DCLS Agar

Intended Use

DCLS Agar (Desoxycholate Citrate Lactose Sucrose Agar) is a moderately selective culture medium for the isolation of Salmonella and Shigella from fecal specimens.

Summary and Explanation

DCLS Agar is a modification of Leifson’s Desoxycholate Agar, a slightly selective and differential plating medium for enterics in which the degree of inhibition is accurately controlled by
the substitution of pure chemicals for the largely undefined composition of bile.¹ DCLS Agar is only one of a number of modified desoxycholate-containing media and differs from the
rest by its inclusion of sucrose.²
DCLS Agar supports good growth of cultures of Shigella and Salmonella, and inhibits the growth of coliforms and Proteus. In addition to the human pathogens, S. pullorum and S. gallinarum grow well.

Principles of the Procedure

This medium contains peptones and beef extract, which supply essential nutrients for the support of bacterial growth. The citrate and desoxycholate compounds serve as inhibitors of gram-positive bacteria and coliforms. The incorporation of two sugars permits the formation of red colonies by organisms that rapidly ferment either sucrose or lactose, or both; e.g., Proteus vulgaris, as well as typical coliforms. This permits the more accurate selection of members of the genera Shigella and Salmonella, which form colorless or nearly colorless colonies on DCLS Agar.

User Quality Control

Identity Specifications
DCLS Agar
Dehydrated Appearance: Fine, homogeneous powder.
Solution:                       5.0% solution, soluble in purified water upon
                                    boiling. Solution is medium to dark, red-orange
                                    to orange-rose, clear to slightly hazy.
Prepared Appearance:     Medium to dark, red-orange to orange-rose,
                                    clear to slightly hazy. 
Reaction of 5.0%
Solution at 25°C:            pH 7.2 ± 0.2
Cultural Response
BBL™ DCLS Agar
Prepare the medium per label directions. Inoculate and incubate at 35 ± 2°C for 24 hours.

Formula

DCLS Agar
Approximate Formula* Per Liter
Sodium Desoxycholate.................................................. 2.5 g
Sodium Citrate........................................................... 10.5 g
Lactose....................................................................... 5.0 g
Sucrose....................................................................... 5.0 g
Pancreatic Digest of Casein........................................... 3.5 g
Peptic Digest of Animal Tissue....................................... 3.5 g
Beef Extract................................................................. 3.0 g
Sodium Thiosulfate...................................................... 5.0 g
Neutral Red............................................................... 0.03 g
Agar......................................................................... 12.0 g
*Adjusted and/or supplemented as required to meet performance criteria.

Directions for Preparation from Dehydrated Product

1. Suspend 50 g of the powder in 1 L of purified water. Mix thoroughly.
2. Heat with frequent agitation and boil for 1 minute to completely dissolve the powder. Avoid excessive heating.
DO NOT AUTOCLAVE.
3. Cool the medium to approximately 45°C and pour into plates using about 20 mL per plate. The plates may be used at once or refrigerated for a few days.
4. Test samples of the finished product for performance using stable, typical control cultures.

Procedure

Inoculate and incubate plates, protected from light, at 35 ± 2°C for 18-24 hours. If negative after 24 hours, reincubate an additional 24 hours.
A nonselective medium should also be streaked to increase the chance of recovery when the population of gram-negative organisms is low and to provide an indication of other
organisms present in the specimen.

Expected Results

Typical colonial appearance on DCLS Agar is as follows:
Escherichia coli .......................... Large, flat, pink to rose red with a zone of precipitated bile salts
Enterobacter/Klebsiella............... Large, mucoid, pink
Proteus.......................................Colorless to red
Salmonella ................................. Colorless to pale pink
Shigella ...................................... Colorless to pale pink
Pseudomonas ............................. Colorless to brown or green
Gram-positive bacteria ................ No growth

*Store at 2-8°C.

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