Vibrio cholerae

Vibrio cholerae is a gram-negative, curved rod-shaped bacterium (genus Vibrio) that causes cholera in humans. Together with another species of the genus Vibrio belongs to the gamma subdivision of the Proteobacteria. There are two main strains of V. cholerae, classical and El Tor, and numerous serogroups.

History

For centuries, the disease remained unknown in Europe, spreading mainly in Asia and Africa. The first mention of this disease in Europe was made in 1503 by a Portuguese officer returning from India, recounting that a disease had caused 20,000 deaths. It appeared later in Europe and was the subject of a multitude of interpretations and theories by doctors. It was during the 1854 epidemic in London that the understanding of the disease underwent a great advance, when it was appreciated that the disease occurred near some wells, which suggested the contamination of the water. But this hypothesis was not immediately accepted at the time it harms humans.

Vibrio cholerae was found to be responsible for cholera by the Italian anatomist Filippo Pacini in 1854. from other diseases of unknown origin) to poor air quality. In the same year, Joaquim Balcells i Pascual described Vibrio cholerae. Thirty years later, in 1884, Robert Koch, who did not know Pacini's results, published the results of his work and the means to combat Vibrio cholerae .

In 1965, the bacterium was renamed Vibrio cholerae (Pacini, 1854) in homage to Filippo Pacini.

Epidemiology

Cholera is endemic in regions of the world with poor water, sanitation and hygiene infrastructure, such as sub-Saharan Africa and the Middle East regions. In developed countries, it is seen sporadically. It is currently endemic in 69 countries, including Asia, Africa and the Americas, with 1.3 billion people at risk, with sub-Saharan Africa being the worst. V. cholerae originated on the Indian subcontinent and caused six pandemics between 1827 and 1923. The seventh pandemic has been ongoing since 1961, reaching South America and most of the Western Hemisphere in 1991. Although widely underestimated, the World Health Organization estimates a total of 2.8 million cases with 91,000 deaths per year. Recently, cholera has continued to affect vulnerable communities such as post-earthquake Haiti (2010), Iraq, and Yemen, where natural disasters, refugee movement, war, and conflict increase the risk of infection and outbreaks. Although safe drinking water and advanced sanitation systems have made cholera a limited and treatable disease in Europe and North America, new strains of V. cholerae, ease of travel, and the constant migration of potentially infected people have posed serious public health concerns.

Features

Cholera bacteria.

Vibrio is a genus of gram-negative bacteria, belonging to the order Vibrionales, gamma-proteobacteria, shaped like curved bacilli. Biochemically, they are characterized by being positive in catalase and oxidase tests, they are also negative in adenine dihydrolase, and positive in ornithine decarboxylase. Vibrio cholerae specifically is sucrose and mannitol positive and nitrate reductase positive. It is a facultative anaerobic bacterium, and its metabolism is fermentative; they can ferment, among other substrates, glucose. They have polar flagellation, which gives them maximum mobility.

Although they are not very demanding nutritionally, specific media are used to isolate them from clinical samples. Sodium stimulates its growth and also tolerates alkaline pH, which is why alkaline peptone water is used for its cultivation. In the presence of V. cholereae there is an absence of polymorphonuclear cells.

In the case of the innocuous bacterial strain of Vibrio cholerae, the product of lysogenic conversion by the action of a bacteriophage, it also becomes a tremendously virulent strain that can cause cholera.

Isolation

From vomit or diarrheal feces, an aliquot is extracted and introduced into a transport medium. Of this, observation can be made fresh, under a phase contrast microscope, or through a Gram stain. There are antibody kits to carry out their determination and identification by immunofluorescence.

Once the suspicion has been addressed to the group, an aliquot is seeded in an enrichment medium that is selective, such as TCBS (containing thiosulfate, citrate, bile salts, and sucrose).

Once obtained in pure culture, the sample is processed by various biochemical tests: oxidase, LDC, ODC, among others.

There are agglutination procedures to determine the biotype; for example, O1 (called El Tor) and O139 are the most clinically relevant.

