Vibrio cholerae: Morphology and Identification, Antigenic Structure and Biologic Classification, Vibrio cholerae Enterotoxin, Pathogenesis and Pathology, Flashcards
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Vibrio cholerae: morphology and identification
Vibrio cholerae is a Gram-negative, comma-shaped (curved) bacillus with a single polar flagellum, which makes it highly motile. It grows well on alkaline agar media, such as thiosulfate-citrate-bile salts-sucrose (TCBS) agar, where it produces yellow colonies due to sucrose fermentation. It is oxidase-positive and does not ferment lactose.
Vibrio cholerae: antigenic structure and biologic classification
Vibrio cholerae is classified into two biogroups: El Tor and classical. It has a distinctive O antigen in its lipopolysaccharide (LPS) that plays a key role in its immunogenic properties. There are over 200 serogroups of V. cholerae, but serogroups O1 and O139 are primarily responsible for cholera outbreaks. It also produces a cholera toxin which is crucial for its pathogenicity.
Vibrio cholerae: Vibrio cholerae enterotoxin
Vibrio cholerae produces a potent enterotoxin called cholera toxin (CT), which is composed of two subunits: A and B. The B subunit binds to gangliosides on intestinal epithelial cells, facilitating the entry of the A subunit into the cells. The A subunit activates adenylate cyclase, increasing cyclic AMP levels, which leads to massive secretion of water and electrolytes, causing diarrhea.
Vibrio cholerae: pathogenesis and pathology
The pathogenesis of V. cholerae involves the ingestion of contaminated water or food. The bacteria colonize the small intestine, where cholera toxin disrupts normal cellular function by increasing cyclic AMP levels. This results in severe fluid loss, leading to dehydration and electrolyte imbalance. The infection does not cause tissue invasion, but the massive diarrhea can lead to shock and death if untreated.
Vibrio cholerae: clinical findings
Cholera typically presents with sudden onset of profuse, watery diarrhea (often described as ‘rice-water stool’), vomiting, and dehydration. Patients can quickly develop hypovolemic shock, with symptoms such as dry mucous membranes, decreased skin turgor, sunken eyes, and rapid pulse. In severe cases, death can occur due to electrolyte imbalances and dehydration.
Vibrio cholerae: diagnostic laboratory tests
Diagnosis of cholera involves stool culture on selective media like TCBS agar, where V. cholerae produces characteristic yellow colonies. Serologic testing can confirm the O1 or O139 serogroups. PCR-based assays and enzyme immunoassays (EIAs) are also available for rapid detection of cholera toxin. The diagnosis is often made clinically in endemic areas based on symptoms.
Vibrio cholerae: treatment
Cholera is treated primarily with rehydration therapy, using oral rehydration salts (ORS) or intravenous fluids in severe cases. Antibiotics such as doxycycline or azithromycin may be used in severe cases to reduce the duration of diarrhea and the bacterial load. Zinc supplementation can also be used to reduce the severity and duration of diarrhea in children.
Vibrio cholerae: epidemiology
Cholera is endemic in many parts of the world, especially in areas with poor sanitation and limited access to clean water, such as parts of Africa, Asia, and Latin America. The disease is transmitted via the fecal-oral route, often through contaminated water or food. Cholera outbreaks are typically associated with inadequate sanitation and during times of natural disasters or war.
Vibrio cholerae: prevention and control
Prevention of cholera involves ensuring access to clean drinking water, improving sanitation and hygiene, and promoting handwashing. Cholera vaccines, such as oral cholera vaccine (OCV), are available and are recommended in high-risk areas. Control measures during outbreaks include the rapid provision of rehydration therapy, improving water and sanitation infrastructure, and isolating affected individuals.
