General characteristics and morphology
The genus Vibrio belongs to the family Vibrionaceae. These are Gram-negative rods with a characteristic curved shape, measuring 1.4–5.0 × 0.3–1.3 µm. They do not form spores or capsules, but are highly motile due to a polar flagellum (monotrichous).
By type of nutrition, vibrios are chemoorganotrophs with oxidative and fermentative metabolism. Most representatives are oxidase-positive. An important biochemical marker of the genus is the ability to ferment carbohydrates (maltose, mannose, trehalose) exclusively to acid, without gas production. They inhabit everywhere: in fresh and salt water bodies, as well as in the organisms of hydrobionts.
Cultural properties and biochemistry
Vibrios are facultative anaerobes, but prefer aerobic conditions. They are not very fastidious regarding nutrient media; however, a high pH level (optimum 8.5–9.0) and the presence of salts are critical for their growth.
- Enrichment medium: 1% alkaline peptone water. Vibrios grow very rapidly in it, forming a characteristic surface pellicle within 6–8 hours.
- Differential diagnostic medium: TCBS (thiosulfate-citrate-bile salts-sucrose agar). On this medium, pathogenic vibrios form yellow colonies due to sucrose fermentation.
Biochemically, vibrios are very active: they produce indole and lysine decarboxylase, liquefy gelatin (forming a "funnel-shaped" zone), and possess nitrate reductase activity, but do not produce hydrogen sulfide.
Causative agent of cholera (Vibrio cholerae)
Cholera is an acute, highly dangerous quarantine infection affecting the small intestine, leading to severe water-electrolyte metabolism disorders and dehydration. The causative agents are serogroups O1 and O139.
Within the O1 serogroup, two main biovars are distinguished:
- Classical (V. cholerae classical) — lysed by group IV bacteriophages.
- El Tor (V. cholerae El Tor) — resistant to polymyxin, gives a positive Voges–Proskauer reaction, hemolyzes sheep erythrocytes, and is lysed by group V bacteriophages.
The main virulence factor is the cholera enterotoxin (CT), consisting of subunits A and B. Subunit B binds to monosialoganglioside GM1 on intestinal cells. Toxin synthesis is encoded by the CTX bacteriophage gene. The phage enters the bacterium via toxin-coregulated pili (TCP) of type 4, which are also responsible for colonizing intestinal microvilli and biofilm formation.
Halophilic and non-halophilic vibrios
In addition to Vibrio cholerae, other members of the genus are of medical significance:
- Halophilic vibrios (e.g., V. parahaemolyticus). Inhabit sea water (optimal salt concentration 2–3%). Transmitted alimentarily via thermally unprocessed seafood and cause severe gastroenteritis.
- Non-halophilic vibrios (V. cholerae non-O1/O139). Inhabit fresh water bodies. They are not agglutinated by O1 and O139 antisera, but can produce heat-labile and heat-stable toxins, causing sporadic diarrheas and even systemic diseases up to septicemia.
Briefly: answers to topical questions
What are the functions of subunits A and B of cholera enterotoxin?
The cholera enterotoxin subunits perform binding and enzymatic functions.
- Subunit B — is responsible for binding the entire toxin molecule to the target cell receptor (monosialoganglioside GM1) and fixes the complex on the membrane.
- Subunit A — is the active part that dissociates into enzyme A1 and linking element A2. Subunit A1 penetrates inside the cell, inactivates the Gs protein, and converts the enzyme adenylate cyclase into a permanently active state.
What is the antigenic structure of the cholera vibrio and which serovars are distinguished within the O1 serogroup?
Cholera vibrio has two types of antigens: the genus-common flagellar H-antigen and the somatic O-antigen. Cholera causative agents belong to serogroups O1 and O139. Within the O1 serogroup, based on the combination of antigen subunits (A, B, C), three serovars are distinguished:
- Ogawa (Ogawa) — contains fractions AB.
- Inaba (Inaba) — contains fractions AC.
- Hikojima (Hikojima) — contains fractions ABC.
Which aggression enzymes, besides exotoxin, does Vibrio cholerae produce?
In addition to exoenterotoxin, sources indicate that Vibrio cholerae produces neuraminidase, hemolysins, and exhibits proteolytic properties.
- Neuraminidase — cleaves sialic acid from GM1, making the receptor accessible for binding with toxin B-subunits.
- Hemolysins and other factors — act synergistically with exoenterotoxin; for the El Tor biovar, the ability to hemolyze sheep erythrocytes is indicated.
- Proteolytic properties — produces indole and lysine decarboxylase, liquefies gelatin.
Which species of halophilic vibrios, besides V. parahaemolyticus, cause human diseases?
In addition to Vibrio parahaemolyticus, a group of halophilic vibrios provoking septicemias and wound infections causes human diseases:
- Vibrio vulnificus (Vibrio vulnificus) — causes wound infections and primary sepsis (especially in individuals handling seafood and immunocompromised patients).
- Vibrio damsela (Vibrio damsela) — causative agent of septicemias and wound infections.
- Vibrio alginolyticus (Vibrio alginolyticus) — also causes septicemias and wound infections.
What is the intracellular mechanism of action of cholera toxin on enterocytes?
The intracellular mechanism of action of cholera toxin is based on the disruption of ion transport via hyperactivation of secondary messengers. Subunit A1, having penetrated the enterocyte, inactivates the Gs protein, which converts the adenylate cyclase enzyme into a permanently active state. This causes a dramatic increase in cAMP synthesis. Concurrently, cGMP synthesis is suppressed. As a result, enhanced secretion of chloride and sodium ions into the intestinal lumen is triggered in the crypts, while their reabsorption is blocked in the villi. This creates high osmotic pressure, leading to massive water efflux and the development of secretory diarrhea.
What are the optimal pH and temperature values for cultivating Vibrio cholerae?
The optimal conditions for cultivating Vibrio cholerae are an alkaline medium and human body temperature.
- Temperature: the optimal value is 37 °C.
- Acidity (pH): optimal values are within 8.5–9.0 (the pathogen prefers an alkaline environment).
To enrich the pathogen, 1% alkaline peptone water is used as an elective medium.
To remember V. cholerae serovars O1 by antigen fractions: Ogawa — AB, Inaba — AC, Hikojima — ABC (the longest name includes all three letters).
Class and exam questions
Why do Vibrio cholerae colonies on TCBS medium appear yellow?
The yellow color of the colonies is due to the vibrio's ability to ferment sucrose present in the differential diagnostic medium.
What are the fundamental differences between the El Tor biovar and the classical biovar of Vibrio cholerae?
El Tor biovar is resistant to polymyxin, capable of agglutinating chicken erythrocytes, hemolyzes sheep erythrocytes, and is lysed by group V phages, whereas the classical biovar is lysed by group IV phages.
What is the role of toxin-coregulated pili (TCP) in Vibrio cholerae?
They are responsible for adhesion to intestinal microvilli, participate in biofilm formation, and serve as receptors for the entry of the CTX bacteriophage carrying the cholera toxin gene.
What else to study on this topic
- Mechanism of action and structure of cholera enterotoxin (A and B subunits)
- Colony dissociation of vibrios (S and R forms) depending on temperature
- Serological diagnostic methods for cholera (IHA, ELISA)
- Pathogenicity factors of non-halophilic vibrios (cytolysins, hemolysins)
Study the full topic in the «Microbiology» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Vibrios" and 4,383 other pages for this subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 141 video lectures on the subject
Other topics in the section "Gram-negative facultatively anaerobic rods (Enterobacteriaceae, Vibrio, Haemophilus, Pasteurella)"
Free video lessons: microbiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.