Download Vibrio Cholerae - Carolinas College

Vibrio Cholerae
Objectives
Following the presentation, the audience will be able to….
• Name the toxin associated with Vibrio cholerae and its
components
• Recall the biochemical tests used to diagnose V.
cholerae
• Determine a successful treatment plan for V. cholerae
• List the two strains associated with classical cholera
• Recognize the timeline of symptoms associated with
cholera
• Theorize about the spread of V. cholerae
General Characteristics
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Curved rod, Gram negative,Facultative anaerobe
Primarily found in water
Causes a gastrointestinal disease
Cause of 7 global pandemics (worldwide epidemics) in
the last 2 centuries
• Epidemic in Dhaka, Bangladesh (est. 30K)
• Usually fairly low frequency except in coastal area’s
• Members of species are subdivided on the basis of their
somatic O antigen (on CW) with more than 200
serotypes to date..O1 (El tor and classical) and O139
(originated in India, 1992) are responsible for classic
cholera
Epidemiology
• Vibrio cholerae grows naturally in estuarine and
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marine environments worldwide
V. cholerae O1 is the causative agent of
cholera, also known as Asiatic cholera or
epidemic cholera
Rare in the U.S.
Can survive and replicate in contaminated
waters with increased salinity at temps (10-30C)
Associated with Chitinous shellfish
Route of Transmission
• Associated with Chitinous shellfish
• Spread by the consumption of contaminated food or
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water (water borne disease) and fecal-oral route is a
possibility
Direct person to person spread is rare because the
infectious dose is high (10^8 organisms)…..most
organisms are killed by stomach acids
Individuals with reduced gastric acidity are more
susceptible to infection
Events such as floods, famine, overcrowding, inadequate
sanitary facilities, favor the outbreak of V. cholerae
Symptoms associated with Cholera
• Causes a gastrointestinal disease
• Once injested, Vibrio organisms colonize the small
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intestine
Severe gastroenteritis
Infection with O1 can range from asymptomatic
colonization or mild diarrheal disease to severe rapidly
fatal diarrhea
Clinical symptoms begin an average of 2 to 3 days after
ingestion of the organism with abrupt onset of watery
diarrhea and vomiting
# of stools may be 10-30 times a day (1L per hr.)
dehydration, hypovolemic shock, and death
Mortality is 60% if untreated but less than 1% when
promptly treated
• Characterized by clear stools with mucus flecks
hence the term “rice water stools”
• Can resolve spontaneously after a few days of
symptoms
Virulence Factor Mechanism
• Choleratoxin or choleragen=powerful endotoxin (virulence factor)
• The choleratoxin consists of two toxic “A” subunits and 5 binding “B”
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subunits
Toxin initially binds to GM1-ganglioside recepter on cell membrane via “B”
units
A2 facilitates entrance for A1—stimulates production of adenylate cyclase
through inactivation of G protein
This leads to an accumulation of cAMP thus a hypersecretion of (Na, K,
HCO3) into lumen
The GI absorptive ability is overwhelmed --- outpouring of stool
As more fluid is lost, the feces-streaked stool specimen becomes colorless
and odorless, free of protein and speckled with mucus giving the classic
“rice water stool”
The severe fluid and electrolyte loss can lead to dehydration, metabolic
acidosis (bi-carbonate loss), hypokalemia, hypovolemic shock with cardiac
arrhythmia and renal failure
Lab Diagnosis
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Small (.5 x 1.5 um), curved G- rod
Organisms are rarely seen in Gram stained stool or wound specimen
Experienced eye can detect the motile bacilli using Darkfield microscopy
Can survive in acidic or dry environments
Specimens should be collected early in disease
Specimens should be mixed in Cary-Blair transport media and refrigerated (if
delayed)
Vibrios grow on media used in clinical labs. for stools including blood(5% sheep
blood) and MacConkey
Selective agar for Vibrio is the TCBS agar (thiosulfate citrate bile salts sucrose agar)
which helps differentiate sucrose fermenting Vibrios (cholera) from non-sucrose
Vibrios
TTGA agar
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• Alkaline peptone broth (enrichment broth) pH 8.6 is good for the recovery of low
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amounts of organism (grows fast 6-8hrs.)
Serology tests for O1 can be screened for by using a commercially available
polyvalent O1 antiserum
Lab Diagnosis-Biochemical Tests
• Vibrio sp. are motile (polar flagellae)
• Oxidase +
• Nitrate +
• On TCBS media Yellow Colonies (2-4mm in diameter)
with transparent periphery
• On TTGA media dark centers surrounded by cloudy zone
of gelatinase activity
• Alkaline Peptone Broth-enhances recovery
when only a few organisms. Grows rapidly
• Can be inoculated with liquid stool, fecal
suspension or rectal swab
• String test + (Sodium deoxycholate)
“string of pearls”
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KIA K/A, no gas produced (red slant/yellow butt)
TSI A/A, no gas produced (yellow slant/yellow butt)
LIA K/K, no gas produced (purple slant/purple butt)
Wet mount---Small, curved rods with darting motility
Treatment
• Prompt treatment with fluid and electrolyte replacement before the
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resultant massive fluid loss
Antibiotics can reduce exotoxin production– rapidly eliminating
organism
Doxycycline or Tetracycline is the drug of choice in adults
Furazolidone is the drug of choice for pregnant women
SXT is drug of choice for children
Reported resistance to Tetracycline and SXT (Africa and Asia)
Also susceptible to gentamicin and chloramphenicol
Can grow on Mueller-Hinton—Standard disk diffusion (Kirby-Bauer)
for antimicrobial susceptibility
Prevention and Control
• O1 strain has 2 oral vaccines (whole killed cell)
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and a genetically engineered attenuated (live
attenuated) V. Cholerae vaccine
Improvement in sanitation (sewage
management, water purification, food
contamination)
Boiling shellfish >10 minutes destroys Vibrio
rendering it nonviable
References
• “Isolation and Identification of Vibrio Cholerae”
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http://www.cdc.gov/ncidod/diseaseinfo/cholera
Mahon, Connie, et. al. Diagnostic Microbiology. St. Louis: Sanders,
2007
Murray, Patrick, et. al. Medical Microbiology. St. Louis: Mosby
Publishing, 2002
Two cases of Toxigenic Vibrio cholerae O1 Infection After Hurricane
Katrina and Rita. Emerging Infectious Disease Journal. January 20
2006.
http://staff.vbi.vt.edu/pathport/pathinfo/pathogens/V_cholera.html