 Welcome back to our meds smarter lecture series where we're taking a smarter approach to preparing future physician Before we get started if you'll take just a quick minute and click that like button and also Subscribe and turn the bell on so that you'll be notified when we post new videos Let's continue on in our discussion of gram negative bacteria and today We're going to do a little bit of a comparing contrast between Salmonella and Shigella. They are both very commonly Confused so we're going to discuss some various things that are different between the two To help you get those questions answers are right on the test So first and foremost both of these Salmonella and Shigella are going to be gram negative rods Okay, we've already established that we're talking about gram negative bacteria. They're also both non lactose fermenters they are both oxidase negative and Then they can invade the GI tract with the m cells of pyropatches So if you see back gram negative rods in pyre's patches, it's probably going to be Salmonella or Shigella You got to remember that it could be either of those so we need to investigate them further with further Information from that question to be able to determine which particular one we're dealing with and then even beyond that What particular treatment that we need to use? So let's look at a chart here that's going to give us some information to compare and contrast Salmonella and Shigella We're specifically going to talk about two different types of Salmonella We have Salmonella typhi and then just all the other Salmonella species Except typhi as you can see in that second column and then Shigella will be on the third column here So what are the reservoirs for these? various bacteria Well first and foremost what is a reservoir remember the reservoir is the habitat which these normally live and grow and multiply So with Salmonella typhi these only grow in humans So it's not going to grow elsewhere and then come into humans You know think of ticks and that kind of stuff and how those can disseminate elsewhere With Salmonella that is not typhi not only can it be in humans, but it can also be in animals So that's an important aspect there and then Shigella is in humans only as well So the difference between these three is that the other Salmonella species besides typhi can Have a animal reservoir How do these spread? Well Hematogenously is going to be The way that Salmonella all Salmonella species are spread whether it's typhi or all the others they can all spread Hematogenously Shigella however does not spread through the blood. It's only going cell to cell Do any of these produce hydrogen sulfide? Well all of the Salmonella species do but Shigella does not So that's going to just differentiate between those two Salmonella all have flagella on them that helps them to do a salmon type swim Where it beats back and forth where it can move along in the blood there So both the Salmonella species have that Shigella does not which is why it has that cell to cell spread It cannot move on its own What causes the virulence with these particular bacteria with Salmonella typhi? It's an endotoxin as well as a vi capsule This is important for something that we'll talk about in just a little bit So keep that in mind that the Salmonella typhi does have a vi capsule The Salmonella all the rest of the Salmonella species only have that endotoxin. They do not have that vi capsule and Then Shigella has the endotoxin as well as the Shigatoxin, which is an entrotoxin So what is the infectious dose required for these particular bacteria to become infectious? So this is known as the ID 50 If you can remember back, what does the ID 50 mean that is going to be the value or the dose of bacteria specifically in this case where these Particular infectious agents are required to cause an infection in 50% of the test subjects So how high of a dose do 50% of the patients have to have to cause infection? Okay, so with a Salmonella typhi they have a high large inoculum required So they have to have a lot of this bacteria present to cause an infection in About 50% of the patients Why is that? Well, it is acid-lay bile meaning that it's inactivated by gastric acids So if this is consumed then the stomach acids can actually cause a decrease in the potential Transmission and infection of Salmonella typhi. This is also the same story for all the rest of the Salmonella species This is different. However for Shigella Shigella is acid stable meaning as it goes through that digestive tract It's very resistant to the highly acidic environment of the GI tract Therefore, it only takes a low amount of this particular bacteria to cause an infectious disease So if we treat these with antibiotics what happens to the excretion of them with all of the Salmonella species Giving antibiotics will prolong the duration of fecal excretion whereas with Shigella It's going to shorten that duration Couple more things to discuss here between these three different types of bacteria the immune response for Salmonella typhi is mostly going to be monocytes Whereas the rest of the Salmonella species and Shigella Polymorphic neutrophils are going to be part of the immune response for those particular infections How do these? Manifest themselves especially in the GI form with Salmonella typhi they get constipation followed by diarrhea With all the rest of the Salmonella species we have diarrhea by itself It could be a bloody diarrhea and then Shigella causes a crampy abdominal pain where you get that Tennismus or that muscle spasm, and it can also cause a bloody mucoid stool so if you remember back to just a minute ago, we talked about the Virulence factor and how Salmonella typhi has the vi capsule. That's important for this next point the vaccine Can these have a vaccine to decrease the risk of infection the answer to that is yes If they have that vi capsule so we can do an oral vaccine that will have the live attenuated version of Salmonella typhi Against that vi capsule or polysaccharide without that vi capsule or polysaccharide There's no ability for us to create a vaccine against the other Salmonella species or Shigella Therefore they have no vaccines for those cases All right, and what a couple of the things what are some unique properties about these specific ones so Salmonella typhi has a Particular disease named after it and that is typhoid fever to treat typhoid fever We're gonna use seph triaxone or a fluoroquinolone This can actually colonize the gallbladder in patients that are carriers So we talked about this only has a human reservoir So it can colonize the gallbladder and then potentially excrete out of the body and the feces That could then potentially infect other people through some contaminated surfaces the other Salmonella species outside of Salmonella typhi are Found most commonly in poultry eggs pets and turtles remember we said that this can be found in animals So the other Salmonella infections found in animals like poultry eggs pets and turtles We don't indicate any indication for antibiotic use to treat Salmonella Outside of Salmonella typhi. These are usually self-limited and they will resolve upon their own Most of the time within 24 to 48 hours If we do have a patient that has gastroenteritis That's often going to be one of those Salmonella non typhoid type Bacteria furthermore Shigella follows the four F's Finger flies food and feces. It's the most common causes of transmission for Shigella It is important to note that the invasion of the M cells with Shigella is what is key to its Overall pathogenicity that actually allows it to have a very little dose of toxin to cause the disease If you found this material helpful for your studying Please like and consider subscribing to the channel also share this video so that more people can benefit from it like you have