Transcript of Staphylococci – Microbiology | Lecturio

[Music] hello and welcome to bacterial infections today we're going to talk about Staphylococcus and streptococcus and when you listen to this lecture you'll be able to know the structure and virulence factors produced by the staphylococci and the streptococcus I you'll be familiar with the pathogenesis and the epidemiology of diseases associated with Staphylococcus I and streptococcus I you'll know which drugs can be used to treat staphylococcal and streptococcal infections and you'll become acquainted with the available streptococcal vaccines let's dive into staphylococci first these are causative agents of abscesses and toxin mediated diseases here we have a photograph of Staphylococcus aureus these are grand positive cocci and they're often called grape like clusters so if they look like grapes to you purplish so that's the morphological appearance of Staphylococcus I staphylococci colonize the nose and other mucous membranes and the skin of 30 to 40 percent of humans 30 to 40 percent of people are carrying these bacteria as part of their normal flora not everyone all right but some of them do in your nose mucous membranes even on your skin these bacteria nevertheless under some situations can cause a variety of diseases they include focal abscesses and what we mean by that is an abscess in a very specific place like on the skin where it would be a boil many of you may have had boils before focal infections a very raised pus-filled lesion we'll see some of these in a moment and but these can also occur inside of you not just on your skin for example in your lungs bones other organs kidney and heart a general feature of the staphylococci is that they secrete potent exotoxins we talked about exotoxins in a previous lecture on bacteria these are proteins that are produced and elaborated from the bacteria that have effects on the host in the case of staphylococci these include the toxic shock syndrome toxin staphylococcal scalded skin syndrome and food poisoning these are all a consequence of the production of toxins the toxic shock the scalded skin the food poisoning are all consequences of toxin production and their effects so among the toxins that staphylococci produce are lipases and hydrolases these have as an effect to degrade the lipids of your skin and that in part contributes to the production of these boils these staphylococci can spread from person to person via aerosols respiratory spread produced by coughing or sneezing or even talking did you know that as I'm speaking now I'm actually making an aerosol and so if you are standing right in front of me you could be infected and it's in particular letters like pee pee where I'm sending out puffs of aerosol that's one way that people can spread I don't have to sneeze or talk or cough so person-to-person by respiratory aerosols or by direct contact these bacteria can be transmitted of course if you already have the staphylococci this is not relevant but as I said there are many people who don't have them and they can acquire them from others by these routes of transmission now as I said before they're on a certain percentage of humans on the skin and they remain they're harmlessly typically and they don't penetrate unless there's damage to the skin you have a cut that pushes the staph aureus deeper and it can then cause an infection or in a mucous membrane as well if you have a cut in the inside of your mouth it may introduce the bacteria into deeper tissues where it can then cause a problem so if they are left and they're normal places they're okay and problems arise when there are damages occurring so things like burns wounds of various sorts lacerations even an insect bite certainly surgery variety of skin diseases all these conditions can let staph aureus come in when you have surgery either one of the first things they do is to extensively wash the skin where you're going to be cut with a preparation to sterilize the area or reduce the number of bacteria if that's not done properly the staph aureus will be introduced into the wound and you can have serious infections of the sort that we're going to talk about so let's look at an abscess here's a photograph of a man you may think that this is in fact a nipple but it's not it's an abscess caused by a staphylococcal infection the nipple is a little bit south of this boil on his chest so this is an example of a boil caused by a staphylococcal infection many people have had these here the infection remains localized it is in this boil and it doesn't go beyond that this boil contains pus and that's called an abscess or a fir uncle interesting word for uncle is one boil like this a carbuncle is when you have several boils together makes a larger structure for uncle carbuncle so this is this is a typical boil we call them colloquially or an abscess when the bacteria spread beyond the initial boil in subcutaneous or sub mucosal tissues this is called cellulitis so the staphylococcal infection when it spreads beneath the skin cellulitis as you might predict one of the main immune defense cells important for regulating Staphylococcus replication and spread are neutrophils these maintain a balance of the bacteria in normal people and if your neutropenic that can be a problem in controlling staphylococcal infections very early an infection let's say you have a cut you and that introduces the staphylococci which you happen to have on your skin into deeper tissues there's a battle between the bacteria and your immune system involving neutrophils and other cells early in the infectious process many neutrophils are killed by the bacteria and these release lysosomal enzymes the neutrophils are full of them it's part of their armamentarium for killing bacteria when the neutrophil dies they're released into the tissue and those enzymes then damage your tissue and they contribute to the formation of a boil let's take a little bit of a deeper look at what this boil actually is or abscess and more precise terminology so here is a diagram of the abscess on this slide an abscess is walled off with a capsule made of fibrin this is a host reaction to the bacteria the host makes a fibrin capsule to try and restrict the bacteria to this one place now the consequence of this is that the bacteria are also isolated from the immune response so it's actually a consequence both of host and bacterial action within this boil or abscess we have dead neutrophils which are killed by the bacteria and this produces the pus we have epithelial cells we have bacteria and fluid and so this grows to a certain size is painful to a certain extent and that's what an abscess looks like staph aureus makes a number of what we call virulence factors these are toxins and other proteins that are made that help it to spread and overcome host defenses and there are a number of them in the center of that slide there are the staphylococci and you can see elaborating a variety of proteins like leukocidin x' he mollisons protein a coagulase --is and proteins