Bacterial Pathogenesis

in this video, we're going to begin our lesson on bacterial pathogenesis or how some bacteria can cause disease. And so the term pathogenesis is a term that refers to the process of disease development or infection inside of a host. And bacterial pathogenesis generally involves four important steps that will get to briefly discuss down below, but then go into more detail as we move forward in our course. And so the very first step of bacterial pathogenesis is going to be exposure to the pathogen. And so what that means is that the person like for example, dr clutch here needs to be exposed to the pathogen. And that exposure could potentially come from another infected person that may sneeze or cough or something like that and be exposed. So then after exposure, the second step is going to be adherents of the bacterial pathogen to the skin or mucosa. And adherence is a critical step for pathogenesis. If the back, if the pathogen cannot adhere then the pathogen will ultimately be eliminated from the body and they will not be able to cause disease. And so adherence is a critical step and they can adhere to our skin or mucosa, for example. And so here what we're showing you is the bacteria adhering to the mucosa, specifically to the mucus or mucus membranes. And so the third step is going to be uh invasion through the epithelium. And so in this process, the bacteria can actually make its way into the epithelium, the epithelial cells or these cells here that are on the border or perimeter and in some cases they may remain here. In other cases, they may make their way into the bloodstream or invade into a different type of tissue. And then the fourth step is going to be the multiplication of the pathogen, the replication of the pathogen inside of the host. And so you can see that over here, the pathogen is now multiplying and creating many identical versions of itself. And so at that point that would lead to signs and symptoms and dr clutch, starting to feel sick. And so we'll get to talk a lot more about each of these steps as we move forward. But for now this year concludes our brief introduction to bacterial pathogenesis. And again, I'll see you all in our next video.

in this video, we're going to talk about the first step in bacterial pathogenesis which is exposure to the pathogen. And so once again, the very first step in bacterial pathogenesis is going to be exposure to the pathogen or an encounter with the pathogen. Now it is important to note that not all exposures to the pathogen and not all encounters with the pathogen are going to result in an infection. And this is because the pathogen not only must it be encountered, but the pathogen must enter into the host tissues via what's known as a portal of entry. And so a portal of entry or portal of entries can be defined as specific locations where the host tissue cells are going to be directly in contact with the external environment, allowing a pathogen in the external environment to enter into the body. So examples of portals of entries include the skin, mucous membranes and parental routes, which is like the pathogen being directly injected into the body or the pathogen bypassing the skin and mucous and entering into the body via sites of broken protective barriers such as for example, cuts in our skin or open wounds and things like that. Now the most common portal of entry for pathogens tends to be the respiratory tract just being inhaled through our respiratory system. For example, the spread of COVID-19 is mainly going to infect using a portal of entry of the respiratory tract. And so if we take a look at our image down below, we can see that there's an image here focused on the exposure to the pathogen. And so what you'll notice here is that DR clutch is being exposed to the pathogen here when this infected person sneezes or coughs. And so you can see that the pathogen here is um again it's uh DR clutch is going to be exposed to these pathogens. Now again not all exposures are going to result in an infection. And this is because the pathogen does have to be able to enter via a portal of entry. Like for example perhaps DR clutches knows. And so over here what we're showing you is a zoom in of dr clutches nose. And so you can see that these microbes are entering via the portal of entry here. And so you can see these microbes are able to come in through the nose here through the respiratory tract. And so then you can see the pathogen is now within uh Dr clutches respiratory tract and is going to be exposed to the nasal mucous membrane. And so this year concludes our lesson on the very first step in bacterial pathogenesis exposure to the pathogen. And we'll get to talk about the other three steps of bacterial pathogenesis as we move forward in our course. So I'll see you all in our next video

in this video we're going to talk about the second step in bacterial pathogenesis which is adhesion to the host. And so after pathogen exposure and entry of the pathogen at the portal of entry the pathogen must then properly adhere to the host. And so adhesion is the ability of the pathogen to bind to host cells by using adhesion factors or adhesives. And so these adhesions are simply molecules on the surface of pathogens that bind to very specific receptors on the host cells. And so these adhesions can be found on bacterial pillai, february or flag. Ela. Now it is important to note that the adhesive receptor binding is actually very very specific and it is ultimately going to control the cell type that the pathogen will adhere to and the tissue that the pathogen will cause a disease in. And so um what this means is that a pathogen will only be able to cause disease if it has the appropriate adhesives to bind to very specific host cell receptors. And without these very specific adhesives then they will not be able to adhere and then they will not be able to cause disease. And so if we take a look at our image down below, what we can see is this is an image focused on adhering or adhesion to the host cell. And so notice once again we have our portal of entry we have our microbes entering via our portal of entry and which will notice is that there are two different microbes that are entering here. We have the green microbe entering right here and then we have the blue microbe entering right here. And so notice that here on the nasal mucous membranes again we have the green pathogen and then we have this blue microbe right here. And what you'll notice is that if we zoom in even further into this particular region and zoom in right here that the green pathogen has the appropriate Adhi since in order to bind to this very specific host receptor. And so these host receptors are down below right here and the adhesives are these little molecules that are sticking off right around here. And so because this green microbe has the appropriate adhesives to bind to the host cell receptors, it is going to be able to attach and adhere. And so notice that this microbe is saying success. However, notice that the blue microbe over here has different set of adhesives and because it has a different set of adhesives and adhesive receptor binding is very specific. This blue microbe over here is not going to be able to bind. So you can see the turn away arrow right here means that it will not be able to bind to the host cell receptors and that means that this microbe will not be able to adhere and it would not be able to cause uh an infection. And so notice it is saying I can't bind maybe this isn't the host for me. And so perhaps this microbe would need to make its way to a different set of cells who's um receptors are going to be compatible with these particular adhesives. But adhesion to the host is a critical step in bacterial pathogenesis. And this here concludes our brief lesson on this idea and we'll be able to talk about the other steps of bacterial pathogenesis as we move forward. So I'll see you all in our next video.

