Vibrio Cholerae and Cholera Disease

Study Notes

Gram-negative: This bacterium is gram-negative.
Oxidase-positive: It exhibits a positive oxidase reaction.
Motile rods: The bacteria are motile and rod-shaped.
Salt-tolerant: Some strains are tolerant of high salt concentrations.
Salt-requiring: Some strains require salt for growth.
Freshwater/brackish water: The bacteria are commonly found in fresh and brackish water environments.
Comma shape rods: The bacteria's distinctive rod shape is somewhat comma-like.
Culture: It can be cultured on various media commonly used for stool cultures.
Cholera Disease: Vibrio cholerae is the causative agent of cholera.

Fecal-oral route: The primary route of transmission is through ingesting contaminated food or water that contains the bacteria's stool.
Contaminated food/water: Eating contaminated food or drinking contaminated water can lead to infection.
Large inocula: Relatively high numbers of bacteria are typically needed to establish an infection.
Person-to-person: Direct contact between people is not a significant mode of transmission.
Reservoir: Recovered cholera patients can shed the bacteria and act as a reservoir, especially in endemic regions.

Incubation period: The time between ingestion and the onset of symptoms is 6 hours to 3 days.
Sequence of events: Ingestion -> adherence and colonization -> secretion of toxins -> fluid and electrolyte loss.
Adherence and colonization: Virulent forms attach to the small intestinal epithelium, specifically microvilli.
Multiplication: The bacteria multiply after crossing the acid barrier.
Cholera toxin secretion: The bacteria release a potent toxin, called enterotoxin.
Specific receptors: The toxin binds to specific GM1 ganglioside receptors on the small intestine cells.

B subunit binding: The B subunit binds to the cell membrane receptor.
A subunit dissociation: The A subunit detaches from the B subunit.
Membrane penetration: The cell membrane is penetrated during this process.
A1/A2 subunits: The A subunit is composed of the A1 and A2 subunits linked by a disulfide bond.
ADP-ribose transfer: Activated A1 subunit transfers part of the NAD molecule to a GTP binding protein.
Adenyl cyclase activation: This process stimulates adenyl cyclase activity, increasing the cell's cAMP levels.

Intracellular cAMP increase: The increased cyclic AMP (cAMP) within the cells results from the previous events.
Inhibition of reabsorption: cAMP inhibits the reabsorption of sodium, potassium and chloride ions.
Hypersecretion: It increases the secretion of chloride and bicarbonate ions.
Net loss of electrolytes: The combined effects lead to a significant loss of fluids and electrolytes.
"Rice water stool": The severe diarrhea which is characteristic of cholera.

Isotonic with plasma: The secreted fluid has a comparable solute concentration to blood plasma.
Electrolyte imbalance: High sodium, potassium and bicarbonate but low chloride levels.
Consequences: The loss of fluids result in dehydration, acidosis, shock, and potential death if not addressed rapidly.

Symptoms: Sudden vomiting and profuse watery diarrhea accompanied by abdominal cramps, mucus-containing stool, rapid electrolyte loss leading to dehydration, circulatory collapse and anuria.
Complications: Dehydration, circulatory shock and kidney failure (anuria).
Mortality: The fatality rate is 25-50% without treatment.

Stool/vomitus culture: A laboratory test that can identify the bacteria and confirm the infection.

Fluid replacement: Essential for addressing dehydration and electrolyte imbalances.
Electrolyte replacement: Important to restore the body's lost electrolytes.
Antimicrobial drugs: Effective antibiotics like oral tetracycline used to reduce the duration and severity of infection.

Public sanitation: Crucial to prevent the contamination of water sources.
Water purification: Boiling water is an effective method to eliminate the bacteria.
Food safety: Handling and preparing food safely can also prevent widespread contamination.
Vaccination: Limited effectiveness and only provides short-term protection.
Hygiene: Handwashing is a vital step to prevent the spread of the bacteria.