MORPHOLOGY AND CULTURE CHARACTERISTICS OF SHIGELLA DYSENTERIAE (SH. DYSENTERIAE)

MORPHOLOGY OF SHIGELLA DYSENTERIAE (Sh. dysenteriae)

ShapeShigella dysenteriae is a short, rod shape (bacillus) bacterium.

Size – The size of Shigella dysenteriae is about 1–3 µm × 0.5 µm (micrometer).

Arrangement Of CellsShigella dysenteriae is arranged singly or in pairs.



MotilityShigella dysenteriae is a non-motile bacterium. Some strains of E. coli are non-motile.

FlagellaShigella dysenteriae is a non-flagellated bacterium.

Spores – The Shigella dysenteriae is a non–sporing bacterium.

CapsuleSh. dysenteriae is a Non-capsulated bacterium.

Gram Staining Reaction – Shigella dysenteriae is a Gram -ve (Negative) bacterium.

morphology of shigella dysenteriae - size of shigella dysenteriae - shape of shigella dysenteriae
MORPHOLOGY OF SHIGELLA DYSENTERIAE

CULTURE REQUIREMENTS OF SHIGELLA DYSENTERIAE (Sh. dysenteriae)

Special requirementsShigella dysenteriae have no complex nutritional requirements and readily grow in ordinary media like Nutrient Agar medium (NAM). Commonly the MacConkey Agar medium & XLD medium is used for the cultivation of Shigella dysenteriae in the Laboratory.

 Optimum temperatureShigella dysenteriae ranges from 10–40°C but the optimum temperature for most of the strains is 37°C and usually cultivated at this temperature in laboratories.

⇒ Optimum pHSh. dysenteriae cannot survive at acidic pH below 4.5, the maximum growth observed at 7.0 i.e. neutral pH. Also, the pH requirement varies as per the strain of Escherichia col.

⇒ Oxygen requirementsShigella dysenteriae (Sh. dysenteriae) is an aerobic bacterium i.e. grow best in the presence of oxygen and it is also a Facultative anaerobic organism i.e. can grow in a low oxygen environment.

⇒ There are various culture media used for the cultivation of Shigella dysenteriae (Sh. dysenteriae) in the laboratory and most commonly the MacConkey Agar medium, XLD medium and Selenite F broth medium is used which may vary as per the SOPs of the laboratory, the other media are as follows –

  • Columbia Horse Blood Agar medium.
  • Sheep Blood Agar medium.
  • Eosin Methylene blue Agar (EMB) medium
  • Deoxycholate Citrate Agar (DCA) medium (Selective medium for Salmonella & Shigella).
  • Salmonella – Shigella Agar medium (Selective medium for Salmonella & Shigella).
  • Xylose Lysine Deoxycholate (XLD) medium (Selective medium for Salmonella & Shigella).
  • Selenite F Broth (Selective medium for Salmonella & Shigella).
  • The Liquid medium (Trypticase Soy Broth, Nutrient broth, etc.)

Check out the Morphology & Culture Characteristics of Salmonella typhi

MORPHOLOGY AND CULTURE CHARACTERISTICS OF SALMONELLA TYPHI (S. TYPHI)

 The Deoxycholate Citrate Agar (DCA) medium is the Selective medium for Shigella dysenteriae & other Shigella Species as well as Salmonella Spp. contains Deoxycholate and Citrate salts in a concentration that inhibits the growth of many gram-positive bacteria & most of the intestinal flora and supports the growth of Shigella dysenteriae.

 Similarly, the Salmonella – Shigella Agar medium is also a selective medium for Shigella dysenteriae & other species of Shigella as well as Salmonella spp. contains 4 key components that make it selective for Salmonella & Shigella i.e. Bile salts, Brilliant green dye, Sodium citrate & Sodium thiosulfate which selectively inhibit the growth of many gram-positive bacteria & coliform bacteria and supports the growth of Salmonella & Shigella sp.



CULTURE CHARACTERISTICS OF SHIGELLA DYSENTERIAE (Sh. dysenteriae)

Cultural CharacteristicsNutrient Agar Medium (NAM)MacConkey Agar mediumBlood Agar MediumXylose Lysine Deoxycholate Agar (XLD) Medium
ShapeCircularCircularCircularCircular
Size1-2 mm1-2 mm1-3 mm2-3 mm
ElevationConvexConvexConvexConvex
SurfaceSmoothSmoothSmoothSmooth
ColorGreyish whiteColorlessGreyish whiteRed without black center
StructureTranslucentTransparentTranslucentTranslucent –Opaque
Hemolysis----------γ-Hemolysis (Non - Hemolytic)-----

Check out the preparation of MacConkey Agar medium in Laboratory

PREPARATION OF MACCONKEY AGAR MEDIUM (MAC) IN LABORATORY

In liquid culture media like Trypticase soy broth or Nutrient broth, the growth of the bacterium occurs as turbidity in the broth medium but the chances of contamination are high especially when the isolation is carried out from Feces specimen, commonly the Selenite F broth and Tetrathionate broth is used for the isolation of Shigella dysenteriae.

In Blood Agar medium, the Shigella dysenteriae shows gamma hemolysis i.e. no hemolysis occurs on blood agar medium, the colonies are grayish-white and grows well.

shigella dysenteriae on blood agar medium - Sh. dysenteriae on blood agar
CULTURE OF SHIGELLA DYSENTERIAE ON BLOOD AGAR MEDIUM

In MacConkey Agar medium, the colonies of Shigella dysenteriae are colorless due to the lack of lactose fermentation which is of great importance in differentiating Sh. dysenteriae from other Bacteria present in the specimen, especially from Gram-positive bacteria and Escherichia coli which is lactose fermentor and gives Pink color colonies on MacConkey agar medium.

In Eosin Methylene Blue Agar (EMB) medium, the colonies of Shigella dysenteriae are colorless due to lack of lactose fermentation.

In the Deoxycholate Citrate Agar medium, the colonies of Shigella dysenteriae are colorless due to Non-Lactose Fermentation (NLF).

In Salmonella Shigella Agar medium, the colonies of Shigella dysenteriae are Colorless. Hydrogen sulfide is not produced by Shigella dysenteriae.

shigella dysenteriae on salmonella shigella agar medium
CULTURE OF SHIGELLA DYSENTERIAE ON SALMONELLA SHIGELLA AGAR MEDIUM (COLORLESS COLONIES)

Selenite F broth, the enrichment medium for Shigella & Salmonella species, commonly used for the isolation of the organism from the fecal sample where the density of Shigella dysenteriae may be too low in early stages of infection. The fecal specimen inoculated in Selenite F broth are incubated for 6-12 hours generally (not more than 24 hours) and then subcultured on XLD medium or any other selective medium.

shigella dysenteriae on xylose lysine dextrose agar - shigella dysenteriae on xld medium
CULTURE OF SHIGELLA DYSENTERIAE ON XLD MEDIUM

That’s all about the Morphology and Culture Characteristics of Shigella dysenteriae



Further Reading:

Wikipedia

Microbeonline

Microbewiki

University of Copenhagen

food.unl

2 thoughts on “MORPHOLOGY AND CULTURE CHARACTERISTICS OF SHIGELLA DYSENTERIAE (SH. DYSENTERIAE)

Leave a Reply

Your email address will not be published. Required fields are marked *