Vibrio cholerae

''Vibrio cholerae'' is a species of Gram-negative, facultative anaerobe and comma-shaped bacteria. The bacteria naturally live in brackish or saltwater where they attach themselves easily to the chitin-containing shells of crabs, shrimps, and other shellfish. Some strains of ''V. cholerae'' are pathogenic to humans and cause a deadly disease cholera, which can be derived from the consumption of undercooked or raw marine life species.

''V. cholerae'' was first described by Félix-Archimède Pouchet in 1849 as some kind of protozoa. Filippo Pacini correctly identified it as a bacterium and from him, the scientific name is adopted. The bacterium as the cause of cholera was discovered by Robert Koch in 1884. Sambhu Nath De isolated the cholera toxin and demonstrated the toxin as the cause of cholera in 1959.

The bacterium has a flagellum at one pole and several pili throughout its cell surface. It undergoes respiratory and fermentative metabolism. Two serogroups called O1 and O139 are responsible for cholera outbreaks. Infection is mainly through drinking contaminated water, therefore is linked to sanitation and hygiene. When ingested, it invades the intestinal mucosa can cause diarrhea and vomiting in a host within several hours to 2–3 days of ingestion. Oral rehydration solution and antibiotics such as fluoroquinolones and tetracyclines are the common treatment methods.

''V. cholerae'' has two circular DNA. One DNA produces the cholera toxin (CT), a protein that causes profuse, watery diarrhea (known as "rice-water stool"). But the DNA does not directly code for the toxin as the genes for cholera toxin are carried by CTXphi (CTXφ), a temperate bacteriophage (virus). The virus only produces the toxin when inserted into the bacterial DNA.

Quorum sensing in ''V. cholerae'' is well studied and it activates host immune signaling and prolongs host survival, by limiting the bacterial intake of nutrients, such as tryptophan, which further is converted to serotonin. As such, quorum sensing allows a commensal interaction between host and pathogenic bacteria.

Discovery

Initial observations

During the third global pandemic of cholera (1852–1859), there were several scientific research to understand the etiology of the disease. The miasma theory, which posited that infections spread through contaminated air, was no longer a satisfactory explanation. An English physician John Snow was the first to give convincing evidence in London in 1854 that cholera was spread from drinking water – a contagion, not miasma. Yet he could not identify the pathogens, which made most people still believe in the miasma origin.

''V. cholerae'' was first observed and recognized under microscope by a French zoologist Félix-Archimède Pouchet. In 1849, Pouchet examined the stool samples of four people having cholera. His presentation before the French Academy of Sciences on 23 April was recorded as: " ouchetcould verify that there existed in these holera patientsdejecta an immense quantity of microscopic infusoria." But he made a mistake in believing that the organisms were infusoria, a name then used for microscopic protists, thereby attributing them as ''Vibrio rigula,'' a species of protozoan described by Danish naturalist Otto Friedrich Müller in 1786.

Identification of the bacterium

An Italian physician, Filippo Pacini, while investigating cholera outbreak in Florence in the late 1854, identified the causative pathogen as a new type of bacterium. He performed autopsies of corpses and made meticulous microscopic examinations of the tissues and body fluids. From feces and intestinal mucosa, he identified many comma-shaped bacilli. Reporting his discovery before the Società Medico-Fisica Fiorentina (Medico-Physician Society of Florence) on 10 December, and published in the 12 December issue of the ''Gazzetta Medica Italiana'' (''Medical Gazette of Italy''), Pacini stated:Pacini thus introduced the name ''vibrioni'' (Latin ''vībro'' means "to move rapidly to and fro, to shake, to agitate"). A Catalan physician Joaquim Balcells i Pascual also reported such bacterium around the same time. The discovery of the new bacterium was not regarded as medically important as the bacterium was not directly attributed to cholera. Pacini also stated that there was no reason to say that the bacterium caused the disease since he failed to make pure culture and perform experiment, which was necessary 'to attribute the quality of contagion to cholera'. The miasma theory was still not ruled out.

Rediscovery

The medical importance and relationship of the bacterium and cholera was discovered by a German physician Robert Koch. In August 1883, Koch, with a team of German physicians, went to Alexandria, Egypt, to investigate cholera epidemic there. Koch found that the intestinal mucosa of people who died of cholera always had the bacterium, yet could not confirm if it was the causative agent. He moved to Calcutta (now Kolkata) India, where the epidemic was more severe. It was from here that he isolated the bacterium in pure culture on 7 January 1884. He subsequently confirmed that the bacterium was a new species, and described as "a little bent, like a comma." He reported his discovery to the German Secretary of State for the Interior on 2 February, and published in the ''Deutsche Medizinische Wochenschrift'' (''German Medical Weekly'').

Although Koch was convinced that the bacterium was the cholera pathogen, he could not entirely establish a critical evidence the bacterium produced the symptoms in healthy subjects (an important element in what was later known Koch's postulates

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