VIBRIO: CHARACTERISTICS, MORPHOLOGY, SPECIES, PATHOLOGIES - BIOLOGY - 2024

The vibrio are a group of gram - negative eubacteria. Bacteria recognized as vibrios belong to the Vibrio genus, which together with seven other genera make up the Vibrionaceae family.

Many of the representatives of the genus Vibrio are not "choleric", that is, they are not pathogenic. However, of the great diversity of species that make it up, about 12 cause diseases in man.

Source: Tom Kirn, Ron Taylor, Louisa Howard - Dartmouth Electron Microscope Facility

Most of the species are found in aquatic environments such as estuaries, brackish lagoons and in marine environments, supporting conditions with high salinity, generally having halophilic behavior.

characteristics

The main mechanism of infection with these bacteria is due to the consumption of contaminated food from marine sources. These bacteria tend to increase in number when the water temperature is ideal (17 ° C to 20 ° C) which increases the probability of infection during the summer.

Vibrios easily grow in almost all isolation media. Due to the halophilic characteristic of many of the species, they tend to grow better and faster in media with 1% NaCl. The species that have not been related to pathologies in humans are known as "marine vibrio".

The representatives of the Vibrionaceae family are non-enteric bacteria, that is, their frequent habitat is not the intestines of animals and man, being generally free-living.

These bacteria are oxidase positive, which indicates that they possess cytochrome C oxidase and can use oxygen to generate energy in the electron transport chain, a characteristic that separates them from Enterobacteriaceae. They are also facultative anaerobes, with certain capacities to ferment.

Vibrios produce a number of toxins including tetrodotoxin and saxitoxin as well as enterotoxins such as those related to cholera.

Morphology

Bacteria belonging to this group are grouped into the Vibrionaceae family, currently consisting of eight genera according to several recent molecular studies. Of these genres one of the most outstanding is Vibrio due to its importance in man.

Individual bacterial cells have a typical coma shape, which is why they are also called "coma bacilli" and are characterized by having a single polar flagellum that gives them great motility, which is why they were called vibrios.

Like many gram-negative bacteria, its bacterial wall consists of a thin layer of peptidoglycans and an outer membrane with an intricate network of lipopolysaccharides, phospholipids, lipoproteins and various polysaccharides, which protect the microorganism from external agents.

Important species

The Vibrionaceae family includes several species that cause intestinal and extraintestinal tract infections in both humans and animals.

Species that are isolated from humans and potentially cause disease can be divided into two groups: Vibrio cholerae and non-cholera vibrios.

The three primary Vibrio species associated with food contamination that are often marine in origin are: Vibrio cholerae, V. parahemolyticus, and V. vulnificus.

Vibrio cholerae

This species is the causative agent of cholera in humans. Many have been the pandemics caused by this bacterium, counting from the 18th century to seven in total. The most recent was in 1961 that began in Indonesia and reached South and Central America 30 years later, caused by V. cholerae 01 “El Tor Biotype”.

Other minor epidemics have been caused by other serotypes No. 01 and by other recently described halophilic species, generally associated with the consumption of marine products such as contaminated or poorly cooked and processed seafood.

Other pathologies such as infected wounds have been attributed to the species, when swimming in polluted waters or being exposed to marine animals.

Different strains of V. cholerae have different pathogenic and epidemic potential. These are divided according to the composition of their cell wall (somatic "O" antigen) that forms the basis for serotyping that classifies these microorganisms into 139 different serogroups.

They all share the common flagellar (H) antigen, which makes serotype identification difficult by this means.

Pathogenesis

All pandemic strains are agglutinated with a single antiserum designated O1. The latter can also be separated into 3 serogroups: Inaba, Ogawa and Hikojima, and each serogroup can be classified into two biotypes, the classical and the “tor” biothiope, which is more resistant and capable of surviving in the environment.

The el Tor biotype is an actively hemolytic strain. An eighth pandemic could be attributed to toxigenic serotype 0139 Bengal.

Non-choleric vibrios

Although many species of Vibrio are called "non-choleric", they can also cause diarrhea. These species also produce enterotoxins similar to those described for V. cholerae. However, most infections turn out to be less serious and of shorter duration.

Among the non-choleric vibrios are the Vibrio alginolyticus species, also of marine habits, it is associated with soft tissue infections and infection of superficial wounds of the skin and ears due to exposure to contaminated seawater.

The species V. fluvialis, V. furnissii, V. hollisae, V. mimicus, V. parahaemolyticus, are mostly associated with the production of diarrheal syndromes in some situations similar to cholera, as well as gastroenteritis and dehydration.

In V. hollisae, invasion of the circulatory system has been reported in patients with liver deficiencies. Other symptoms include nausea, vomiting, abdominal pain, fever, and chills.

V. metschnikovii and V. vulnificus are associated with cases of septicemia and urinary tract infections. In Vibrio vulnificus infections, septicemia can be life threatening. In addition, they can also produce some enterotoxins similar to those described for cholera that cause diarrheal diseases.

Pathologies

The pathogenic action of vibrio toxin is not to alter or damage the intestinal mucosa. The pathogenic action of the toxin intervenes on the normal mechanisms of the cells of the intestinal epithelium that regulate the absorption and secretion mechanisms of fluids and electrolytes.

Cholera (

Cholera is one of the best known pathologies caused by bacteria of the Vibrio genus. The generation of a severe diarrheal syndrome is due to the fact that this bacterium secretes a powerful enterotoxin that consists of two subunits. An active A subunit and a binding B.

The first is composed of two peptides, A1 with toxin activity and A2 that facilitates the penetration of the A subunit into the cell. On the other hand, the B subunit binds the toxin molecule to the cholera toxin-specific GM1 ganglioside receptors on the membrane of the epithelial cells of the small intestine.

After a series of steps, A1 produces a drastic elevation of the intracellular content of cAMP. The latter prevents the reabsorption of sodium ions through the membrane of the intestinal epithelial cells and the excretion of sodium and potassium bicarbonate into the intestinal lumen.

The ionic concentration gradient caused in the intestinal chyle causes water to leave the epithelial cells and accumulate in the intestine and be evacuated due to severe diarrhea.

This can lead to severe dehydration and an electrolyte imbalance leading to metabolic acidosis, hypokalemia, shock, and death if left untreated.

Extraintestinal infections

The most common extraintestinal infections caused by Vibrio are skin wound infections or external otitis caused by contamination of the skin by swimming in contaminated water or by handling contaminated food, which can lead to fatal septicemia as in the aforementioned case of infection with V. vulnificus.

References

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