Streptococcus Pneumoniae

by Vincent Racaniello, PhD

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    00:00 why it's an autoimmune disease, rheumatic fever after infection with group A streptococci.

    00:01 Another important Streptococcus is Streptococcus pneumoniae, a specific species of streptococci, also known as the pneumococcus. This is a famous organism on so many levels. Here it is in this picture, it is usually cocci in pairs and this bacterium was famous in research and medicine. In research it's famous because it was used to show that DNA is the genetic material in the 1940s in a classic experiment. It's also famous because it's a very common causative agent of community acquired bacterial pneumonia, pneumococcal pneumonia. What do we mean by community acquired? You go out in the community and you get it from someone else as opposed to hospital acquired for example. So this is the most common cause of that kind of pneumonia. Over a million deaths every year throughout the world caused by Streptococcus pneumoniae, so this is a serious infection. There used to be many more, but we learned how to control it with antibiotics. Humans are the reservoir for this bacterium, some of us harbor them and others do not. If you happen to not have a pneumococcus in you and you are infected from someone else, you may be able to deal with the infection readily, you may clear it and never get sick, or you may develop pneumonia, lung disease and the outcome really depends on many factors including the genetic makeup of your immune system, whether you have any sort of disease that would predispose you to lung disease, such as another type of lung disease or if you're a smoker, this often is a predisposing factor.

    01:48 And finally we think that the strain of pneumococcus also makes a big difference, some are virulent and others are less so. This diplococcus or pneumococcus, is spread from person-to-person by respiratory droplets, very much like other streptococci, so again a carrier here maybe doesn't have disease, is speaking with someone who doesn't have the bacterium, who may be older and compromised in some way and that person can acquire the bacterium and develop pneumonia. So initially you inhale the bacteria, it colonizes your nasopharynx, the upper part of your respiratory tract and then it may replicate and spread down into the lungs and there cause pneumonia.

    02:31 Conditions that decrease your cough reflex are important for susceptibility to pneumonia.

    02:38 Coughing is an important way of expelling organisms in your mouth and nasopharynx. We also have something called a ciliary elevator in our respiratory tract. Our respiratory tract is lined with cilia, these are tiny hairs that constantly move and their function is to take any particles that you inhale and bring them back up again. So your tract is lined with these cilia and it is also covered with mucus and if you inhale a particle, one of your reactions maybe to cough and expel it, another thing that may happen if it's not very large, is the ciliated elevator may bring it up, goes into the back of your throat and then you swallow it and it gets digested in your stomach. You do this routinely, whenever you swallow, you're actually swallowing material that's come up from your respiratory tract. Some people spit instead, you know who they are, they are walking around the streets spitting, which is kind of a gross habit, better is just to swallow it and let it get digested. Anyway if you smoke, you inhibit that ciliary elevator, you slow it down and that's why smokers in particular have more predisposition to respiratory diseases such as this one.

    03:54 The pneumococcus carries out a classic struggle with phagocytes, the phagocytes want to eat it, of course the bacteria don't want to be eaten, they want to multiply and survive to infect another day, so we have a battle between these two. The bacteria have a thick capsule that makes them resistant to phagocytosis, this is a nice illustration. Capsule makes the bacteria bigger and it also has specific chemical interactions with the macrophage, the host on the other hand has a protein called C-reactive protein, CRP. This binds the teichoic acid in the outer membrane, the outer peptidoglycan layer of the bacteria. Remember teichoic acids are stuck into that peptidoglycan, if you don't remember, go back and listen to me talking about it on one of the earlier bacterial lectures. This binding of the protein to teichoic acid activates complement, which is a host defense system that can then lyse the bacteria.

    04:55 We can treat strep pneumoniae infections, in fact there was a time when they were uniformly lethal, but the development of penicillin shortly after World War I revolutionized the treatment of these infections and made people live who would otherwise die, but guess what? The overuse of penicillin and penicillin-like antibiotics has selected for resistant bacteria and so now if you get a pneumococcal infection, it is much harder to treat. Resistance involves penicillin binding proteins that prevent the antibiotics from working; these are beta-lactamase antibiotics. We now have vaccines that can be used to prevent infections and there are two I want to tell you about. One is a pneumococcal polysaccharide vaccine for adults. So if you are an adult and you were never immunized, you should get this so you don't develop pneumonia caused by this bacterium at an older age when your lung function starts to decrease. This vaccine will protect you against 23 different serotypes. There is also a vaccine for kids, you should give it to them, it's called the pneumococcal conjugate vaccine. It contains 13 different serotypes of pneumococcal antigens linked to protein carriers, so give it your kids and they won’t have to get the vaccine when they get older because they will be protected.

    06:22 So today we have talked about two kinds of gram-positive cocci that caused a variety of skin and systemic infections, the Staphylococcus and the Streptococcus, diagrammed here. And

    About the Lecture

    The lecture Streptococcus Pneumoniae by Vincent Racaniello, PhD is from the course Bacteria.

    Author of lecture Streptococcus Pneumoniae

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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