In this video, we'll go through Salmonella and talk about everything you need to know in order to answer your microbiology questions correctly on USMLE and COMLEX. As a brief overview, Salmonella is a gram-negative rod. It's motile, it's acid labile, it's oxidase negative.

It's facultative intracellular, and it's non-lactose fermenting. People say Salmonella, but the word Salmonella really refers to a group of multiple subtypes of bacteria. And then there's typhoid types and non-typhoid

subtypes. Sometimes you'll see this written as NTS, which stands for non-typhoid Salmonella. And so if you are reading about Salmonella, learning about it, studying about it in class, what have you, you really want to understand that although we say Salmonella, that's an

umbrella term which refers to a collection of two subtypes. And for the purposes of USMLE or COMLEX, you can think about this and conceptualize this as typhoid and non-typhoid. Typhoid causes one type of disease, non-typhoid

causes another. And as I go through this video, I will help you separate the clinical features of typhoid versus non-typhoid. But they share so many overlapping features that Salmonella really is one group. This causes gastroenteritis and

colitis. Pathophysiology here, there's three things that you need to know. One, we have a Vi antigen. So the Vi antigen basically is a polysaccharide, and what this does is it prevents phagocytosis. And therefore, Salmonella is

not destroyed by immune cells so VI antigen prevents phagocytosis that's the big takeaway here then you have the presence of a flagella and the flagella one as all flagella do promotes motility but two it's responsible for the evolution of

something known as a Type 3 secretion system you don't really have to know the fine points of a of a Type 3 secretion system but in short this allows salmonella and other bacteria who also have a type 3 secretion system to attach

to and insert bacterial contents into non-phagocytic cells what's really important for the purposes of your board exams is that this does not this is not in shigella and that's a big differentiating feature because salmonella and shigella can present very

similarly and have a lot of overlapping features but one thing that is a big distinction between the two between salmonella and shigella is that shigella has no flagella no flagella in shigella it Rhymes so it's kind of easy to memorize lastly we

have an endotoxin and this endotoxin targets the neurovascular system and once the endotoxin gets inside of the host it decreases circulating neutrophils which of course limits the immune response and makes it more likely to cause overwhelming infection now in short the way that

salmonella gets in is through intestinal epithelium so it goes through the intestinal epithelial M cells and once it does that it enters the intestinal epithelium through the M cells ultimately it reaches lymphoid cells of the Peyer's patches so if you're if you're

having nightmares from your anatomy and physiology class here come some Peyer's patches once it's in the Peyer's patches it after crossing the intestinal epithelium it then gets disseminated throughout the reticuloendothelial system once it disseminates through the reticular

endothelial system it can cause serious overwhelming systemic infection so for the purposes of exams what's really high yield to take away from this video is that the infection goes through the M cells through the Peyer's patches hits the macrophages and then gets disseminated

through the reticuloendothelial system again this is all possible because of the toxin the Vi antigen and the flagella type 3 secretion system so you do need to know this you need to memorize these things for your exams because they do show up a lot so the first pneumonic

that I have for you is that VI prevents phagocytosis and you see VI in prevents or prevents phagocytosis so VI prevents vents big big big high yield point and then for the flagella you need to know that the flagella is what's responsible for that

type 3 secretion system so just change flagella to having uh three owls for type three secretion flagella type 3 secretion so prevents and flagella if you can remember those two things you know the pathophysiology of Salmonella let's move

on to clinical features so as I told you when this video started really there are two subtypes of Salmonella your there's your non-typhoidal Salmonella and your typhoidal Salmonella now your non-typhoidal Salmonella is what people classically

think about when they think about the generic term salmonella, that is to say, a food-borne gastroenteritis, plus or minus bloody diarrhea. This type of salmonella is associated with reptiles, amphibians, poultry, and eggs. So if on your exam you see any of these buzzwords, start to

think non-typhoidal salmonella. The answer is going to have salmonella in the name. I would be pretty surprised if the test writer gave you both subtypes, so if you see salmonella, chances are that's the correct answer. But again, know the buzzwords: reptiles, amphibians, 

poultry, and eggs. You're looking for symptoms of a food-borne gastroenteritis, plus or minus bloody diarrhea. And then we have typhoidal salmonella, and this is given the name typhoidal because it causes the disease known as typhoid

fever. So what you see here is early constipation, some non-specific GI symptoms, and then what's really key is rose-colored spots on the abdomen. That's a very specific finding, and chances are they will write rose-colored spots or they'll show you a picture of

