|Several students of a primary
school in a village fell ill. All of
them were admitted to local hospital following vomiting and
diarrhea. Purging was effortless and the feces was non-odorant and
What is your diagnosis?
It is a case of gastoenteritis, probably cholera.
Which are the pathogens that can cause gastroenteritis?
Common bacteria that can cause gastroenteritis include vibrio
cholerae and Enterotoxigenic E.coli (ETEC).
What is the pathogenesis of cholera?
Cholera is basically an enteric disease and the
transmission involves feco-oral route. Vibio cholerae is
transmitted following ingestion of contaminated food or water. Ingestion of
large numbers of
bacilli (approximately 106) can initiate infection in a
susceptible person. Once they survive the gastric juices, they
reach small intestine and colonize the epithelial lining and
produce cholera toxin. They adhere to the intestinal wall mediated
by toxin-coregulated pilus (TCP). Hemagglutinin/protease is a
zinc-dependent protease, which cleaves the mucin
and fibronectin and may serve to facilitate the spread and
excretion of vibrios within the intestine in stools by detaching
them from the intestinal walls. Incubation period can be short (1-3 days).
Cholera toxin is holotoxin consisting of A subunit and B subunit.
The B subunit binds to specific ganglioside receptors (GM1) on the
epithelial cells of small intestine and facilitates the entry of A
subunit where it activates adenylate cyclase. Stimulation of
adenylate cyclase causes an increased production of cAMP, which
leads to hypersecretion of water and electrolytes into the lumen
and inhibition of sodium reasborption.
What is the specimen collected and how is the condition
diagnosed with the aid of laboratory?
Freshly passed feces is collected in a sterile wide mouthed
container, if no feces is available rectal swabs may also be
taken. In case
of delay, the feces may be transported in transport medium such as
Cary Blair medium or VR medium. The enrichment medium alkaline
peptone water may also be used as transport medium. Direct gram stained smear
hanging drop preparation may be useful. Feces is inoculated on to MacConkey's agar, and on to selective media such as
Agar and incubated at 37oC overnight. The sample may
also be inoculated into enrichment broth such as
alkaline peptone water and subcultured after 6 hours of
incubation on to MacConkey's agar for subsequent
What is your observation?
Hanging drop preparation
or darkground microscopy shows actively motile (darting-type)
bacilli. Vibrio can be detected by immobilization test, wherein
addition of vibrio antisera renders the bacilli in feces
non-motile. Gram stain of mucus flakes in feces shows several
curved, gram negative bacilli.
(non-lactose fermenting), smooth, low convex, circular colonies is seen on
On further incubation, colonies turned pink due to late lactose
fermentation. TCBS agar shows yellow coloured colonies. Surface pellicle is
noticed in alkaline peptone water. Gram stained smear of the
colony shows curved gram negative bacilli, hanging drop shows
actively motile bacilli, catalase test
and oxidase test
are positive. Results of biochemical
reactions are: positive
indole test, negative urea hydrolysis, positive
citrate utilization, positive MR test and negative VP
test. TSI agar shows
acid slant/acid butt with no gas or H2S.
ferments mannose and sucrose with acid production. Other tests
that help in identifying Vibrio are string test and nitrosoindole
test. The isolate is identified as Vibrio cholerae.
How do you identify the species?
Slide agglutination with antiserum against H antigen confirms that
it is a Vibrio sps. Further slide agglutination using O1 antiserum
is used to identify V. cholerae O1 from NAG vibrios. Serotyping by
slide agglutination is performed to identify Ogawa, Inaba or
Hikojima serotypes. Biotyping is undertaken by performing chick
RBC agglutination, Hemolysis, VP test, susceptibility to Polymyxin
B and Phage IV to differentiate ElTor from Classical biotype.
Is it necessary to identify the serotype and biotype?
Identity of the serotype and biotype is not important for
treatment. Serotyping and biotyping is only
Is antibiotic treatment necessary?
The mainstay of treatment is replacement of water and
electrolytic, restoration of acid-base balance; role of
antibiotics is secondary and serves to eradicate bacteria.
What are the complications of cholera?
Applied home Next
After dehydration, hypoglycemia is the most common lethal
complication of cholera in children. Acidosis in cholera is a
result of bicarbonate loss in stools and accumulation of lactate.
Acidemia occurs when respiratory compensation is unable to sustain
a normal blood pH. Hypokalemia results from potassium loss in the