Lecture 10 - Infectious Organisms

追加: 2026-05-14

[00:00:00]hi everyone welcome to your final lecture of the course this week our focus is going to be on both bacteria and viruses that are capable of causing infections within humans there are certain types of bacteria that exist in our bodies and on the surface of our skin that are symbiotic and a symbiotic relationship is one where the host which would be us as well as the specific organism the bacteria are mutually beneficial to one another and the following are a list of ways in which our normal bacterial populations are capable of providing us with a variety of different benefits and here you can see a cross-section of our gastrointestinal tract symbiotic bacteria live within the large intestine specifically within the inner lumen our normal bacterial flora exists within there our normal bacterial flora are also responsible for aiding us in digestion and the production of both vitamin k and b vitamins within our large intestine they help to maintain that mucosal layer the inner mucosal layer made up of epithelial tissue and are also capable through metabolic processes of releasing important minerals such as magnesium calcium zinc and iron from the food that we ingest now having a healthy bacterial flora within your gastrointestinal tract can also play a huge role in helping to prevent a number of different cancers colon prostate as well as breast and then as we already know they're responsible for producing lactic acid during fermentation remember glucose is an anaerobic process we do not require oxygen in order for glycolysis to take place as a result of glycolysis where we break down glucose we produce a little bit of atp and end up with pyruvate as the by-product now in humans because we are aerobic in the presence of oxygen pyruvate goes through pyruvate oxidation then the krebs cycle and finally the electron transport chain where we produce an abundance of atp remember in an anaerobic environment where there is no oxygen or for specific prokaryotes such as bacteria who are incapable of aerobic respiration they utilize fermentation to be able to recycle that pyruvate to recycle the nadh molecules into their oxidized form and in the process producing lactate also known as lactic acid now since the bacteria in order to survive are producing an abundance of lactic acid wherever bacteria are located they are also going to be producing a lower ph environment so an acidic type of environment in other pathogenic species bacterial fungal species they are not going to thrive in acidic environments and so as a result the symbiotic bacteria that exist both within our bodies and on the surface of our bodies they produce that acidic type of environment that provides us with a very basic protective immune support now our bacterial flora are also responsible for being able to produce short chain fatty acids and there are a number of different physiological processes that short chain fatty acids are very beneficial in and ways in which we can help support our normal bacterial flora are through probiotics or even prebiotics right if you look on an activia yogurt container you're going to see probiotics as their marketing tool right within that yogurt culture you have symbiotic bacteria that when ingested are going to help to now we can also help to support those bacteria by ingesting prebiotics and with fiber bacteria are capable of breaking that down through anaerobic processes of fermentation and as a result are able to produce short chain fatty acids so the normal bacterial flora that we have they're capable of converting these complex carbohydrates into the short chain fatty acids so that those short chain fatty acids can then be absorbed by our bodies and used for energy production and one of the places that's short chain fat and one of the places that short chain fatty acids are utilized in the body are in the brain to help regulate brain function so as a result of research they've been able to link a lack of a normal healthy bacterial flora within your gi to various mental health disorders such as depression and anxiety now as a quick recap remember here we're looking at our prokaryotic cell remember a bacteria is the example of the prokaryote that we were looking at so as you'll remember all cells contain a plasma membrane right that plasma membrane is separating the internal environment from the external environment surrounding the plasma membrane bacteria also have a cell wall and beyond that they have a protein coat this protein layer that surrounds them known as the capsule extending from the capsule they can either have various extracellular extensions such as the flagella or even cilia now the ones that we're seeing here in this image those are the pili and those are those small outgrowths that allow for bacteria to be able to exchange dna with one another through the process of conjugation now we have two main groups of bacteria that we can classify them into and those are gram positive as you can see here on the left and gram negative as you can see here on the right now this classification of gram positive or negative comes from a specific type of staining known as gram staining and so when you take a bacterial culture and you apply that specific stain to that culture they are either going to absorb that stain and so will be a certain color or will not absorb that stain and the reason that they will either absorb the gram stain or not is based on the thickness