Grow rapidly on peptone agar, blood agar with pH close to 9.0; or on TCBS agar, and in 18 hours typical colonies can be observed. A few drops of feces can be incubated, for enrichment, for 6 to 8 hours in taurocholate-peptone broth (pH 8 to 9).

Virulence factors

• As adhesins, they have TCP pili, correlated with toxin.
• Somatic antigen O, a pyrogen of lipopolisaccharide.
• Antigen H of the scourge; protein antigen that allows the establishment of the bacteria in the mucosa of the small intestine.
• Hemolysins, in the biotype El Tor.
• Neuraminidase.
• Exotoxine, choleric toxin, main virulence factor.
• Zot Toxin: Increases the permeability of the intestinal mucosa affecting the structure of the intercellular unions of zonula ocludens type.
• Toxine Ace: Increases the potential difference on both sides of the membrane.

The transcription of TCPs and cholera toxin is regulated by the regulatory protein ToxT, which activates the virulence cascade.

Cholera Toxin

It is type AB . Its genes are clustered in the Ctx AB operon, coregulated with the aforementioned TCP pili.

• CtxA code for subunit A, activates biologically.
• CtxB encodes for subunit B, of binding the GM1 ganglion of epithelial cells.

There is a translational regulation that favors the greater expression of the B subunit; It consists of the possession by its mRNA of a ribosome binding sequence that is stronger than that of A.

An AB5 hexamer interacts with the ganglioside facilitating the penetration of the A subunit (actually the A1 fragment) of the toxin into the cytoplasm of the enterocyte. This fact allows the activation of cellular adenylate cyclase by ADP-ribosylation of the stimulatory G protein that regulates said adenylyl cyclase activity. This causes an increase in intracellular cAMP levels, opening the Cl^- channels of the apical membrane and keeping them open. Cl^- secretion is accompanied by Na⁺ secretion and since these are osmotically active molecules they will favor the secretion of water into the intestinal lumen. The volume of fluid secreted into the intestinal lumen exceeds the absorption mechanisms of the small intestine and colon, generating massive diarrhea.

Cholera patients, in the secretory active phase of the disease, have elevated concentrations of prostaglandin E2, which has also been shown to stimulate adenylate cyclase and arachidonic acid secretion from membrane phospholipids.

Treatment

The main treatment is based on adequate rehydration until the disease runs its course. Rehydration may be accompanied by intravenous infusion of fluid. Antimicrobial therapy plays a secondary role in reducing the severity of the disease and the duration of time of excretion of the microorganism.

• Intravenous rehydration: For adults, the intravenous replacement solution should be infused as quickly as possible to administer approximately 2 litres in the first 30 minutes. If at this point the patient's clinical condition improves, perfusion can be reduced to administer approximately 100 ml/kg body weight within the first 4 h of therapy. Children in shock should receive 30 ml of intravenous fluid per kg of body weight in the first hour and 40 ml/kg in the next 2 h. In both adults and children, SROs (with their glucose and potassium) should be given as soon as possible in the course of the disease. Precise liquid management rates should be adjusted according to the control of the patient's hydration status and continuous feces losses.
• Oral rehydration: Patients with mild or moderate dehydration may receive initial liquid replacement to repair water deficits and electrolytes exclusively by mouth. For mild dehydration, WHO recommends managing SRO in a volume of 50 ml/kg within the first 4 h. For moderate dehydration, the double of this volume (100 ml/kg) should be administered in the same period of time. Vomits rarely prevent the successful use of SRO and are not a contraindication for use.
• Antimicrobial therapy: The treatment should be started by disappearing vomiting. Tetracycline is the antibiotic of choice.

Adult dose: Doxycycline 300mg orally single dose alternative Tetracycline 500mg every 6 hours for 3 days or trimethosterone-sulfamethasone 80/400mg every 12 hours for 5 days.

Dose in children: 10 to 14 years 200 mg doxycycline single dose. 5 to 9 years 100 mg doxycycline single dose. less than 5 years old erythromycin 30mg/kg for 3 days.

Diagnosis

Samples for culture consist of taking some mucus from the feces and culture them on TCBS agar which produces yellow colonies that are easily visible against the dark-green background of the agar. If the oxidase test for the Vibrio cholerae bacterium is positive, it has detected a gram negative organism.