The next pathogen that we'll talk about is Corynebacterium diphtheriae. This is the bacteria that causes diphtheria. Diphtheria is a gram-positive, club-shaped bacillus. You'll be able to pick this up by looking at the slide

because it has metachromatic granules and the bacteria is arranged in what's called Palisades. That's just a fancy way of saying that it's V or L-shaped, and I'll show you an image on the next slide. Diphtheria is transmitted via

respiratory droplets. Diphtheria is basically pharyngitis, but it, you know, for lack of a better term, it's just upper respiratory tract infections. So those are the symptoms you want to look out for. There are some associated systemic symptoms, and we'll talk about

those as well. Historically, diphtheria is associated with either not being immunized against it or traveling to a region where there are low vaccination rates, and therefore the bacteria is more likely to exist, and you're more likely to contract it. Here's that image of diphtheria. So again,

metachromatic granules and Palisade formations. If you look on the top left of this slide, you see a really nice example of that V-shaped Palisade. So because this is a little bit more unique looking, I might know what this looks

like as compared to other bacteria where you don't really need to know what it looks like at all. As far as virulence factors goes, there's an exotoxin. It's a beta-prophage exotoxin. The buzz phrase that shows up all the time is ADP ribosylation of

elongation Factor two, so basically this exotoxin does that and that inhibits protein synthesis. And when you inhibit protein synthesis, certain tissues and cells can't grow, so we've got cell death. Now the way that I memorize this is I look at the word

diphtheria, which ends in AE, and I use that AE to remind me ADP ribosylation and E for elongation Factor two. So pretty straightforward really. The highest yield part of diphtheria is the clinical features because this is very unique. The

pseudomembranous pharyngitis is what you're going to see on your exam. So what this is is a grayish pseudo-membrane that will occur in the pharynx and you're going to see a characteristic picture like you see on this slide, and

that's telling you that the answer is diphtheria. So how the vignette will probably go is that you've got a patient who either is not immunized or who travels to an area that's endemic with a low vaccine rate. They start to develop

non-specific upper respiratory tract infection symptoms, so they might get erythematous pharyngitis to start, and then that red area of their pharynx will slowly transform into what you see here, that grayish pseudomembrane. The interesting thing about the

pseudo-membrane and what you might see in the vignette is that if you scrape it, it tends to bleed and it's made up of white cells, red cells, all these dead cells, different debris, and so if you scrape it, it bleeds, and so it's not the

same appearance it doesn't have the same characteristics of other types of pharyngitis, pharyngitises. So again you just want to know it starts erythematous, it turns to pseudomembranous in grayish and when you

see that transformation, the vignette is screaming at you that the answer is diphtheria. You know there's there are some systemic symptoms that can be associated with diphtheria so I want to point them out so that if you're doing a

question and you think you're like oh it's a pseudomembranous pharyngitis, this has to be diphtheria, but you see some of these other curveballs, you're not second guessing yourself. So some of those Associated symptoms include

cervical lymphadenopathy, myocarditis, acute tubular necrosis, and adrenal insufficiency. And because this spans over, you know, various organ systems, heart, kidney, adrenal, the laboratory abnormalities they can give you in the question might make you second-guess yourself, but don't second guess yourself

if you see a grayish pseudomembranous pharyngitis, the answer is 100% diphtheria. The reason that you have these Associated systemic symptoms is once that beta prophase exotoxin gets into the blood, gets into the lymphatics and

then disseminates throughout the body, it can affect the heart and cause myocarditis, the kidney and cause ATN, the adrenal and cause adrenal insufficiency. So just because you're seeing other Associated problems, don't second guess yourself. So that's pseudo-membranous

pharyngitis that's the main highest yield clinical feature of diphtheria and what you really want to know for your exam just for completeness sake though let's talk about cutaneous diphtheria so this is another type of diphtheria the

bacteria can manifest as a skin infection as well and there's a little bit of a difference here so how this works is the bacteria will directly touch a pre-existing skin injury so the patient in the vignette is going to have a skin lesion before the exposure to

diphtheria and then the diphtheria will directly enter that pre-existing wound and then once that happens you get some really nasty looking ulceration the interesting thing here is that just like in the pseudomembranous pharyngitis in

the throat you can have a grayish scaliness over these ulcers so the picture you see on my slide here doesn't really look gray but if you get the skin injury and you get cutaneous diphtheria you can see an ulcer with a little bit of grayish

scaliness over it so you can see gray in the throat on that pseudo membrane and you can also see gray on the pre-existing skin injury that turns into cutaneous diphtheria really briefly for for treatment you give an antitoxin plus either penicillin

G or erythromycin but the antitoxin is the most important thing so that's treatment here's the summary slide diphtheria is a club-shaped bacillus it's gram-positive it has metachromatic granules it's arranged in Palisades which is to say

that it can be in V or L-shaped formations. A major virulence factor is an exotoxin, remember ADP ribosylation of elongation Factor 2, and note for clinical features pseudomembranous pharyngitis with that grayish pseudomembrane in the throat.

plus or minus some systemic symptoms, and then less frequently and less high yield, no cutaneous diphtheria where a pre-existing skin injury becomes inoculated and turns into an ulcer. Treatment, antitoxin plus either penicillin G or erythromycin, that's all.

Corynebacterium Diptheriae

Corynebacterium Diptheriae

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