of their peptidoglycan layer that you can see is much thicker in our gram positives and much thinner in our gram-negative bacteria now most bacteria fall under the gram positive classification and in this case here they have their plasma membrane and outside of the cell membrane they are encased by a peptidoglycan layer which is their cell wall as you can see within that cell wall they have a number of embedded proteins as well as lipopolysaccharides and in contrast the gram negative has a very thin peptidoglycan layer that is then covered by an outer membrane made up of phospholipids that contains lipopolysaccharides now because the peptidoglycan layer is much thinner in gram-negative as well as the presence of this outer membrane they do not readily absorb gram staining and so as a result if you were to look at a population of gram positive bacteria they are going to absorb the gram stain which is bluish in nature and so if we were to take a culture of bacteria in a petri dish allow that culture to grow and apply the gram staining you would then see either that they would absorb the stains such as integram positives or they would not absorb the gram staining and so here you can see with the gram positives they have absorbed that gram staining which makes them appear purple and then in this population of gram-negative bacteria they have not absorbed that gram staining and as a result they look pink and to give you another perspective here looking at the differences between your gram positives as well as your gram negatives in the gram positives we have a very thick peptidoglycan layer that is capable of absorbing that gram staining and here in the gram negatives we have that outer membrane covering the very thin peptidoglycan layer sandwiched between both outer and inner membranes now on our youtube channel i have included a video so that you can see how a bacterial cell is capable of producing an endospore which allows that bacteria to be able to protect all of its genetic material under very harsh conditions during you know periods of environmental stress this is another adaptation that has allowed bacteria to be able to become highly resistant to environmental stresses when compared with many other microorganisms what ends up happening is the bacteria under very harsh conditions form this very thick walled endospore here in this diagram you can see the bacterial cell that has now formed this spore coat in addition to an outer layer known as the exosorium and so the bacterial cell now has ensured that at the core all of its genetic material is going to be protected and well maintained the main goal of forming the endospore is to protect the genetic material of that bacteria and allow it to withstand the harsh environmental stresses that it may be under until those stresses are removed and so endospores can remain dormant for months or even years at a time now there are different types of bacteria and we can classify them based on the shape of their cells we have those that are spherical in nature we have those that are rod shaped and then those that are spiral shaped bacteria that maintain a spherical shape are known as cocci those that are rod shaped are known as bacilli and those that are spiral shaped are known as spirochetes now in population the cockeyed bacteria arrange themselves in different patterns so we have pairings of caucai which are known as diplococci we have clusters of cockai known as staphylococci and then those that arrange almost linear chain lengths of cockey bacteria which are known as streptococci so if you were to take a look at any spherical type of bacteria you would be able to define which type you're looking at based upon its arrangement of the different bacterial cells in population now in the evolution lecture we discussed the idea of microevolution with the example of antibiotic resistance so if you recall here antibiotics are acting as a bottlenecking event what does that mean we have a population that is going to have some event that is going to cause a severe reduction in the population size and so what ends up happening with any bottlenecking event is that the proportion of specific alleles in that original population are going to be drastically different from the subsequent population post bottleneck and so what can happen is in a population of bacteria there may be some that possess specific alleles that allow them to be highly resistant to specific types of antibiotics now once those antibiotics have been taken for that full length of prescription the population size is going to experience a huge bottleneck and what will happen after antibiotics have been taken is that the highly resistant bacteria will be more likely to survive and when they do they are going to be the ones that reproduce through binary fission and so we end up with a population of primarily highly resistant bacteria and so this is a problem with the over prescription of antibiotics we're actually speeding up the selection process where we are allowing the highly resistant mutations of resistant alleles to become the most abundant allele in the population and so we have the potential there of creating that super bug now antibiotic resistance is not only an issue because of the over prescription of humans but also farm animals right and so if all farm animals are being administered prophylactically antibiotics in order to protect the herd we can see here we are providing an environment in which we are going