in this video, we're going to talk about the third step in bacterial pathogenesis which is invasion into the host cell or into the host tissues. And so once the pathogen has adhered to the host, it will then either find a way to invade to the inside of a host cell or just enter into the surrounding host tissues. Now, invasion of the inside of a host cell actually allows a pathogen to reduce competition for nutrients and even to hide in order to avoid the immune system and so invading to the inside of a host cell can be beneficial for the pathogen. Now uh the invasion into most types of host cells actually involves one of two potential mechanisms of induced endorse Itto sis and induced endorse itto sis is just when the bacterial cell is able to trick quote unquote host cells to perform endorse Itto sis or to endorse it toast. Even when that host cell typically would not perform endorse Itto sis. And so we'll get to talk a little bit more about this as we go along. But uh this induced endoscopy psychosis can occur via the pathogen coming into contact with epithelial cells and secreted effect er proteins that cause membrane ruffling and this membrane ruffling is going to occur with the cells acting which is part of the cells. Sido skeleton. Now the membrane ruffling can be defined as a rearrangement of the acting filaments and this rearrangement of the acting filaments in the host cell results in membrane ruffles and those ruffles are really just wrinkles that ultimately end up in closing the bacterial cell and bringing the bacterial cell into the host cell. And this resembles endo psychosis, but it's not quite exactly the same. And then the other way is just by standard endorse itto sis where the pathogen will express surface proteins that will ultimately bind to receptors on the host cell and then the pathogen will be engulfed and brought into the inside of the host cell. And so, if we take a look at this image down below, we can get a better idea of how this invasion of or invasion into the host cell can occur. And so what you'll notice is on the left over here, what we have are some pathogens that have adhered and on the right, what we have is pathogens that have invaded the host cells and which you'll notice is that here we're showing you two different pathways to get there. We have the top pathway here and then we have this bottom pathway in blue and they basically allow for the pathogen to invade inside the host cell. And so the first path that the pathogen could take is through a membrane ruffling And with membrane ruffling, What you can see is that the pathogen will secrete effect er proteins and the effect of proteins will be taken in by the host cell and those affected proteins ultimately will cause the acting filaments to rearrange in this membrane ruffling. And so you can see that the membrane is starting to wrinkle up and ruffle and ultimately, what ends up happening with this membrane ruffling is that the pathogen is going to be brought towards the inside of the host cell. And again, once the pathogen is inside of the host cell it is going to have less competition for nutrients, allowing it to survive and thrive better. And it will also be able to avoid the host cell's immune system or the host's immune system. And so it is advantageous or can be advantageous for pathogens to invade inside of host cells. Now, the other way that the pathogen could invade inside the host cell is through just being engulfed through regular endo silicosis. And so you can see here that the surface proteins here on the surface of the bacteria will bind to host cell receptors and then the host cell receptors upon binding to the bacterial surface proteins will induce standard endorse Itto sis and the pathogen is engulfed. And so the pathogen again makes its way into the host cell where it will have less competition for nutrients and be able to avoid the host cells or the host's immune system. And so ultimately what you can see here is that the the host cells have been invaded and the cells are now inside of the host cell and if they're not going to remain inside of the hotel, they can then continue to make their way into the host cell tissues. And so this here concludes our brief lesson on uh, the invasion of the pathogen into the host cell or the host cell tissues. And we'll be able to get some practice applying these concepts and then talk about the fourth and final stage of bacterial pathogenesis as we move forward. So I'll see you on our next video.

in this video, we're going to talk about the fourth step in bacterial pathogenesis, which is multiplication of the pathogen, or colonization of the pathogen inside of the host. And so after a pathogen enters into the inside of a host cell or enters into the hosts tissues, the pathogen will then begin to multiply or colonize inside of the host and begin damaging the host by causing an infection. And so pathogens can cause three types of infections that we have down below. Pathogens can cause local infections, focal infections or systematic infections. Local infections, as their name implies, are going to be infections that are confined to a relatively small area, a localized area of the body, usually near the portal of entry. Now, focal infections on the other hand, are typically going to start off as localized infections but then they spread to a different part of the body. And so what that means is that the focal infections will be able to uh basically cause an infection in multiple different areas of the body. And so they're able to spread to different locations of the body, usually by using the bloodstream. And then the third type is going to be the systematic infection, which is going to be characterized by an infection that disseminates or widely spreads throughout the entire body. And so it's not just going to be a few locations, it will be systemic or the entire body. Now, if we take a look at our image down below, What you'll see is that we're focusing on the colonization of the host. And so again, on the far left over here, what we have is a local infection. And again, the local infection is going to remain relatively within a small area of the body. And so for example, if there is a cut, the pathogen may enter via the cut and again it is going to multiply and colonize this specific region of the body without spreading if it is a local infection, now, the next type that we have here is going to be the focal infection. And the focal infection may start off as a local infection, but then it will spread to a different area of the body. And so for here in this example, we're showing you an infected tooth cavity that may have specific microbes in it. Uh and then these microbes may be able to travel to a different location of the body and that could lead to perhaps endo card endocarditis, which is infection of the hearts lining and valves. And so here with the focal infection, notice that it is capable of spreading to a different region of the body. And then last but not least over here on the far right, what we have is a systematic infection. And with systematic infection as its name implies, the entire body is going to be infected. Like for example, bacteria anemia is when there is bacterial infection of the blood and the blood spreads throughout the entire body. And so it is called a systematic infection if it's spread throughout the entire body. And so this year concludes our brief lesson on the multiplication or colonization of the pathogen inside of the host, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.