SIMMON'S CITRATE AGAR - 500 GRAMAS

Código: TM006 - Referência: SIMMON'S

SOLICITE SEU ORÇAMENTO

COMPARTILHAR:

For differentiation of gram-negative bacteria on the basis of citrate utilization

Composition

 

Ingredients

Gms/Ltr.

Agar

15.00

Sodium chloride

5.00

Sodium citrate

2.00

Ammonium dihydrogen phosphate

1.00

Dipotassium phosphate

1.00

Magnesium sulphate

0.20

Bromthymol blue

0.08

* Dehydrated powder, hygroscopic in nature, store, in a dry place in tightly- sealed containers below 25°C and protect from direct Sunlight.

Instructions for use

Dissolve  24.28gms in 1000ml of distilled water. Gently heat to boiling with gentle  swirling and dissolve   the medium completely. Sterilize by autoclaving at 15psi (1210C) for 15 minutes. Cool to 50°C and pour in sterile Petri plates or into test tubes.

Appearance: Forest green colour, clear to slightly opalescent gel

pH: 6.9 ± 0.2

 

Principle

SIMMONS CITRATE AGAR is used for differentiation of gram-negative bacteria on the basis of citrate utilization. Citrate acts source of carbon and nitrogen in the medium. Ammonium dihydrogen phosphate provides nitrogen in the medium. Dipotassium phosphate acts as a buffer. Sodium chloride maintains the osmotic balance of the medium. Sodium citrate is the sole source of carbon in this medium. Magnesium sulphate is a cofactor for the metabolic process. Organisms that can utilize Ammonium dihydrogen phosphate and Sodium citrate as their sole sources of nitrogen and carbon will grow on this medium and produce a color change from green (neutral) to blue (alkaline). Agar is the solidifying agent. The alkaline reaction takes place when excess CO2 is generated (Kreb’s cycle) as citrate is cleaved to form oxaloacetate. Oxaloacetate is decarboxylated to pyruvic acid and CO2. The excess CO2 combines with sodium and water that is already present in the medium to form sodium carbonate. In addition, bacteria that utilize citrate can extract nitrogen from the ammonium phosphate present in the medium, forming ammonia which combines with water to form NH4OH. The formation of these end products produce an alkaline pH in the medium (greater than 7.6), resulting in a color change which is detected  by  Bromothymol blue. Colour change from green to blue is the indication of positive reaction.

 

Interpretation

Cultural characteristics observed after inoculating (103-105CFU/ml), on incubation at 350C for  24  -  48 hours.

 

Microorganisms

ATCC

*Inoculum

(CFU)

Growth

Citrate utilization, Medium

colour changes

Enterobacter aerogenes

13048

80

Luxuriant

Positive, blue colour

Salmonella enteritidis

13076

84

Luxuriant

Positive, blue colour

Salmonella typhimurium

14028

85

Luxuriant

Positive, blue colour

Salmonella typhi

6539

82

Fair - Good

Negative, green colour

Shigella dysenteriae

13313

≥ 1000

Inhibited

-----

Escherichia coli

25922

≥ 1000

Inhibited

-----

 

Reference

1. MacFaddin J., Media for Isolation-Cultivation-Identification-Maintenance of Medical Bacteria, Vol. 1, Williams and Wilkins, Baltimore. (1985).

2. Simmons, J. Infect. Dis., 39:209. (1926).


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