to be more susceptible to developing these multi-resistant superbugs and one of the ways in which we over prescribe for the human population is for those that present with cold and flu which as we'll learn later are viruses antibiotics are not capable of dealing with a viral infection they can only deal with bacterial infections so as a result we're over prescribing antibiotics as a result of individuals having viral infections but being unable to determine one over the other so here in this diagram we have the antibiotic identified here by this upper image almost looks like a bullet okay and then the enzyme identified by the more square type of structure here so some of these resistant genes provide bacteria with the ability to produce specific enzymes that are capable of breaking down the antibiotic so ultimately the antibiotic is administered it's taken into the bacteria but the enzyme that they contain either allows for the modification of that antibiotic which essentially will make it inactive or to simply break it down and with modifying them the enzymes are modifying them so that they are harmless to the bacteria some of the genes as well code for membrane proteins that have adapted to be able to simply excrete the antibiotics so once it's been taken in by the cell the antibiotic simply will be pumped out of the cell and when the antibiotic can effectively bind to the enzyme and block its activity the bacterium is unable to live and so they've also been able to adapt a few other strategies whereby they're able to alter their target sites and when they do so they're able to produce those enzymes with altered target sites so that ultimately the antibiotic is unable to bind to the enzyme and inactivate it this is another diagram that i've included here to give you just a different visual but ultimately it all comes down to the same information that we just discussed previously and so they have the ability to increase membrane proteins that are able to actively pump out the antibiotic they're able to inactivate the antibiotic make their cell walls impermeable by modifying the proteins of their cell walls and also modifying the enzyme binding sites itself so those with chance mutations that have occurred that have altered the binding site those individuals are the ones that are more resistant and so they are able to survive reproduce and pass on their dna to that next generation now there are a number of organisms that are opportunistic in nature and these are those that are going to cause infections when our immune system is somehow suppressed or when the normal flora of bacteria has somehow been damaged so say you have strep throat and you want to take an antibiotic to kill that bacteria well the antibiotic is going to work systemically and so you're not only going to wipe out the pathogenic bacteria causing the infection you're also going to be impacting your normal healthy bacterial flora and this is where sometimes after antibiotic treatments patients can experience other types of infections such as fungal infections and opportunistic infections can be caused by any of the various groups of microorganisms we're not going to be looking at fungi or parasites this semester but bacteria and viruses are equally capable of producing opportunistic infections so as i mentioned these opportunistic infections are going to occur as a result of some sort of suppression or alteration of our immune system and so any situation in which that's going to happen we will be more susceptible to opportunistic infections and so some individuals are genetically predisposed chemotherapy is going to wipe out both good cells and bad cells so that can also suppress your immune system patients living with hiv infections they are immunocompromised so as a result they can also be susceptible to opportunistic infections those with bone marrow diseases remember your bone marrow is responsible for producing your abundance of white blood cells and those white blood cells are responsible for being able to provide us with immune support pregnant patients as well are susceptible to opportunistic infections individuals with autoimmune diseases who are on immunosuppressant medications to try to suppress the immune response so it's not attacking their own cells they are also susceptible to opportunistic infections and so we're going to be spending some of our time right now taking a look at some of the most common types of pathogenic bacteria so these are bacteria that are capable of producing infections when they are allowed to grow in abundance within our bodies so the first type is known as mrsa and mrsa stands for methicillin-resistant staphylococcus aureus so there's a lot of information that you can take just from this name in itself methicillin is a type of antibiotic so this type of infection is resistant to that specific antibiotic staphylo if you recall from our previous diagram staphylococcus is referring to the cluster of spherically shaped bacterial cells and mrsa is capable of producing what is known as necrotizing fasciitis which is also known as flesh-eating disease and so typically it's the epithelial tissue that's going to be impacted originally and so external skin wounds can be susceptible to developing a mrsa infection as well as the inner linings of your respiratory as well as urinary tracts and immunosuppressed individuals so ultimately what we have here is an overgrowth of staphylococcus usually acquired in a hospital type setting