Clostridium

00:01 Clostridium a bacteria.

00:03 The Clostridium are gram-positive rods as you see on the slide here that are obligate anaerobes.

00:10 And importantly, they create endospores in the soil.

00:15 And on the slide, one can see those said needles looking very unusual, not a typical gram-positive rod.

00:22 Also under the microscope, one can see that these organisms are motile; they in effect swim about.

00:29 There are at least 50 and perhaps even more than 50 known species of the Clostridia.

00:36 But we're going to talk about four of them which are known to cause significant human disease.

00:41 The first of those is Clostridium perfringens, followed by Clostridioides difficile commonly known as C. diff.

00:50 Clostridium tetani the cause of tetanus and Clostridium botulinum the cause of botulism and also frequently used by those in the plastic surgery industry to create Botox.

01:06 Each of these organisms has a somewhat different mechanism of pathogenesis and we're going to describe each one.

01:12 The first, for Clostridium perfringens.

01:14 Typically, there are at least several subtypes; A through E based on the toxins produced by Clostridium perfringens.

01:23 Subtype A is the most virulent and therefore the one about which we know the most.

01:29 All of the types however produce an alpha toxin.

01:33 Now an alpha toxin is a very common type of toxin that is responsible for entering retrograde into its target cell and disrupting protein synthesis.

01:44 Typically when that happens, the affected cell loses the ability to sustain life and it dies by apoptosis.

01:53 In this case; Clostridium perfringens produced in the alpha toxin creates a lysis of the blood and the endothelial cells; those small cells which lie in the surface of the blood vessels.

02:06 This of course creates downstream effects of increasing vascular permeability along with hemolysis and tissue destruction a very nasty sequence of events which as you'll see creates very nasty disease associated with the organism.

02:22 In addition, many of the subtypes of Clostridium perfringens can produce an enterotoxin; entero for gut, of course makes sense it would cause watery diarrhea.

02:33 The way it does that however is by disrupting ion transport in the ilium which affects the absorption of water.

02:41 So in a way, enterotoxin's create a malabsorptive diarrhea; watery diarrhea.

02:48 Other toxins such as the beta and the Iota-toxin will also cause necrotizing activity, but these occurs somewhat less commonly. C. diff. Everyone knows about C. diff.

03:01 As of 2016, Clostridium difficile was reclassified and is now known as Clostridioides difficile.

03:09 How does C. diff. cause disease? Well, it's not just immunocompromised patients and unfortunately, it's no longer just patients who have been taking antibiotics.

03:18 A form of C. diff. now exists which causes C. diff. associated colitis or disease in otherwise healthy patients who may not have been exposed to lots of antibiotics.

03:30 How it causes disease however, is through another two toxins.

03:35 Enterotoxin or toxin A, again, as the name would suggest, this targets the intestines and it increases intestinal hemorrhage at the level of those enterocytes and thus, creates a secretory diarrhea, fluid secretion, so the diarrhea can be very much likely we'll eventually talk about in cholera.

03:54 The second toxin, toxin B, is a cytotoxin, a cell toxin, and this creates mucosal membrane destruction.

04:03 So, not only is it a secretory diarrhea, but there is blood and other cellular contents associated.

04:10 In addition, C. diff. has an adhesion factor so that it can bind very successfully to the colon cells and C. diff. creates spores that are highly resistant to any cleaning agents, specifically those ones used in hospitals.

04:27 And so, you'll see in a patient who has C. diff. colitis, very prominent warning sign saying that only soap and water hand cleaning will be effective.

04:37 The alcohol-based hand cleaners noted for all other types of infections don't work to eliminate the spores associated with C. diff.

04:47 Clostridium tetani, tetanus. This is a very interesting pathogenesis and we'll start with what happens normally at the synaptic junction in a central nervous system motor neuron.

05:01 Normally, one has the presence of excitatory transmitters which are released across the junction and bind in the following neuron but in a controlled fashion with a back suppressive inhibition mechanism via inhibitory transmission.

05:17 This would normally prevent continuous excitatory stimulation of that particular junction.

05:24 However, if we introduce Clostridium titani and its produced tetanospasmin, its toxin, this toxin has the ability to go into the junction where it can inhibit the release of the inhibitory transmitters.

05:40 It blocks the transmission of those.

05:42 Well, as you can imagine, this has a downstream effect of blocking the inhibition of the excitatory transmission so that particular junction is always on, it's always firing.

05:54 And that means that downstream, the motor cell which is stimulated by that is always turned on, it's always clenched.

06:02 So, as we see, the mechanism of Clostridium tetani is to block the inhibition, block the suppression of excitation which then allows for the motor itself to the motor muscle to be continuously turned on.

