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Material Safety Data Sheet

Organisms

Organisms this product works with:

For this Organism

Other products used in the isolation of Salmonellae:

Dehydrated Culture Media

HEKTOEN ENTERIC AGAR

Code: CM0419

A differential, selective medium for the isolation of Shigella and Salmonella species from enteric pathological specimens.

Typical Formula*

gm/litre

Proteose peptone

12.0

Yeast extract

3.0

Lactose

12.0

Sucrose

12.0

Salicin

2.0

Bile salts No.3

9.0

Sodium chloride

5.0

Sodium thiosulphate

5.0

Ammonium ferric citrate

1.5

Acid fuchsin

0.1

Bromothymol blue

0.065

Agar

14.0

pH 7.5 + 0.2 @ 25°C

* Adjusted as required to meet performance standards 

Directions
Suspend 76g of the medium in 1 litre of distilled water and soak for 10 minutes. Heat gently and allow to boil for a few seconds to dissolve the agar. DO NOT AUTOCLAVE. Cool to 50°C and pour plates.

Description
Hektoen Enteric Agar was developed by King & Metzger1. The high peptone content offsets the inhibitory effect of bile salts on Shigella species in particular. The additional carbohydrates (sucrose and salicin) give better differentiation than lactose alone and the lower toxicity of the double indicator improves recovery. The increased lactose content helps early recognition of slow lactose-fermenting organisms. The thiosulphate and ferric citrate are present to detect H2S-producing organisms.

Taylor & Schelhaut2 found the medium to be of value in the differentiation of pathogenic organisms and for better growth of shigellae.
Hoben et al.3 added novobiocin 15 mg/litre to improve the selectivity of the medium by inhibiting Citrobacter and Proteus species.
Hektoen Enteric Agar meets the requirements of the APHA4.

Technique
Inoculate the medium with fresh faeces suspended in Ringers solution or inoculate directly with rectal swabs. Spread the inoculum to obtain well separated colonies. Incubate for 18-24 hours at 37°C. Further incubation will improve differentiation between shigellae and salmonellae.

Organism characteristics:

Shigella

Green, moist raised colonies

Salmonella

Blue-green colonies with or without black centres

Coliforms (rapid lactose/sucrose/salicin fermenters)

Salmon-pink to orange colonies surrounded by a zone of bile precipitation

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared plates at 2-8°C.

Appearance
Dehydrated medium: Pale green coloured, free-flowing powder
Prepared medium: Green to dark green coloured gel

Quality control

Positive controls:

Expected results

Salmonella typhimurium ATCC® 14028 *

Good growth; blue-green coloured colonies with black centres

Shigella flexneri ATCC® 12022 *

Good growth; green coloured colonies

Negative controls:

 

Escherichia coli ATCC® 25922 *

Inhibited or no growth

Enterococcus faecalis ATCC® 29212 *No growth
* This organism is available as a Culti-Loop®

Precautions
Do not overheat the medium or hold it molten for long periods. Proteus species may resemble salmonellae or shigellae.
Further testing must be carried out to confirm the presumptive identification of organisms isolated on this medium.

References
1. King S. and Metzger W. I. (1968) Appl. Microbiol. 16. 577-561.
2. Taylor W. I. and Schelhaut D. (1971) Appl. Microbiol. 21. 32-37.
3. Hoben D. A., Ashton D. H. A. and Peterson A. C. (1973) Appl. Microbiol. 21. 126-129.
4. American Public Health Association (1992) Compendium of Methods for the Microbiological Examination of Foods 3rd Edition. APHA Inc. Washington DC.

 
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