and when localized to the skin can cause necrotizing fasciitis which is fleshing disease now vancomycin resistant enterococcus enterococcus is a type of bacterial infection this is a specific type of bacteria that are resistant to another type of antibiotic now the tissue infected here in this case is usually the small intestine or the urinary tract and typically again we're looking at an immunosuppressed patient right so a hospitalized patient who is taking antibiotics for some reason so remember antibiotics are going to kill the protective bacterial flora and ultimately are going to allow the enterococcus population to be able to overgrow and to spread and that's what causes the infection so i want you to take a look here at the gram staining method that has been utilized so we've applied gram staining here and so we could classify these bacteria as gram positive because they have taken on that purplish appearance which means that their peptidoglycan layer has absorbed the gram stain and we see that in the gram positive bacteria with chlamydia trigonatus typically the genitalia as well as the eyes can be infected it's the most common sexually transmitted infection and is known as a silent type of sti because a lot of patients can be asymptomatic now here in this diagram you're seeing the inflammation of the cervix now as this bacteria can affect the female cervix causing cervicitis which is inflammation of the cervix due to bacterial infection it can then spread further along the reproductive system infecting one or more of the upper reproductive organs so this can include the uterus fallopian tubes and even ovaries and so ultimately that can result in pid pelvic inflammatory disease and because it affects the upper reproductive organs it can lead to infertility now during childbirth the fetus is going to be exposed and ultimately this bacterial infection of chlamydia can be passed on to the child during the child birthing process nesteria gonorrhea more commonly known as gonorrhea typically affects the genitalia but also mouth and throat so if you're looking for the difference here the chlamydia is most common sexually transmitted infection it's affecting the genitalia as well as the eyes typically causing conjunctivitis with gonorrhea it typically affects both genitalia but also mouth and throat now with gonorrhea women tend to be asymptomatic whereas with men they tend to experience both burning during urination as well as discharge now again because this can affect the upper reproductive structures in women it can also cause pelvic inflammatory disease and be passed on to the baby our next pathogenic species of bacteria we're going to look at are the streptococcus pyogenes remember pile refers to pus and streptococcus is referring to the cocky bacteria that arrange themselves in a linear pattern now streptococcus pyogene these are the bacteria that cause strep throat so tissues affected most commonly the pharyngeal region of the throat and most oftenly affecting the tonsils when streptococcus pyogenes affects the skin this can also cause necrotizing fasciitis and then lastly streptococcus pyogenes is capable of infecting our blood this is why when you have a strep throat infection you must go on antibiotics to ensure that you kill that bacterial population the symptoms of the strep infection will eventually subside on their own and sometimes patients will go without taking antibiotics for this infection when they do that the bacteria are given enough opportunity to be able to invade deeper into the tissues and ultimately into the bloodstream when they pass through the bloodstream they end up in the heart and there they can end up damaging the heart valves we're going to learn more about the heart valves and look at rheumatic heart disease later next semester when we look at the cardiovascular system classic representation here of that white exit on the surface of the tonsils is highly indicative of strep throat and if left untreated streptococcus pyogene bacteria are capable of passing through the bloodstream and impacting the heart valves e coli these are actually a normal bacteria that occur in the large intestine so they are part of our normal bacterial flora and not only us but the entire animal kingdom contains e coli within their large intestines the problem is when you ingest a high amount of e coli due to some sort of contamination with food this then once in the stomach and the small intestine causes food poisoning all right so it's the presence of the e coli within the stomach and the small intestine that actually cause that e coli infection right e coli within our large intestine are symbiotic right they are beneficial to us and so they are present in our fecal matter but they are also present in the fecal matter of other animals and so when farmers are using manure to say spray a crop of romaine lettuce and that romaine lettuce does not properly get cleaned before you ingest it this is where you can end up with e coli contamination with a lot of your fruits and vegetables signs and symptoms of e coli infections would be diarrhea as well as vomiting because our body is just wanting to get rid of the excess so with vomiting that's the way that we're trying to get rid of it from our stomach up and out and with diarrhea we've essentially shut down the ability to absorb water in our large intestine to flush the large intestine and hopefully clear out as much as possible now with salmonella large amounts