BCM 312: Clinical Biochemistry of Cholera and HIV

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16 Questions

Which bacterium is responsible for causing cholera?

Vibrio cholerae

When was the El Tor biotype of V cholerae first isolated?

1905

How many cholera pandemics have occurred since 1817?

7

Which serogroup caused the epidemic of cholera in Madras, India in October 1992?

0139

Where did the seventh pandemic of cholera begin in 1961?

Indonesia

Why is the number of cholera patients worldwide uncertain?

Most cases go unreported

What is the size range of the V. cholerae organism?

1-3 mm in length by 0.5-0.8 mm in diameter

What is the antigenic structure of the V. cholerae organism?

Flagellar H antigen and somatic O antigen

What causes the dramatic increase in cAMP levels within the cell in V. cholerae infection?

ADP-ribosylation of the Gs α subunit by the toxin

What is the consequence of the sustained activation of adenylate cyclase in V. cholerae infection?

Dramatic increase in cAMP levels within the cell

What is the role of cAMP in V. cholerae infection?

Activates cAMP-dependent protein kinase (protein kinase A, PKA)

Which receptor do the B subunits of the toxin bind to on the epithelial cells lining the gut?

Ganglioside receptor GM1 (GM1)

What is responsible for separating V. cholerae into pathogenic and nonpathogenic strains?

Antigenic structure consisting of a flagellar H antigen and a somatic O antigen

What causes net fluid loss leading to watery diarrhea in V. cholerae infection?

Decrease in chloride and bicarbonate movement out of the cell

What causes a decrease in sodium influx into the cell during V. cholerae infection?

Increase in chloride and bicarbonate movement out of the cell

What is secreted by V. cholerae in the small intestine of affected individuals?

Toxin consisting of an active A subunit attached to a ring of five B subunits

Study Notes

Cholera

  • Caused by the bacterium Vibrio cholerae

History of Cholera

  • El Tor biotype of V. cholerae first isolated in 1905
  • Seven cholera pandemics have occurred since 1817

Epidemics

  • 1992 epidemic in Madras, India caused by serogroup O1
  • Seventh pandemic of cholera began in 1961 in Indonesia, Sulawesi

Characteristics of V. cholerae

  • Size range: 1-3 μm x 0.2-0.5 μm
  • Antigenic structure: lipopolysaccharide (LPS) and polysaccharide capsule

Pathogenesis of V. cholerae Infection

  • Dramatic increase in cAMP levels within the cell caused by ADP-ribosylation of Gsα
  • Sustained activation of adenylate cyclase leads to increased cAMP production
  • cAMP enhances Cl- secretion and inhibits Na+ absorption, leading to secretory diarrhea
  • B subunits of the toxin bind to GM1 receptor on epithelial cells lining the gut

Pathogenicity

  • Presence of ctx and zot genes responsible for separating V. cholerae into pathogenic and nonpathogenic strains

Clinical Manifestations

  • Net fluid loss leading to watery diarrhea caused by increased Cl- secretion and inhibited Na+ absorption
  • Decreased sodium influx into the cell due to inhibition of NHE by cAMP
  • V. cholerae secretes cholera toxin in the small intestine of affected individuals

This quiz covers the biochemistry of cholera, including its etymology, causative agent V. cholerae, major biotypes, and epidemiology. It also includes background information about the discovery of V. cholerae and the history of cholera pandemics. Additionally, the quiz delves into the biochemistry of HIV.

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