31- Vibrios Flashcards
What is the mechanism of action of the cholera toxin?
• Cholera toxin is composed of two subunits, ctxA and ctxB. These subunits are encoded by genes from a bacteriophage. The cholera A-B toxin is structurally and functionally similar to the heat-labile enterotoxin of E. coli. A ring of five identical B subunits binds to the GM1 receptors of the intestinal epithelia cell. Active portion of the A subunit is internalized and interacts with G proteins. The G proteins, when interacting with the toxin, cause the conversion of ATP to cAMP through adenylate cyclase. This results in the hypersecretion of water and electrolytes.
How do you ascribe nomencature to cholera?
• Vibrio are named and subdivided according to the O-polysaccharide side chain. V. cholera O1 and 0139 produce cholera toxin and are associated with epidemics of cholera. Other strains of cholera do not produce toxin and are not associated with epidemic disease
Cholera- epidemiology
• Vibrio species grow naturally in estuarine and marine environments worldwide. All vibrio species are able to survive in contaminated waters with increased salinity. Asymptomatic humans can also be an important reservoir for vibrio species like cholera. Cholera is spread by contaminated water and food. Direct person to person spread is unusual because a high innoculum is required (e.g. more then 10 to the 8th organisms) to establish infection in person with normal stomach acid. Cholera is usually seen in the communities with poor sanitation.
V. parahaemolyticus- clinical presentation
o This usually causes gastroenteritis, explosive diarrhea and nausea, vomiting, and a low grade fever. It is spread by contaminated water in wound infections, but more commonly spread through seafood, more particularly shellfish.
V. vulnificus- clinical presentation
o This can lead to a particularly fatal infection which can lead to necrosis of tissue and septicemia. It is usually spread by exposure to contaminated waters to wounds. It can also spread by means of seafood, like shellfish.
V. cholera- clinical presentation
o This usually causes a milder case of gastroenteritis. It begins with an onset of diarrhea and vomiting and can lead to severe dehydration, metabolic acidosis, hypokalemia, and hypovolemic shock. Rice water stools are seen. Usually cholera is spread by intake of contaminated water.
Why are vibrios different than enterics as far as lab features?
• Vibrios can be differentiated on the basis of a positive oxidase reaction and presence of polar flagella. Enterics are also gram negative rods, but are oxidase negative. Vibrios tend to have a single polar flagellum while enterics have peritrichous flagella. Vibrios species are small gram-negative rods that cannot be differentiated from other enteric organisms. No direct microscopic examination of stool specimens can be used. Vibros survive poorly in acidic or dry environment. Specimens must be collected early in the disease and inoculated promptly. Will grow on special agar for vibrios TCBS agar