06:19 In an opposite fashion, the mechanism of Clostridium botulinum causes a paralysis, a hypocontraction of the muscle fiber. Again, let's start with how things look normally.

06:31 Here, we see the end junction of a motor neuron and how it interacts with the muscle fiber.

06:38 We see acetylcholine-containing vesicles which normally would be released through the junction to trigger contraction of the muscle fiber.

06:47 However, if we introduce Clostridium botulinum and its toxins which are a two-part toxin, those bind to the neuron motor end plate, allow insertion of the second toxin component, which then prevents release of the choline-containing vesicles.

07:05 That means that no acetylcholine-containing vesicles can go to the junction nor can they cross the junction and stimulate the muscle, and the muscle itself is not stimulated.

07:17 Therefore, we have an ultimate flaccid paralysis.

07:21 No ability to contract or stimulate the muscle to contract.

07:26 So, let's now look then at all four Clostridium species.

07:33 This is a way to compare and contrast the diseases associated with each.

07:37 First of all, habitat. All four Clostridium species we're talking about are associated with spores and the spores all can be found in the soil and related things.

07:50 So, for Clostridium botulinum, in the soil or in canned food.

07:54 In Clostridium difficile, the soil and unfortunately, intestinal flora.

08:00 Importantly, human beings are colonized with Clostridium difficile at least a certain percentage at a time normally.

08:08 Children up to aged two may be colonized 50% of the time.

08:13 Adults, who are otherwise healthy, may be colonized 10% of the time.

08:18 And everybody in between, those with chronic medical illnesses, those on chronic antibiotics, may be colonized with C. difficile and those toxins up to 30-40% of the time.

08:31 So, it's a very common presence of the organism but fortunately, not everyone gets disease.

08:37 Clostridium perfringens, the spores will also live in the soil but they also normally persist in the GI tract where they don't cause disease until we disrupt the bowel barriers.

08:50 And then Clostridium tetani, again, soil, water, in the sewer systems, and animal's normal flora.

08:58 Commonly, we think of tetanus as coming from a rusted nail or a rusted barbed fence, barbed wire fence, but in fact, it's not just the rusting itself as an anaerobic environment, but the presence of some sort of fecal contaminant on those implements which then can introduce tetanus.

09:16 How do the organisms look? Again, Clostridium is an anaerobic rod but it can look somewhat differently under the microscope as you could see in the slide there.

09:28 Specifically, Clostridium perfringens can be very large, almost box car-shaped rods and it does not have the flagella which might be seen in the other Clostridial species.

09:39 Clostridium tetani, small and racquet-shaped and it can be seen with a terminal spore.

09:45 The toxins, again, as we've already talked, the toxins are the major mechanism of injury or mechanism of disease for these species.

09:55 Claustridium botulinum has botulinum toxin which is abbreviated, again, in the plastic surgery world as botox and it is a two-part toxin.

10:04 Clostridium difficile has two toxins: enterotoxin A and cytotoxin B, each of which, again, has different specific effects but in combination, create the very secretory, very bloody diarrhea we associate with C. diff.

10:20 Clostridium perfringens has all sorts of toxins but the alpha toxin is the principle mechanism of disease causing cell death and causing that breakdown of the blood vessels in necrosis.

10:34 And then Clostridium tetani has tetanospasmin which, again, interferes in that junction as we talked about just previously.

10:42 Transmission. Clostridium botulinum, the spores classically exist in honey or in canned foods.

10:50 Sometimes, they're associated with picnics where the foods were poorly prepared.

10:55 As we'll talk about in just a bit, there's a form of neonatal botulism associated with ingesting the spores, pre-formed spores, in honey fed too early to an infant.

11:06 Clostridium difficile, the spores can exist anywhere and everywhere.

11:11 Again, they are common contaminants and common colonizers of the human GI system.

11:16 So, intestinal flora, which I'm sorry to tell you, lives everywhere can exist everywhere as well.

11:24 Recently, it was also noted that C. difficile spores in the organism themselves can aerosolize, can go into the air of the hospital room of an infected patient.

11:36 So, if you are a wise person and caring for a patient with active C. diff. colitis, you may wish to avoid this storm of C. diff. spores by wearing a mask.

11:46 Clostridium perfringens, the spores exist and are transmitted via contaminated food and also through entry from the gut itself, the GI tract as you see there.

11:57 And then Clostridium tetani, contamination of a wound or a cut.

12:01 Some breakdown in the skin barrier is first import or a penetrating injury such as with barbed wire or with the nail that coded with the spores in the organism from a fecal source.