of salmonella can cause food poisoning as well and with salmonella this typically will cause diarrhea and vomiting within hours and typically unless you're immunocompromised or you're a child no treatment is needed except for just dealing simply with the side effects of diarrhea and vomiting the most common cause of traveler's diarrhea are campylobacter jejuni jejuni refers to the second portion of the small intestine which is where that would typically have their impact typically you're going to see signs of diarrhea maybe vomiting within hours to one day even after eating contaminated food typically with salmonella you're going to be experiencing diarrhea and vomiting within hours so relatively quick response whereas with a campylobacter juni infection individuals are going to see that even up to one day afterwards so you're on vacation and hygienic practices are not what they are here you can end up with person-to-person transmission by simply not washing your hands properly with mycobacterium tuberculosis this is the bacteria that is responsible for causing tb known as tuberculosis and so here you're seeing different stages of a tuberculosis infection tuberculosis impacts the lungs and is transmitted by airborne particulate we utilize the tb skin test to be able to diagnose and symptoms are going to include blood tinge sputum which is essentially phlegm that you would be coughing up fever as well as weight loss and there are multiple antibiotics that are taken as part of a cocktail to be able to treat mycobacterium tuberculosis infections because they are highly resistant to antibiotics and so what you see here is when the infection initially occurs you can see it almost is like a seed within the lung and as the infection spreads it starts to impact the alveoli that make up those smaller portions of the lung and as the tuberculosis infection continues to occur the individual ends up with these almost cavity-like structures within their lung tissue and so your ability to be able to take in oxygen and have it readily diffused into your pulmonary capillaries is going to be significantly hindered this is the bacterium that produces tetanus right this is why we all get our tetanus shot and clostridium tetani affects the central nervous system now i should mention it's not the bacteria itself that's affecting the central nervous system but a toxin that they produce that causes tetanus to occur okay and tetanus is a state of continuous contraction of muscles within the body and one of the common ones affected are the muscles of mastication which cause a syndrome known as lockjaw typically clostridium tetani is passed on by some sort of deep puncture wound so now the second half of this lecture we're going to be taking a look at viruses now if you recall viruses are non-living because they do not possess all of the criteria to classify them as a living organism and this gives you an idea to the actual size of some of these different viruses all right smallpox virus tobacco mosaic virus the bacteriophage polio caused by polio virus so you can see compared to even our red blood cell very small in nature but can have such detrimental impacts as we've seen with kobit 19 this past year viruses are considered non-living because they possess only a portion of the properties of living organisms so one of the keys is they do not have a cell membrane or possess membrane-bound cellular organelles with viruses the hereditary material can either be dna or rna remember in humans rna is utilized for a temporary transcript of our dna molecule right so all of our hereditary material is stored as dna with viruses they can be either dna viruses so have double stranded nucleic acid or they can be rna viruses so very diverse and then this is the most important viruses are unable of being able to replicate outside of a host cell if a viral particle of covid19 was to enter into your respiratory tract it would then try to invade one of your epithelial cells that lines the inside of your respiratory tract once inside our immune system has a hard time being able to locate it so it's capable of hijacking our own cells using our own machinery to replicate its dna we're going to take a look at the virus life cycle which shows you that there is a period of time where it's inside replicating and then there's a period when it then destroys our cells during its lytic phase where it then moves on to infect other cells in our body something unique about viruses as well is that they are very specific to specific cell types and so certain cells have certain receptors that that virus can only bind to now hepatitis for example impacts our liver cells the hepatocytes and so there are specific receptors on the hepatocytes that allow for hepatitis to be able to bind to those specific cells viruses also sometimes combine to similar receptors across multiple species and that gives us zoonotic types of infections and so swine flu bird flu yes but also covid right these are the ones that have a higher rate of evolution because they have a higher mutation rate and are more likely to cause pandemics which we have found ourselves in this past year and so with covid19 in and of itself is not a confection which they discovered was passed on from bat populations to humans viruses also contain various structures to them we have helical viruses polyhedral envelope viruses such as hiv and as well the bacterial phage if you recall the bacteriophage possesses all of its dna up