CRITERION™ HEKTOEN ENTERIC (HE) AGAR

Cat. no. C5840 CRITERION™ Hektoen Enteric Agar 152gm
Cat. no. C5841 CRITERION™ Hektoen Enteric Agar 500gm
Cat. no. C5842 CRITERION™ Hektoen Enteric Agar 2kg
Cat. no. C5843 CRITERION™ Hektoen Enteric Agar 10kg
Cat. no. C5844 CRITERION™ Hektoen Enteric Agar 50kg

INTENDED USE

Hardy Diagnostics CRITERION™ Hektoen Enteric (HE) Agar is a selective and differential medium used for the isolation and differentiation of gram-negative enteric bacilli.

This dehydrated culture medium is a raw material intended to be used in the making of prepared media products, which will require further processing, additional ingredients, or supplements.

SUMMARY

King and Metzger developed HE Agar in an effort to increase the recovery of Salmonella and Shigella species over the previously formulated Salmonella-Shigella (SS) Agar.(6) This medium is particularly useful in the isolation of Shigella species.

The present formulation of HE Agar incorporates larger amounts of peptone in order to offset the inhibitory effect of bile salts. Also, sodium deoxycholate has been eliminated and the amount of bile salts reduced. Bile salts allow for the selective nature of HE Agar by inhibiting gram-positive organisms. Bile salts can also be toxic for some gram-negative strains. Salicin, sucrose, and lactose are the fermentable carbohydrates present. They provide optimal differentiation of enteric pathogens. Lactose and sucrose, in increased concentration, aid in the differentation of slow lactose-fermenters. Bromothymol blue and acid fuchsin (Andrade's) are added as acid-base indicators. The addition of ferric ammonium citrate and sodium thiosulfate enable the detection of H2S, noted by the production of black centered colonies. Sodium thiosulfate serves as the sulfur source while ferric ammonium citrate serves as the indicator.

HE Agar is currently recommended as one of several plating media for the culture of Enterobacteriaceae from stool specimens. This is due to its moderately selective nature as well as for its differentiation properties.

FORMULA

Gram weight per liter: 76.0gm/L
Agar 14.0gm
Peptic Digest of Animal Tissue 12.0gm
Lactose 12.0gm
Sucrose 12.0gm
Bile Salts 9.0gm
Sodium Chloride 5.0gm
Sodium Thiosulfate 5.0gm
Yeast Extract 3.0gm
Salicin 2.0gm
Ferric Ammonium Citrate 1.5gm
Acid Fuchsin 0.1gm
Bromothymol Blue 0.064gm

Final pH 7.5 +/- 0.2 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.

STORAGE AND SHELF LIFE

Store the sealed bottle(s) containing dehydrated culture medium at 2-30ºC. Dehydrated culture medium is very hygroscopic. Keep lid tightly sealed. Protect dehydrated culture media from moisture and light. The dehydrated culture media should be discarded if it is not free-flowing or if the color has changed from its original light tan-green.

Store the prepared culture media at 2-8ºC.

PRECAUTIONS

METHOD OF PREPARATION FOR DEHYDRATED CULTURE MEDIA

1. Suspend 76.0gm of the dehydrated culture media in 1 liter of distilled or deionized water.

2. Heat to boiling and mix to dissolve completely. Do not overheat.

3. Do not autoclave.

4. Cool to 45-50ºC. and aseptically add enrichments, if desired.

PROCEDURE AND INTERPRETATION OF RESULTS

For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. G63.

LIMITATIONS

Cultural growth may be delayed or inhibited by the presence of antimicrobial agents in the specimen. Additionally, antimicrobics may alter the characteristic appearance of the organism on the medium.

It is recommended that selective enrichment broths (GN or Selenite Cystine) be used in conjunction with selective plating media for optimal isolation of enteric pathogens.

The bile salts may crystallize over time. They appear as small spider-like puff-balls within the medium and do not affect the performance of the medium.

Colonies of Proteus, which may or may not be inhibited, may resemble Salmonella or Shigella.

The recovery of most Shigella and many Salmonella spp. from unpreserved stool specimens may be jeopardized if processing delays exceed 2-3 hours.

MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as autoclave, incinerators, and incubators, etc., are not provided.

QUALITY CONTROL

Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Salmonella enterica
ATCC ® 14028
A 18-24hr 35°C Aerobic Growth; blue to blue-green colonies with black centers
Shigella flexneri
ATCC ® 12022
A 18-24hr 35°C Aerobic Growth; green to blue-green colonies
Enterococcus faecalis
ATCC ® 29212
B 18-24hr 35°C Aerobic Inhibition; may be slight growth of yellow colonies
Escherichia coli
ATCC ® 25922
B 18-24hr 35°C Aerobic Partial inhibition; may be slight growth of yellow to salmon colored colonies

User Quality Control

PHYSICAL APPEARANCE

CRITERION™ Hektoen Enteric (HE) Agar powder is homogeneous, free-flowing, and dark green in color. The prepared media should appear clear, and green in color.

REFERENCES

1. Versalovic, J., et al. Manual of Clinical Microbiology. American Society for Microbiology, Washington, D.C.

2. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.

3. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.

4. MacFaddin, J.F. 1985. Media for Isolation, Cultivation, Identification, Maintenance of Bacteria, Vol. I. Williams & Wilkins, Baltimore, MD.

5. Quality Assurance for Commercially Prepared Microbiological Culture Media, M22. Clinical and Laboratory Standards Institute (CLSI - formerly NCCLS), Wayne, PA.

6. King, S. and Metzger, W.I. 1968. Applied Microbiology; 16:577-579.


ATCC is a registered trademark of the American Type Culture Collection.

053116gr