that help make fibrin clots dissolve let's look at some of these in some detail let's take a look at some of the virulence factors produced by Staphylococcus I these are grand positive bacteria with a thick outer wall of peptidoglycan and surrounding that is a capsule which you may remember from our basic discussion of bacteria the capsule is important for inhibiting phagocytosis in this picture we have a macrophage trying to take up the Staphylococcus and the capsule will inhibit that reaction will resist its because of course once the bacteria is inside of the cell it could be destroyed the outer surface of the bacteria just below the capsule consists of peptidoglycan which you remain remember is alternating chains of carbohydrates cross-linked with short peptides this product of the Staphylococcus activates complement this is a host defense against infection and complement will have various inflammatory procedures it will cause lysis of the bacteria and production of cytokines and so this is part of the inflammatory reaction that goes on inside the carbuncle the bacteria also make a protein called protein a this is quite an interesting protein in the diagram you can see the protein a is on the surface of the bacterium it's shown in that little green box what this protein does is bind the FC portion of antibody molecules so that you know antibody molecules are Y shaped molecules the FC is down at the bottom and the antigen binding sites are at the top normally your antibodies would bind the Staphylococcus but the Staphylococcus is binding the antibody the other way so it can't bind the bacterium and this reduces the ability of the bacterium to be taken up into macrophages by opsonization very clever strategy for avoiding that process the cap sue the catalase is produced by Staphylococcus I this is an enzyme that Cleaves hydrogen peroxide that's hydrogen peroxide h2o2 shown right there peroxide is produced by cells like macrophages it's it's product is to destroy bacteria bacteria in turn make an enzyme called catalase and this will cleave the hydrogen peroxide to evade destruction very clever the bacteria also produced an enzyme called coagulase which converts fibrinogen to fibrin and that helps to make a clot that surrounds the boil and isolates the bacteria from the immune response staphylococci also make pore forming toxins like tea mollison's leukocidin x' and hyaluronidase --is that digests the extracellular matrix all of these in an effort for the bacteria to spread and avoid host defenses and we've talked about many of those before staphylococcal infections are very difficult to treat antibiotic resistance has become widespread among the staphylococcal strains that colonize us there are many beta lactam aces in these as we discussed in another lecture on general bacteria and those beta lactamase is encode resistance to the penicillin type antibiotics this what this resistance is widespread in addition the bacteria make a penicillin binding protein to a which further makes them resistant to penicillin class antibiotics and you may have heard the term mmrsa or MRSA to describe these bacteria this stands for methicillin-resistant Staph aureus and this is very popular in the press to talk about MRSA as a super bug because they're extremely difficult to treat almost impossible to treat with antibiotics so Marissa describes the most resistant of these strains of staph aureus so these are these are serious infections what kind of other diseases do these cause they cause staphylococcal scalded skin syndrome try and say that four times quickly this is a skin illness as you can see here and it I think the name tells you what it looked like this mainly affects neonates this is caused by sloughing of the skin the skin is coming off its red and angry looking caused by toxins produced by the Staphylococcus I specifically talks exfoliated toxins a and B exfoliation the loss of your skin you can also describe a disease called toxic shock syndrome TSS which became popular not very long ago this is accompanied by fever skin rash hypotension low blood pressure and also peeling of the skin exfoliation toxic shock syndrome was first described in connection with the use of highly absorbent tampons that allowed organisms to proliferate tampons went through a revolution in their production where they became extremely absorbent and also would block off the vaginal canal and the makers thought this was a great thing because it's convenient for women but it turned out that these trapped the staph bacteria in the vaginal canal allowed them to proliferate in and around the tampon and elaborate toxins and this brand new disease that had never been seen before toxic shock syndrome suddenly was described and that's a staphylococcal disease associated initially with the use of tampons but now we know there are other causes as well one of the main toxins produced by Staphylococcus eyes that causes toxic shock is called TSST one toxic shock syndrome toxin number one and this is an anthro toxin it actually acts as a super antigen super antigens bind the t-cell receptor and the major histocompatibility protein on the surface of cells and cause massive release of cytokines from macrophages and T cells that are then responsible for the symptoms se of toxic shock syndrome the whole idea of toxic shock elaborates from these cytotoxins that our Purdue staphylococci can also cause food poisoning we've been talking about skin diseases of various sorts but they can also be in your food and they produce enterotoxins that are in the food when you eat it these make you sick and the bacteria if they contaminate the food and you can imagine that someone may have staph aureus on their hands they're preparing food they haven't washed their hands they don't wear gloves you now have staph aureus in the food if it's not kept cold if it's at room temperature which sometimes happens during food production or serving the bacteria will grow they will produce their toxins and when you eat it you will get sick this typically happens with meats including poultry egg products salads milk and dairy products so if you ever have been to a buffet where there's lots of food spread out on the table if it sits there for hours at room temperature the bacteria can grow and make their toxins next time you go to such a function make sure the people are wearing gloves if they're not you should just stick with the wine and don't touch the food this disease when you ingest these toxins causes nausea vomiting stomach cramps and diarrhea and it's typically rather rapid onset so food poisoning where you are eating food that has a toxin in it already the onset is quick so if you eat something in an hour or two later you're vomiting you can say well that could be a staph aureus toxin caused food poisoning in contrast if it takes a few days to get sick that means the bacteria have to replicate in you before you get sick so this is a rapid onset food poisoning caused by Staphylococcus I and then in two or three days you recover [Music]