HEKTOEN ENTERIC AGAR - 500 GRAMAS

Código: TM121 - Referência: HEKTOEN

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Composition

 

Ingredients

Gms/Ltr.

Agar

15.00

Lactose

12.00

Proteose peptone

12.00

Sucrose

12.00

Bile salts

9.00

Sodium chloride

5.00

Sodium thiosulphate

5.00

Yeast extract

3.00

Salicin

2.00

Ferric ammonium citrate

1.50

Acid fuschin

0.10

Bromo thymol blue

0.065

 * 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 76.6gms in 100ml distilled water. Gently heat to boiling with gentle swirling and dissolve the medium completely . DO NOT AUTOCLAVE OR OVERHEAT . Cool to 45- 50°C & use immediately.

 

Appearance: Light to dark green colour, trace to slightly hazy solution

pH: 7.5 ± 0.2

 

Principle

HEKTOEN ENTERIC AGAR is formulated by King and Metzger to isolate Shigella and Salmonella species. The medium contains Bile salt which is inhibitory to Gram -positive bacteria and many Gram - negative bacteria. The medium contains P roteose peptone as an essential amino acid and nitrogen supplement. Yeast extract is added as the source of vitamins and other growth factors. Sodium chloride helps maintaining the osmotic balance of the cells in the medium. Lactose present in the medium make                             s helps to differentiate lactose f ermenters from non - lactose fer menter s like Salmonella and late -lactose fermenters like Shigella. The medium cont ains other carbon sources like Sucrose and S alicin for optimal differentiation of enteric pathogens based on their ability to ferment different sugars. Acid fuschi                              n and Bromo thymo l blue acts as a pH indicator in the medium. E. coli is partially inhibited wherein they grow to a  limited  extent utilizing all           the three sugars like lactose, Sucrose and S alicin; forming salmon or orange coloured colonies in the medium. Sodium thiosulphat e and Ferric ammonium citrate helps in differentiation of H 2S producing coliforms. The H 2S producing coliforms like Proteus and Salmonella grow in the medium forming clear colony with a black center. Agar is added in the medium as a solidifying agent.

 

 Interpretation

Cultural characteristics observed after inoculating (103 - 105CFU/ ml ), on incubat ion at 35 ± 20C for 18 - 24 hours.

 

Microo rganisms

ATCC

Inoculum

(CFU/ml)

Recovery

rate (%)

Appearance of colon y

Escherichia coli

25922

103 - 105

Not limited

Orange colour colony with bile ppt., partially

inhibited

Enterococcus faecalis

29212

103 - 105

= 0.01%

Partially inhibited

Salmonella typhimurium

14028

103 - 105

= 20%

Black centered colony

Shigella flexneri

12022

103 - 105

= 5%

Greenish blue colour colony

 

References

  1. King and Metzger. Abstr. M 99, p. 77. Bacteriol. Proc. Am. Soc. Microbiol. (1967).
  2. King and Metzger. Appl. Microbiol . 16:577. (1968).
  3. King and Metzger. Appl. Microbiol. 16:579. (1968).
    1. MacFaddin. Media for isolation -cultivation -identification -maintenance of medical bacteria, vol. l. Williams & Wilkins, Baltimore, Md. (1985).
    2. Chapin and Murray . In Murray, Baron, Pfaller, Tenover and Yolken (ed.), Manual of clinical microbiology, 7th ed. American Society for Microbiology, Washington, D.C.                        (1999).

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