in this head region here remember this is all protein all of the green material that makes up a virus is protein the bacteriophage is capable of being able to pass on its dna into a bacterial cell where it then is going to be able to utilize the machinery of the bacterial cell to be able to replicate this is another way in which the bacteria are capable of incorporating that genetic material into its own dna structure to increase their own genetic variability viruses need a host cell in order to infect the individual and replicate and we're going to take a look at these two cycles both the lytic cycle and the lysogenic cycle so the lysogenic cycle this is where the viruses dna has been incorporated into our own cell or a bacterial cell in this cases here we are looking at a virus that has been able to pass on its dna to a bacterium in this case and if this were one of our own cells say an epithelial cell we would just see that we had linear dna that it would be incorporated into the virus attaches to the cell membrane it is then going to eject its dna into the bacterial cell and then that dna is going to incorporate itself as part of the bacteria's dna and then as the bacteria then goes through binary efficient now we have two copies and so you can see here during this lysogenic phase this viral dna is going to be replicated at the rate at which this bacteria is capable of replicating then at some point the bacterial dna is going to be excised or removed from the bacterial dna or just host dna and ultimately then that viral dna is going to start to code for all of the protein components that make up the new viruses and so we can see here you have the lysogenic phase feeding into the lytic phase and during this lytic phase we have the protein coat being created from the viral dna to ultimately then assemble new viruses and then the virus-encoded enzymes that they can release will break down the host cell wall killing the host cell and then releasing the virus into the extracellular environment so whether it's a bacterial cell that they're infecting or whether it's one of our own cells the viruses are going to be going through this lysogenic cycle to be able to replicate their dna and then they will enter into a lytic cycle where the new viral particles are going to be able to be assembled so that they can ultimately produce enzymes that break down the host cell wall where they then are going to break out of that cell wall destroying the host cell in the process and enter into the extracellular space this is why when you have some sort of viral infection that causes a sore throat you're experiencing the redness and the inflammation that you do because the viruses have infected your epithelial cells in your throat and then during their lytic cycle they're then going to be breaking apart those epithelial cells causing that trauma which we then see as redness and inflammation now these cycles can be broken down into a number of stages during the lytic cycle here we have first off the attachment stage where the protein on the virus capsid is going to bind to the specific receptor here on the cell membrane then infiltration is going to take place where the host cell is going to take up the dna of that virus the virus will then go through replication where it will then replicate all of the dna and start to form the new parts to make up those new particles ultimately forming the new particles assembling the new virus so that the virus can be active ultimately secreting those enzymes and destroying that cell now with the lysogenic cycle you can have a virus either move through just the lytic cycle originally or move into the lysogenic stay there for a while and then finally back into lytic with the lysogenic cycle ultimately the virus that has infected the human cell is going to be integrated into the host chromosome so then that integrated chromosome is going to then be replicated with each cell cycle that occurs so within bacteria that's going to be really quickly within our own cells not so quickly but during this cycle the virus is going to remain hidden from our own body's immune cells from the b lymphocytes t lymphocytes all of those other white blood cells that are looking around for infections the t lymphocytes are eventually going to be capable of being able to detect changes but by that point typically the virus has already broken down the cell and destroyed it now as i mentioned we can have rna viruses and we can also have dna viruses viruses that contain rna instead of dna have to convert that single stranded rna molecule into a double-stranded dna molecule before it can replicate within the host cell because remember how on earth could you take an rna molecule and simply add it into our dna sequence right you can't and so with rna viruses they have to go through this process of reverse transcription there's an enzyme known as reverse transcriptase that they utilize to be able to add on the complementary base pairs to be able to form the double stranded molecule the problem is there's no proofreading that takes place and so while the virus is creating that double-stranded molecule so that it can be inserted into our own dna there are a number of different substitution errors that could occur along the way and there's no way of catching those and so as a result rna viruses are able to mutate really rapidly because of the mistakes made when trying to create that double stranded dna molecule and so because they mutate