Vibrios

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Vibrios
Tropical Medicine 604 Alan Garcia
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Vibrios

• More than 60 species
• 10 species cause human infections
• V. cholerae
• V. vulnificus
• V. parahaemolyticus
• V. alginoliticus

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Vibrios

• Sources
• Human primary reservoirs/carriers
• Animal - zooplankton
• Food mainly seafood
• Environment aquatic reservoirs

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Physiology and Structure

• Found in fresh and salt water
• Characteristics
• Gram-negative
• straight or curve rods with a polar flagella.
• facultative anaerobes
• grows at pH as high as 9.0
• display a wide range of halotolerance

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Cholera El Tor Pandemic

• The seventh pandemic of cholera, 1961
• Strain known as El Tor
• Spread throughout Indonesia, India, and to Italy
  in 1973
• Reached South America in 1991, caused an epidemic
  in Peru

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Cholera Today

• Africa
• 120,000 cases
• 4500 deaths
• Asia
• 11,000 cases
• 200 deaths
• America
• 3000 cases
• 40 deaths

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V. cholerae Basics

• V. cholerae
• Gram-negative
• 2 chromosomes
• Polar monotrichous
• Curved rod
• Ferments glucose,
• sucrose, and mannitol

Heidelberg, J. F. et al. 2000. DNA sequence of
both chromosomes of the cholera pathogen Vibrio
cholerae Nature. 406, 477-483.
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Classification Scheme
Division into 2 epidemic serotypes
Classical
El Tor
Each O1 biotype can have 3 serotypes
Division into ribotypes
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Known Virulence Factors

• Integrons
• Toxins
• Cholera Toxin (CT)
• Hemmagglutinin Protease
• Zonnula occludens toxin (Zot)
• Accessory cholera enterotoxin (ACE)
• Adherence/Adhesins
• Accessory Colonization Factors (ACF)
• Outer membrane proteins U (OmpU)
• Toxin Co-regulated Pilus (TCP)

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Cholera Toxin (CT)

• Heat labile enterotoxin
• Comprises two subunits,
• A and B, arranged in a AB5
• conformation
• Binds to Gm1 gangliosides
• A portion is internalized and interacts with G
  proteins
• Conversion of ATP ? cAMP
• Hyperproduction of cAMP causes hypersecretion of
  water and electrolytes

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AB5 Exotoxins
Murray et al., 2005. Medical Microbiology 5e
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Quorum Sensing

• Cellular signaling in bacteria
• Chemical molecules (autoinducers)
• - Involves acyl homoserine lactones (AHLs)
• Alter bacteria gene expression
• Bacteria population act as a collective unit

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Quorum Sensing

• Kaper J.B. and Vanessa Sperandio. 2005. Bacterial
  Cell-to-Cell Signaling in the Gastrointestinal
  Tract. Infection and Immunity. 73 (6)
  3197-3209

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Quorum Sensing (QS)

• QS aid in disease process
• grow to high cell densities before virulence
  determinants are expressed
• disease may vary among individuals due to
  variable levels of QS activity

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QS signaling cascade in V. cholerae
Repression at high densities and expression at
low cell densities.

• Kaper J.B. and Vanessa Sperandio. 2005. Bacterial
  Cell-to-Cell Signaling in the Gastrointestinal
  Tract. Infection and Immunity. 73 (6)
  3197-3209

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Clinical Manifestations
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Clinical disease

• The illness
• incubation 6hrs to 5 days
• sudden onset of vomiting painless diarrhea
• rice water stools
• severe dehydration death
• infective dose 106
• all individuals susceptible

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Clinical Disease
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Diagnosis

• Clinical
• Diarrhea (20L/day)
• Laboratory
• Culture-based methods using fecal or water
  samples
• Dark-field microscopy
• Molecular methods - PCR
• DNA probes

