Vibrio cholerae is a bacterium in the genus Vibriones. The pathogen can cause the infectious disease cholera.
What is Vibrio cholerae?
Vibrions are gram-negative bacteria. This means that they can be stained red in the Gram stain. Unlike Gram-positive bacteria, Gram-negative bacteria have no cell wall other than the thin single-layered envelope of murein. Vibrions appear as curved rods. They live facultatively anaerobic, meaning that they can survive both with and without oxygen. Two species of vibrios are human pathogens. In addition to the bacterium Vibrio parahaemolyticus, these include the pathogen Vibrio cholerae. The species Vibrio cholerae includes several strains of bacteria. Not all of these bacterial strains are human pathogenic. Vibrio cholerae acquires its pathogenicity only through so-called bacteriophages that penetrate the bacteria. Bacteriophages are different types of viruses that use bacteria as host cells. Vibrio cholerae, like the other members of the Vibrio genus, can move with the help of a single flagellum. The flagellum is located at the end of the bacterial cell.
Occurrence, distribution, and characteristics
The bacterium Vibrio cholerae belongs to the aquatic bacteria. These live in water. Thereby, the bacterium is found in seawater as well as in freshwater. Brackish and coastal waters in particular can be contaminated with Vibrio cholerae. Areas of distribution are India and Central Africa. Contaminated water is also the main transmission route for cholera. In particular, untreated or inadequately treated drinking water is an important source of infection. But the pathogen can be transmitted not only by drinking the water. Food that has come into contact with the water can also transmit the bacterium. In endemic areas, freshly washed fruit is often contaminated with cholera pathogens. Plant foods often come into contact with Vibrio cholerae while still in the field. Fecal matter applied as fertilizer is often contaminated with Vibriones and acts as a transmission medium. However, infections occur much more frequently through consumption of food from the sea. For example, shellfish and other seafood in endemic areas are often contaminated with cholera bacteria. People who are ill with cholera excrete the pathogen in their stool. The pathogen can also be detected in vomit or in the juice of the small intestine. Even several weeks after symptoms have subsided, pathogens are often still found in the stool. Permanent excretion, however, is rare in Vibrio cholerae.
Diseases and symptoms
Vibrio cholerae is the causative agent of cholera. The bacteria release an exotoxin. Because this toxin exerts its effects mainly in the gastrointestinal tract, it is also called an enterotoxin. The cholera toxin inhibits the GTPase activity of a specific protein, so that at the end of a reaction chain there is ultimately an excess of cAMP. CAMP, the cyclic adenosine monophosphate, is a so-called second messenger, which serves the signal transduction within the cell. Due to the excess of cAMP, certain membrane channels within the intestinal wall become more active. On the one hand, this leads to increased chloride channels being incorporated into the membrane of the cells. In addition, there is also a loss of sodium. The connections between the epithelial cells of the intestinal wall become more permeable, resulting in a loss of electrolytes and water. This results in severe diarrhea, which can be accompanied by water losses of up to one liter per hour. Along with the water, many potassium and hydrogen carbonate ions are lost. Although cholera toxin causes the typical symptoms of cholera, cholera breaks out in only about 15 percent of all cases after infection with the pathogen. The incubation period is two to three days. After that, cholera characteristically progresses in three stages. The first stage begins with vomiting diarrhea. The stool is very thin and interspersed with mucus flakes from the intestinal mucosa. This gives the diarrhea a rice-water-like appearance. Only rarely is the diarrhea accompanied by pain or cramps in the stomach and intestinal area. The second stage is characterized by severe fluid deficiency due to fluid loss from the diarrhea. This stage is also called the exsiccosis stage. The patients’ hypothermia is conspicuous.In addition, a striking expression of the face develops with sunken cheeks and a pointed nose. Skin folds that are lifted with the fingers remain due to the exsiccosis. Hoarseness may develop as a result of fluid loss. The resulting hoarse voice is called vox cholera in medical terminology. The wrinkled hands, on the other hand, are known as washerwoman’s hands. In the third stage, general body reactions occur. Patients are dazed and confused. They develop a skin rash. In addition, complications such as pneumonia or inflammation of the parotid gland may occur. If the pathogens spread in the blood, blood poisoning (sepsis) can develop, often leading to coma or death. An initial tentative diagnosis can usually be made on the basis of the typical clinical symptoms. If cholera is suspected, the physician will prepare a stool culture and microscope the stool. However, a definitive diagnosis can only be made in the laboratory with the aid of an antiserum. Antibiotic therapy is only given in severe cases of cholera. The most important therapeutic measure is the intake of sugar, salts and fluids. To bypass the inflamed gastrointestinal tract, the doctor administers the substances intravenously. The World Health Organization additionally recommends oral administration of salt and sugar solution in water. With hydration and the use of antibiotics, the mortality rate of cholera has been significantly reduced.