more readily they become so much harder for us to be able to treat because now they're going to be producing completely different proteins to identify them completely different dna sequences ultimately as well and we're going to look at the entire cycle of our dna polymerase allowing us to replicate our dna and then we're also going to look at how we then take that copy of our dna to produce our rna right in both of these cases our enzymes possess proofreading ability but the viruses reverse transcriptase enzyme converting from the rna back to the dna does not possess the ability to proofread in and of itself is going to be advantageous to the virus because now it's capable of mutating very rapidly so some examples of rna viruses we have hiv influenza sars hepatitis as well here you can see measles and an individual here that has suffered from polio infection now we're going to take a look here at the human immunodeficiency virus the reason that hiv has been such a problem for so long is that it infects certain types of white blood cells within our bloodstream and the white blood cells are our immune cells and so we're relying on our immune cells to be able to provide our bodies with protection but with hiv this virus is capable of actually infecting our own lymphocytes now hiv primarily infects a specific type of t lymphocyte known as cd4 plus t cells now we will learn all about these different receptors on the surfaces of these cells next semester when we look at the immune system in biology the cd4 receptor is a specific type of protein on the cell membrane of rt lymphocytes we also have these cd4 receptors on the surfaces of macrophages as well as dendritic cells both of those cells provide us with immune support as well now on the surface of the hiv molecule there are a number of different glycoproteins one of them known as glycoprotein 120 and glycoprotein 120 is responsible for binding to cd4 receptors on our t cells this facilitates the process of endocytosis which is going to allow for the genetic material of the virus to enter into our host t cells as a result of hiv affecting our own immune cells typically hiv infections lead to very low levels of properly functioning t cells and it's when that count of t cells drops below a certain level that an individual would be classified as having aids and as you can see once all of that genetic material has entered into the cell remember the viral rna has to go through the process of reverse transcription so it's the reverse transcriptase enzyme that creates the double-stranded dna molecule that double-stranded dna is ultimately going to be incorporated into our own t cells dna so then ultimately all of the genes within that viruses dna are going to be coding for brand new viral particles brand new rna brand new glycoproteins and so as a result we have these completed hiv particles that are then assembled and then are going to ultimately leave the cell now with our t cells the new hiv particles are simply going to destroy the t cell and so they're going to exit by breaking it open whereas within our macrophages which is a different type of phagocyte the macrophages live a lot longer and the macrophages are actually going to create these little hiv buds where we're going to have exocytosis of these hiv particles out from that macrophage and so because the human immunodeficiency virus is capable of impacting our t cells it uses our own machinery to be able to make new viruses and in the process destroys the t cells that it's infecting and so as a result we now have an individual who is going to be immunocompromised right and so now they are more susceptible for developing opportunistic infections and so the tissue infected now we know it's specifically the cd4 plus t cells hiv is an rna virus and ultimately causes immunodeficiency and typically death in individuals with hiv is caused by some sort of opportunistic infection now we're going to go through a number of other viruses as we finish off this lecture the common cold is caused by a variety of different viruses there's over 100 that can cause the common cold so really with the common cold there's no specific vaccine and with these viruses they tend to rapidly evolve so that there's no way really of producing a vaccine that's going to be able to target them um ultimately the signs and symptoms we get from the common cold are going to be those typical upper respiratory types of symptoms right congestion sneezing your sore throat a cough but what's happening here is you have the infection of the epithelial cells of that upper airway and so here with either rhinoviruses adenoviruses respiratory sensitile virus as well that can be included here are the coronaviruses covid19 is one specific type of coronavirus named because of its structure coronaviruses though as a whole typically cause these types of upper respiratory conditions now influenza is our flu virus and the influenza virus also impacts both the sinuses as well as the upper and now influenza typically infects the sinuses but also the upper airway now influenza is an rna virus and so as we mentioned rna viruses have a high mutation rate there are three types a b and c with a b being the most common and typical signs and symptoms kind of look a lot like the common cold with the addition of aches so muscle aches as well as a fever now one of the problems with the flu and with high flu death rates and this is why we have the vaccine that we do is in the immunocompromised