⇒ Special requirements – Shigella 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.
What is the purpose of DCA agar?
Deoxycholate Citrate Agar is used for the isolation and differentiation of Gram-negative enteric bacilli in a laboratory setting. It is particularly useful for the isolation of organisms that cause bacillary dysentery, Salmonella strains that cause food poisoning and Salmonella Paratyphi.
What grows on DCA agar?
Coliform bacteria and gram-positive bacteria are inhibited or greatly suppressed due to sodiumdeoxycholate, sodium citrate and ferric ammonium citrate….Composition of Deoxycholate Citrate Agar (DCA)
| Ingredients | Gm/litre |
|---|---|
| Sodium thiosulphate | 5.4 |
| Ferric ammonium citrate | 1.0 |
| Sodium deoxycholate | 5.0 |
| Neutral red | 0.02 |
What media does Shigella grow on?
Salmonella Shigella (SS) Agar is moderately selective and differential medium for the isolation, cultivation and differentiation of Salmonella spp. and some strains of Shigella spp. SS Agar is a modification of the Desoxycholate Citrate Agar.
What bacteria grows on Salmonella Shigella Agar?
Results
| Name of the organisms | Colony characteristics in Salmonella-Shigella agar |
|---|---|
| E.coli | Slight growth, pink or red |
| Enterobacter/Klebsiella | Slight growth, pink |
| Proteus | Colorless colonies, usually with black center |
| Salmonella | Colorless colonies, usually with black center |
Why is Salmonella Shigella Agar not autoclaved?
Preparation Instructions Suspend 63 grams of SS Agar in 1000 mls of distilled water. Boil with frequent agitation to dissolve the medium completely. Do not autoclave or overheat. Overheating may destroy the selectivity of the medium.
What is LF and NLF bacteria?
Pale (NLF) and pink (LF) colonies on MacConkey Agar. Colorless colonies/pale colonies (colonies similar to the color of the media): Colorless or pale colonies indicate that the test organism is a non-lactose fermenter. Examples include species of Salmonella, Shigella, Proteus, Providencia, Pseudomonas, Morganella, etc.
How do you test for Shigella?
To confirm the diagnosis of shigellosis, doctors take a sample of stool and send it to a laboratory to grow (culture) and identify the bacteria. Bacteria are also tested to see which antibiotics are effective (a process called susceptibility testing.
What makes Salmonella Shigella Agar selective?
Limitations of SS Agar The incorporation of brilliant green into this medium makes it highly selective, and has been shown to inhibit the growth of some Shigella. The bile salts may crystallize over time.
What are the major components of Salmonella Shigella Agar?
Salmonella Shigella agar comprises of bile salts, sodium citrate, brilliant green, enzymatic digest of casein, beef extract, enzymatic digest of animal tissue, thiosulphate, ferric citrate, neutral red and agar.
Does Shigella dysenteriae show hemolysis in blood agar medium?
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.
What is the best media for the isolation of Shigella dysenteriae?
⇒ 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.
Is hydrogen sulfide produced by Shigella dysenteriae on Salmonella agar?
In Salmonella Shigella Agar medium, the colonies of Shigella dysenteriae are Colorless. Hydrogen sulfide is not produced by Shigella dysenteriae.
How do you identify Salmonella on DCA?
Suspected pathogens must be subcultured on a less inhibitory medium prior to identification. As there are many bacteria that also look like Salmonella on DCA, it is widely recommended that more selective agars are used for the identification of Salmonella, namely xylose lysine deoxycholate (XLD) agar.