rose-colored spots on the abdomen. Sometimes you see what's known as pea soup diarrhea, but that buzzword has kind of fallen out of favor. So no, the spectrum of illness: no constipation, pain, the rose-colored spots on the abdomen, and diarrhea. You don't

necessarily need to memorize the term "pea soup", but it may help you in typhoid fever. With this typhoidal salmonella subtype, you really want to be aware of the potential for septic shock, hepatosplenomegaly, or meningitis. So these

are complications of typhoid fever of that typhoidal subtype of salmonella and what's really high yield to know is that typhoidal salmonella is stored in the gallbladder of chronic carriers and this increases the risk for gallbladder

cancers so this is a really high yield point which shows up on exams a classic test question is that they describe somebody with salmonella and then at the end of the vignette they ask either where this is stored in a chronic carrier or what this increases

the risk for and you need to associate the clinical presentation or the pathophysiology of salmonella and then use that in a third or fourth order question to transition into one other associated high yield fact in this case having to do with the gallbladder last really high yield

clinical thing to know about salmonella is that in patients with sickle cell disease there is a marked increase risk of osteomyelitis and why this is is that in salmonella because of the clinical features of salmonella and the pathophysiology when you mix that with a

disease process where you have sickling an abnormal function in the capillaries and the liver and the spleen and the reticuloendothelial system you have an increased likelihood of osteomyelitis so we have decreased function of the liver and spleen so you

can see that in patients with sickle cell disease because of the sickling and potential to have problems in those organs but also salmonella causes hepatosplenomegaly and associated issues with the liver or spleen so this is just

a really confounding comorbidity also you have capillary occlusion of the GI system so because in sickle cell patients you get capillary occlusion due to the sickling salmonella enters as we said through the intestinal epithelium so when you get capillary occlusion of

the GI system it makes that GI system more at risk to have those infections which go through for example like salmonella that intestinal epithelium and then lastly because of the pathophysiology of salmonella as I talked about early on it's disseminated

through the reticuloendothelial system which limits the immune system's ability to fight off this infection so because of this you're having an increased risk of osteomyelitis so on your exam if you have a patient with salmonella another classic test question is to ask you

which of the following the patient is at increased risk for in sickle cell disease specifically so keep that in mind now for treatment non-typhoidal salmonella usually your treatment's going to be supportive on your exam if they want to

test you on treatment they'll give you typhoidal salmonella and the answer is going to be fluoroquinolones in somebody who cannot have fluoroquinolones or there's drug resistance you would then use ceftriaxone plus azithromycin but the

answer is going to be fluoroquinolones so that's all you need to know good luck

Salmonella

Dirty Medicine

Salmonella is a gram-negative, motile, acid-labile, oxidase-negative, facultative intracellular, and non-lactose fermenting rod.

Salmonella is an umbrella term for multiple subtypes, notably typhoid and non-typhoid (NTS).

Typhoid and non-typhoid Salmonella cause different diseases.

Salmonella causes gastroenteritis and colitis.

Flagella promotes motility and a Type 3 secretion system, allowing attachment to and insertion into non-phagocytic cells (unlike Shigella).

Endotoxin targets the neurovascular system, decreasing circulating neutrophils.

Salmonella enters through intestinal epithelium M cells, reaching Peyer's patches and disseminating through the reticuloendothelial system.

Mnemonics: VI prevents phagocytosis; flagella relates to the Type 3 secretion system.

Clinical Features: Non-Typhoidal vs. Typhoidal Salmonella

Non-typhoidal Salmonella: food-borne gastroenteritis, +/- bloody diarrhea; associated with reptiles, amphibians, poultry, and eggs.

Typhoidal Salmonella (Typhoid fever): early constipation, non-specific GI symptoms, rose-colored spots on the abdomen, and potentially pea soup diarrhea; complications include septic shock, hepatosplenomegaly, and meningitis.

Typhoidal Salmonella is stored in the gallbladder of chronic carriers, increasing gallbladder cancer risk.

Increased risk of osteomyelitis in sickle cell patients due to decreased liver and spleen function, capillary occlusion of the GI system, and dissemination through the reticuloendothelial system.

Non-typhoidal Salmonella: usually supportive treatment. Typhoidal Salmonella: fluoroquinolones (or ceftriaxone plus azithromycin if fluoroquinolones are contraindicated or resistance is present).