or even elderly populations we tend to see opportunistic infections when the lungs are impacted and so as a result of there being some sort of congestion in your lungs you can end up with either bacterial or viral pneumonia developing as a result and that's typically the most common opportunistic infection that can occur with any type of originally upper respiratory infection now the herpes virus is capable of being passed on during its lytic cycle all right so the herpes virus is capable of being passed on skin to skin and so when an individual who has the herpes virus whether it presents as sores around the mouth known as cold sores or stores around the genitals it's when the epithelial cells have broken open and now the virus particles are then exiting from the body so when an individual's epithelial cells become infected by the herpes virus herpes virus then moves into the sensory neurons and then it spends that lysogenic also known as latent cycle inside the sensory neuron and then under periods of stress when the person is immunocompromised the virus then moves from its lysogenic cycle into its lytic cycle and this is when the cold sores form so this is typically why an individual who has had a herpes infection will experience cold sores whenever they're under periods of stress now with hpv human papilloma virus hpv is an sti there are over a hundred different strains and there are two specifically that have been linked with cervical cancer and this is one of the reasons why they perform a pap smear at an annual physical they're wanting to look at a typical cells that line the cervix to see if there are any pre-cancerous changes that may be occurring because remember you have a normal type of epithelial tissue in all regions of your body if a swab is taken or epithelial samples are taken and they can detect that there are changes occurring in the cell type in that region that is an indication of precancerous changes now as there are many different strains some of them can cause warts but others also cause no symptoms most infections resolve by the immune system on its own within one to two years and now with the most common strains that can cause cervical cancer they now have the immunization programs within schools to be able to protect against those specific strains with hepatitis this virus has very specific receptors that bind to receptors on the surfaces of the hepatocytes remember hepato referring to liver so these are the cells that make up our liver there's five different types of hepatitis a through e type a and e are passed on through contaminated foods so this is known as the fecal oral root so if an individual was to go to the washroom and not properly wash their hands and they had some remnant of fecal matter on their hands and then they went to make food the food is now contaminated and you ingest that food your risk of both type a as well as type e hepatitis now with type b c and d this form of hepatitis is passed on through body fluids but ultimately these three strains are the most common cause of both liver cirrhosis which is damage to the liver as well as liver cancer now anytime the liver is impacted the liver is responsible for being able to get rid of bilirubin and bilirubin contains a yellowish pigment and is formed by the breakdown of blood cells so every time a red blood cell dies every 120 days we need to excrete that bilirubin from the body and that processing is done by the liver when the liver's function is impacted we start to build up that bilirubin in our bodies and ultimately can become very jaundiced so any type of liver diseases or abnormalities and function you can end up with jaundice being one of the classic signs and symptoms other symptoms include extreme fatigue nausea vomiting as well as diarrhea they've developed the twin ricks vaccine which gives both vaccines for hepatitis a as well as hepatitis b and this is typically given to individuals who are going to be traveling to specific regions that have been deemed higher risk for contamination from hepatitis the rotavirus is a common one in children and usually all children get a rotavirus infection by the age of five now the main sign and symptom is very severe diarrhea and so you have to make sure that when you're losing all of that water that the child is going to be adequately rehydrated in order to make sure that they don't become dehydrated and so lastly here we have the epstein-barr virus which is responsible for causing mono which is the more common name for mononucleosis now with the epstein-barr virus it affects our b lymphocytes as well as the epithelial cells and is a very common type of herpes virus which is transmitted by saliva 90 of adults have acquired and have immunity by age 40 some individuals will have recurrent symptoms that extend beyond the initial acute symptoms so initially symptoms would be fever swollen lymph nodes rash or throat headaches and abdominal pains and those are more or less classic symptoms of any type of viral infection the one key element here is extreme chronic fatigue where individuals are unable to get out of bed and sometimes individuals can then have relapses where that infection uh impacts them later on in life as well okay and that brings us to the end of the lecture for this week as well as the end of the lectures for this course please let me know if you have any questions or concerns in the meantime otherwise i look forward to seeing you all in tutorial take care