Gram Negative Curved Bacilli
There are certain microorganisms that share this type
of morphology which is sometimes is described as
comma-shaped. The following m.o. are curved gram negative bacilli:
1. Vibrio.
2. Aeromonas.
3. Plesiomonas.
4. Campylobacter.
5. Helicobacter
They are :
A. Gram negative curved bacilli.
B. Motile by a single polar flagellum.
C. Some of these m.o. can cause diarrhoea in humans.
Genus : Vibrio
1. Vibrio cholerae : Causes epidemic and pandemic cholera.
2. Non-cholera Vibrios: Cause ear, wound, soft tissue, and extra-intestinal infections.
3. Vibrio parahaemolyticus: Causes gastroenteritis, and possibly extra-intestinal infections.
Vibrio cholerae:
Serolgy:
have 2 important antigens; H (shared), and O
(specific)
Vibrio cholerae of O group 1 (o1) and 139
(O139) cause the classical disease cholera,
while the non-O1/ non-O139 V. cholerae
cause cholera-like disease.
Both O1 and O 139 V.cholerae can be of two
biotypes:
1. Classical
2. El-Tor
Then both biotypes can be subgrouped into
serotypes
according to 3 antigenic factors (A, B, and C)
:
Ogawa (A,B), Inaba (A,C), and Hikojima
(A,B.C).
Moroholgy :
These m.o. are highly aerobic, very actively
motile (described as shooting stars or
darting motility)
Biochemiacl activity :
1. These m.o. are respiratory (oxidase
positive) and fermentative (catalase
positive).
2. They give positive cholera-red reaction on
nitrate peptone
3. The TSI shows A/A profile (yellow
colour).
4. The optimum pH for the growth of these
m.o. is 7.0, but they can tolerate up to 8.5
- 9.0.
5. They are very sensitive to acidic pH (less
than 6), therefore, they are quite
susceptible to gastric juice (a major
barrier against V.cholers )
Culture of V. cholerae:
This m.o. can be cultivated on different
media:
1. Alkaline Peptone Water (APW; Sea Water):
This medium is of pH 8.5 – 9.0 and used for
the primary (first) isolation from clinical
specimens. Many m.o. can not tolerate such
pH, but Pseudomonas does.
2. Thiosulfate Citrate Bile Salt Sucrose Agar
(TCBS):
3. Tellurite Taurocholate Gelatin Agar (TTGA):
4. Meat Extract Agar: .
5. Taurocholate Pepton Broth:
6. MacConkey’s Agar:
V.Cholerae colonies are of non-lactose
fermenters.
7. Blood Agar:
El-Tor growth shows beta-haemolysis ( vesus
the classical).
Practical procedure of cultivation of V.
cholerae:.
1. Direct stool examination:
a. Motility.
B. Microscopical exam.: mucous, epith.
cells, and large numbers of m.o., but no pus
cells are seen.
c. Fluorescent antibody staining.
2. 2 ml of faeces + 20 ml APW pH 8.0 – 8.5
are incubated for 5 hours.
3. From the APW, TCBS and another APW .
4. The colonies are subjected to further
identification (see it to right )
Further Identification of V. cholerae:
1. String test:
If positive, it means V. cholerae.
2. Polyvalent anti-sera (anti-O1, anti- O139):
To confirm that the V. cholerae belongs to
O-1 or O-139
3. Biochemical tests including cholera red
reaction.
4. Differentiation between classical & El-Tor
Biotypes:
5. Serotyping: by specific antisera against A,
B and A antigenic factors to determine
Ogawa, Inaba & Hikojima.
Cholera:
1. Cholera is an acute infectious disease
characterized by
2. severe vomiting and watery diarrhoea
(rice water stool)
3. resulting in dehydration and collapse.
4. Infection occurs by oral route through
contaminated food or drink .
5. Source of infection is a case or a carrier
who excretes the organism in the stool.
6. The organisms attach to the microvilli of
the brush border of epithelial cells, where
they multiply and liberate cholera
enterotoxin which exerts the above
mentioned effects.
7. The stool contains mucous, epith. cells,
large numbers of m.o. and no pus cells.
Finally, mortality from untreated cholera may
reach up to 25% - 50%
Factors of Pathogenicity of V. cholerae:
1. Adherance and Motility:
The actively motile m.o. can adhere to the
intestinal wall (pathogenic), and vice versa
for the non-motile (non-pathogenic).
V.cholerae does not usually reach to the
blood stream.
2. Enterotoxin:
Has tow portion
a. Toxic portion (A1)
b. Stabilizer portion (A2).
The A1 portion increases the intracellular
cAMP of the intestinal epithelium. The cAMP
prevents reabsorption of Na (1 X), excretion
of NaHCO3 (2 X),chloride and K (3-5 X). This
leads to accumulation of water in large
quantities (> 20 liters/day), acidosis,
hypokalaemia, and death.
Diagnosis of cholera:
A. First case in non-endemic
area:
Any comma-shaped motile
m.o. detected in a stool
positive for cholera
B. Second case during an
epidemic:
cases can be diagnosed by:
1. direct stool examination
mainly for motility,
2. and immobilization by
specific anti-O antisera.
3. PCR assays have been
developed for detection of
cholera toxin genes.
Treatment and control of
cholera:
1. Intravenous fluid and
electrolytes replacement:
This is the most important
part of the therapy.
2. Oral anti-microbial drugs:
Have a secondary role in the
treatment. Tetracyclines are
the most effective drugs.
3. Control: The main control
measures are:
a. Community and
personal hygiene.
b. Isolation of cases and
proper disposal of sewage.
c. Chemoprophylaxis by
using tetracyclines for
exposed persons.
d. Immunoprophylaxis
Immunity against cholera:
The immunity against cholera
could be achieved by:
1. Gastric juice: It is a major
barrier against infection by V.
cholerae.
2. Secretory IgA: Intestinal
secretory IgA prevents the
attachment of m.o. to the
intestinal wall.
3. Vibriocidal IgG: Anti-toxic
Ab, presents in the serum.
4. Solid immunity can stay for
3 years after infection.
5. Immunoprophylaxis:
a. Heat killed vaccine:
Given in 2 subcutaneous
doses. It stimulate
anti-bacterial and not
anti-toxic antibodies.
b. Live oral vaccine:
Protects against cholera
enterotoxin
c. O-139
.
