So it's kind of like a flash mob that goes into rob a store. If a couple of dudes go in to steal stuff from the store, then chances are they're going to get caught, and they're not going to make it out of the store with any stolen goods. However, if a big group of criminals goes into the store at once, then that is going to overwhelm security, and chances are, at least some of those criminals are going to make it out of the store with stolen goods. So it's just like that with bacteria. A small number of bacteria are not likely to overwhelm a host. But if they wait to make their move until there is a big group of bacteria, then chances are they have a shot at making it past the immune defenses of the host.

Here is basically how quorum sensing works. So bacteria in the biofilm produce small molecules called autoinducers, which are blue circles in the image. When the bacterial population reaches a certain threshold, which is called a quorum, then those autoinducers bind to receptors in the bacterial cells. This binding triggers the transcription of genes that code for virulence factors, such as toxins or exoenzymes, which are the red circles in the image. So the bottom line is that quorum sensing allows bacteria to only synthesize virulence factors when the population is big enough to overcome the immune defenses of the host.

All right. It's quiz time, and I have three questions for you. Question number one, a biofilm is a community of microbes enclosed in a blank. The answer is extracellular polymeric substance. Question number two, biofilms form when planktonic cells become blank. The answer is sessile. And question number three, blank is a form of cell-to-cell communication that allows bacteria to turn on group behaviors once the population reaches a threshold density. The answer is quorum sensing.

All right. That's it for this video. I hope it was helpful. Take care, and good luck with studying.

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In addition, biofilms allow for-- but if they wait to make their move until there is a big group.