Shigella dysenteriae is a gram-negative, non-motile bacillus that causes dysentery. It grows well at 37°C in nutrient broth, forming colorless colonies on MacConkey agar and red colonies without black centers on XLD agar. S. dysenteriae infection is caused by ingesting contaminated food or water and leads to dysentery characterized by bloody mucus in stool. Laboratory diagnosis involves examining stool samples microscopically for pus cells and macrophages, culturing on selective media to isolate non-lactose fermenting colonies, and conducting biochemical tests and slide agglutination with specific antisera. Tetracycline and chloramphenicol are used

1. SHIGELLA
DYSENTERIAE
RATHEESH R.L

3. MORPHOLOGY
 An enterobacteriaceae
 Gram negative bacilli.
 Mostly non-motile
 Non sporing
 Size varies from 2-4um x 0.4 -0.6um

4. CULTURAL
CHARACTERISTICS
 They are aerobics and facultative
anaerobics
 Growing well in the temperature of 37
degree C and in the pH of 7.4.

5. NUTRIENT BROTH
 They produce mild turbidity after 24
hours of incubation.

6. NUTRIENT AGAR OR BLOOD
AGAR MEDIUM
 Circular, smooth grayish or colorless
Colonies will be formed after overnight
incubation.
 Size of the colonies will be 2-3mm

7. MACCONKEY AGAR MEDIUM
 They produce colorless colonies in the
medium

8. XLD(xylose lysine deoxycholate)
AGAR MEDIUM
 It is a selective medium and the
colonies formed are red color without
black centers.

9. DEOXYCHOLATE CITRATE
AGAR MEDIUM
 It is a selective medium for shigella
dysenteriae
 Small colorless colonies will be formed
in this medium.

10. PATHOGENESIS
 The species of this genus causes a serious
illness known as dysentery/shigellosis, which
is an acute diarrheal disease characterized by
passage of pus, blood or mucous through the
stool.
 Infection mainly occurs because of the
ingestion of contaminated food or water.

11.  Incubation period is 12-48 hours but may
vary between 1-7 days.
 Through the ingestion the bacilli will
reaches to the large intestine of the
humans.
 The multiplication occurs in the epithelial
cells of the large intestine.

12.  Then the bacteria spreads to adjacent
cells and to the lamina propria (is a
thin layer of loose connective tissue
which lies beneath the epithelium)
where the colonization occurs.

13.  After the growth and multiplication, it
starts to produce toxins.
 The lamina propria and sub mucosa
develops an acute inflammatory reaction
with formation of abscess on the
mucosal surface along with capillary
thrombosis by the production of toxins.

14.  The necrosed epithelium become soft
and sloughed out and causing
superficial ulcers and bleeding.
 The toxin produced by the shigella
bacteria have both enterotoxic effect
and neurotoxic effect.

15.  Thus their combined action leads to
severe diarrhea,poly neuritis, coma
and meningitis.

16. LABORATORY DIAGNOSIS
 Hematological investigations
 Bacteriological investigations
◦ Microscopic studies
◦ Culture studies
◦ Biochemical tests
◦ Slide agglutination test

17. Hematological investigations
 There will not be any significant
changes in the blood values.

18. Microscopic studies
 Under the microscope the wet
preparation of specimen shows large
number of pus cells with degenerated
nuclei, macrophages and RBC.

19. CULTURE STUDIES
 Feces or mucous specimens are
selected for the microscopic studies.
 After 12-18 hours of incubation non
lactose fermenting colonies will be
formed in the macconkey medium.

20. Biochemical tests
 H2S test: negative
 Citrate utilization test: negative
 Iodole test: positive
 M.R test: positive
 Urease test: negative
 Motility test: negative

21. Slide agglutination test
 It is performed with specific antisera
against the shigella dysenteriae.
 We can isolate the bacilli by adding
the antisera over the specimen.

22. TREATMENT
 Tetracycline and chloramphenicol is
the drug of choice against the shigella
dysenteriae.
 The treatment should be continued for
5-7 days.