Cytolethal distending toxin, or CDT, is a bacterial toxin in Microbiology that damages host cell DNA, stops the cell cycle, and makes infected cells swell before dying.
Cytolethal distending toxin, usually called CDT, is a bacterial toxin that injures host cells by damaging their DNA. In Microbiology, you will usually see it discussed as a virulence factor in certain Gram-negative pathogens, especially some strains of Escherichia coli and Campylobacter jejuni.
CDT is named for the effect it causes. Cells exposed to it stop dividing normally, get stuck in the cell cycle, and then distend, which means they enlarge or swell. That swelling is not random puffiness, it is a sign that the cell has been damaged badly enough that it cannot finish replication and division the way it should.
The toxin has three parts: CdtA, CdtB, and CdtC. Of those subunits, CdtB does the damaging work. CdtB has DNase activity, which means it acts like an enzyme that cuts DNA. Once host DNA gets broken, especially as double-strand breaks, the cell activates damage responses that interrupt the cell cycle. If the damage is severe enough, the cell may die.
The other subunits help the toxin attach to and enter host cells. You can think of the three-part system as delivery plus damage. Without the binding and entry pieces, the DNase subunit would not reach the inside of the cell very well. That is why CDT is not just a random enzyme floating around, it is a coordinated toxin built to get inside host tissue and interfere with normal cell function.
In the gastrointestinal tract, that damage shows up as inflammation and disrupted epithelial cells, which can contribute to diarrhea, cramping, and other foodborne illness symptoms. This is why CDT comes up in the section on bacterial infections of the GI tract. The toxin is not the whole disease by itself, but it helps explain how certain foodborne bacteria make you sick after they colonize the gut.
A common way to study CDT in microbiology is to connect structure, mechanism, and symptoms. The structure is the A-B-like toxin system with three subunits, the mechanism is DNA breakage and cell cycle arrest, and the symptom pattern is damaged intestinal cells that cannot function normally.
Cytolethal distending toxin matters because it shows how bacteria can cause disease without simply invading and destroying tissue outright. In Microbiology, a lot of pathogenicity comes from toxins that change what host cells can do, and CDT is a clean example of that idea. It damages DNA, freezes cell division, and weakens epithelial barriers in the gut.
That makes CDT useful when you are comparing foodborne pathogens. Two bacteria can both cause diarrhea, but the mechanism may be different. Some toxins trigger fluid loss by altering signaling, while CDT damages the host cell cycle and can lead to cell death. Knowing that difference helps you match the symptom pattern to the organism or toxin.
CDT also connects anatomy and infection to molecular biology. You are not just memorizing a bacterial name. You are tracing how a toxin binds, enters, cuts DNA, and changes cell behavior. That chain of cause and effect is exactly the kind of reasoning microbiology labs, case studies, and exam questions tend to ask for.
It also shows why virulence factors matter in foodborne illness. A strain of E. coli or Campylobacter jejuni that makes CDT may cause more serious damage than a strain without it, even before you bring in host immunity or dose. So CDT is a useful marker for explaining why some gastrointestinal infections feel more intense, last longer, or cause more cell injury than you might expect from the microbe alone.
Keep studying MICROBIO Unit 24
Visual cheatsheet
view galleryEscherichia coli
Some strains of Escherichia coli produce CDT, so the toxin is part of how certain E. coli infections damage the gut. This connection matters because not every E. coli strain is pathogenic, and toxin production is one reason the harmful strains behave differently from harmless ones. When you see E. coli in a foodborne illness case, think about whether a virulence factor like CDT is involved.
Campylobacter jejuni
Campylobacter jejuni is another bacteria linked to CDT production and gastrointestinal disease. In microbiology questions, Campylobacter often appears in foodborne illness scenarios tied to undercooked poultry or contaminated food. CDT helps explain why the infection can cause tissue damage in the intestine instead of only short-lived stomach upset.
DNase
CdtB has DNase activity, so this term connects the toxin to a broader enzyme category that cuts DNA. That is the mechanistic clue behind CDT’s effect on host cells. If you know what DNase does, you can predict why the cell cycle stops and why DNA damage responses turn on after exposure to the toxin.
CAMP factor
CAMP factor is another bacterial virulence-related term that often appears near toxin discussions, but it works differently from CDT. CDT damages host DNA inside cells, while CAMP factor is associated with enhancing hemolysis in certain bacterial interactions. Comparing them helps you separate toxins that act on host DNA from toxins that act on membranes or red blood cells.
A quiz question may give you a foodborne illness scenario and ask which toxin causes DNA damage and cell cycle arrest. That is when you identify cytolethal distending toxin and connect it to CdtB’s DNase activity. In a short answer or case analysis, you might explain the chain from bacterial infection to host cell distension, epithelial injury, and diarrhea or cramping.
If you are looking at a lab image or concept map, you may need to pick out the toxin’s mechanism rather than just the organism name. A strong response ties the toxin to double-strand DNA breaks, growth arrest, and cell death. You may also need to distinguish CDT from toxins that mainly cause secretion or membrane damage, since the outcome in the gut is not the same.
CDT is a DNA-damaging toxin that arrests the cell cycle and can kill host cells, while cholera enterotoxin drives watery diarrhea by changing signaling and causing fluid secretion. They can both show up in gastrointestinal infection contexts, but they act very differently. If the question emphasizes DNA breaks, distension, or cell cycle arrest, that points to CDT, not cholera enterotoxin.
Cytolethal distending toxin is a bacterial toxin that damages host DNA and stops cells from dividing normally.
Its three subunits work together, but CdtB is the part with DNase activity and the main DNA-damaging effect.
CDT can make infected cells swell and eventually die, which is why the toxin is linked to gut injury and foodborne illness symptoms.
In Microbiology, CDT is a good example of a virulence factor that acts through cell cycle arrest instead of just direct membrane destruction.
When you see CDT in a case, connect it to pathogenic E. coli or Campylobacter jejuni and to gastrointestinal disease.
Cytolethal distending toxin, or CDT, is a bacterial toxin that damages host cell DNA and causes cell cycle arrest. In Microbiology, it is often discussed in connection with foodborne pathogens like some strains of E. coli and Campylobacter jejuni. The name comes from the way cells swell and stop dividing after exposure.
CDT enters host cells and its CdtB subunit acts like a DNase, cutting DNA and causing double-strand breaks. The cell responds by halting the cell cycle, and if the damage is severe, the cell can die. That is why the toxin leads to distension and tissue injury instead of normal cell growth.
No. CDT mainly damages DNA and disrupts the cell cycle, while some other bacterial toxins cause diarrhea by altering ion movement and pulling water into the intestine. CDT can still contribute to diarrhea and cramping, but the mechanism is cell injury, not just fluid loss.
It helps explain why certain gastrointestinal infections cause more than temporary stomach upset. If a pathogen makes CDT, it can injure intestinal cells, interfere with the gut lining, and contribute to symptoms like diarrhea and cramping. That makes the toxin a useful clue in case-based questions about bacterial GI disease.