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Treatment

• Fluid and electrolyte replacement
• Water
• NaCl
• Glucose
• Antibiotics
• Doxyclcline
• Tetracycline

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Cholera Vaccine

• Desired vaccine
• Live attenuated whole cell
• Killed whole cell
• Whole cell recombinant B subunit
• Ideal Vaccine
• Single dose offering degree of long-term
  protection.
• Vaccine administration
• Oral route
• Target Children
• Vaccine should contain all biotypes and serotypes
• Inaba, Ogawa, Hikojima

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Preventing Cholera Vaccines

• Orochol
• Contains 2x108 viable cells of attenuated strain
  CVD 103-HgR in a lyophilized form
• Oral immunization of children older than 2
• Subunit A of the cholera toxin (CT) has been
  removed
• Dukoral
• Protects against O1 Inaba
• and Ogawa, Classical El
• Tor strains
• Contains 1x10 heat/formalin
• killed cells of strain WC/rBS

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Epidemic Control Measures

• Hygienic disposal of human waste
• Adequate supply of water
• Good food hygiene
• Thoroughly cooking food
• Eating food while its hot
• Preventing cooked foods from contacting raw foods
  (including water or ice)
• Avoiding raw fruits or vegetables
• Washing hands after defecation before cooking

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Prevention

• Filtration
• Pouring water through an old piece of sari cloth,
  folded at least 4X reduced the number of cases in
  a Bangladeshi village

Colwell RR et al., 2003 PNAS 100 (3) 1051-1055
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Vibrio parahaemolyticus

• Most often associated with eating
  raw/contaminated seafood.
• Common cause of GI disease in Japan
• US infections are Seasonal
• 70 occur between May and October
• Environmental factors, such as warm water and
  moderate salinity, can increase the number of
  organisms in shellfish.

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Vibrio parahaemolyticus

• Watery diarrhea, often with abdominal cramping,
  nausea, vomiting, and fever.
• Most persons recover after 3 days and suffer no
  long-term consequences.
• Less commonly, wound or soft tissue infections.
• Occasionally bacteremias.

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Vibrio vulnificus

• Commonly found in marine and estuarine
  environments
• Eating raw or undercooked shellfish, particularly
  oysters harvested from warmer waters.
• Exposure to warm seawater

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Vibrio vulnificus

• Persons with underlying medical conditions,
  especially hepatic diseases
• Wound or soft tissue infections
• Bacteremia
• 50 mortality
• Healthy individuals
• Diarrhea, vomiting, and abdominal pain

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Vibrios alginolyticus

• Found in sea-water where it can cause significant
  infections of the external ear or wounds.
• On rope burns or
• Chronic ulcers in elderly people who bath in
  sea-water.

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References

• Crowcroft NS. 1994. Cholera Current
  Epidemiology. The Communicable Disease Report.
  4(13) R158-R163.
• Colwell RR et. al., 2003 Reduction of cholera in
  Bangladeshi villages by simple filtration. PNAS
  100 (3) 1051-1055
• Heidelberg, J. F. et al. 2000. DNA sequence of
  both chromosomes of the cholera pathogen Vibrio
  cholerae Nature. 406, 477-483.
• Kabir S. 2005. Cholera vaccines the current
  status and problems. Reviews in Medical
  Microbiology. 16 101-116.
• Kaper J.B. and Vanessa Sperandio. 2005. Bacterial
  Cell-to-Cell Signaling in the Gastrointestinal
  Tract. Infection and Immunity. 73 (6)
  3197-3209
• Murray et. al., Medical Microbiology 5e. Chapter
  32

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Study Questions

• Define the mechanism of action of the AB5
  enterotoxin of Cholera Toxin that leads to the
  loss of fluids and electrolytes in an individual?
• What is Quorum Sensing and how does QS in Vibrio
  differ from other bacteria?
• What measures are important in the development of
  a vaccine against V. cholera?
• What precautions can one take in order to prevent
  Vibrio infection?