Stx Induction Broth

Cat. no. K274 Stx Induction Broth, 15x103mm Tube, 4ml 20 tubes/box


Hardy Diagnostics Stx Induction Broth is recommended as an enrichment method for the stimulation of Shiga toxin (Stx) production by Shiga toxin-producing Escherichia coli (STEC).


STEC strains make up a new group of pathogens causing hemorrhagic colitis and hemolytic uremic syndrome in humans.(1) STEC are spread from animal feces, which contaminate food, water, and the environment.(2) Strains have been isolated from pigs, cows, and contaminated foodstuffs of animal origin. Human infection occurs through, but is not limited to, contact with environment or ingestion of contaminated foodstuff and water.(2) The STEC group comprises E. coli strains of large serological diversity, and includes, but is not limited to, E. coli serotypes OR, ONT, O26, O45, O48, O103, O104, O111, O118, O145, and O157.(2,3) The two major toxins produced by STEC are Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2), which are genetically and immunologically different from each other.(3) Stx1 and Stx2 are also known as Verotoxin 1 (VT1) and Verotoxin 2 (VT2), respectively.

Stx Induction Broth is comprised of BHI broth, a general-purpose liquid medium, and a toxin inducing agent, which stimulates the production of Shiga toxins by E. coli. Hardy Diagnostics Stx Induction Broth has been shown to greatly enhance Shiga toxin production in STECs compared to standard BHI broth.(4)


Ingredients per liter of deionized water:*

Induction Broth:
Calf Brain-Beef Heart Infusion 17.5gm
Pancreatic Digestion of Gelatin 10.0gm
Sodium Chloride 5.0gm
Disodium Phosphate 2.5gm
Dextrose 2.0gm
Toxin Inducing Agent 1.0mg

Final pH 7.3 +/- 0.2 at 25ºC.

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


Storage: Upon receipt store at 2-8ºC. Media should not be used if there are any signs of deterioration, discoloration, contamination, or if the expiration date has passed. Product is temperature sensitive; protect from excessive heat and moisture.



Specimen Collection: Consult appropriate references to determine how to correctly collect the specimen to be tested (stool, food, etc.).(5-8) Infectious material should be submitted directly to the laboratory without delay and protected from excessive heat and cold. Specimens should be delivered to the laboratory within 2-3 hours. Special attention is required for stools; they should be collected early in the course of the disease and need to be cultured within two hours after collection. If there is to be a delay in processing, the specimen should be inoculated onto an appropriate culture transport medium (such as Cary-Blair, Cat. no. 280505) and refrigerated until tested.

Method of use: Inoculate broth using aseptic techniques. Swab specimens may be inserted directly into the broth. Medium should be incubated aerobically for 4-24 hours at 35 +/- 2ºC. before proceeding with toxin testing.


Stx Induction Broth is intended for the stimulation of Shiga toxin production prior to further toxin testing (such as immunoassays, PCR, or other quantitative or qualitative methods), therefore no results are interpreted directly from incubation in this medium.


If no visible growth is seen within 24 hours, the inoculated tube should not be used for toxin testing.


Standard microbiological supplies and equipment such as loops, other culture media, swabs, applicator sticks, incinerators, and incubators, etc., as well as materials for other toxin testing methods, are not provided.


Test Organism Inoculation Method* Incubation Results
Time Temperature Atmosphere
Escherichia coli (O157:H7)
ATCC ® 35150**
A 18-24hr 35°C Aerobic Growth; turbid
Escherichia coli (O157:H7)
ATCC ® 35150
I*** 18-24hr 35°C Aerobic Growth; pink to red colonies on MacConkey

**Recommended QC strain for User Quality Control according to the CLSI document M22 when applicable.

** *Stx Induction Broth is inoculated with a single colony, incubated for 4-6 hours, then subcultured to MacConkey Agar and incubated for 18-24 hours to ensure recovery.


Physical Appearance

Stx Induction Broth should appear clear and may have slight precipitate, and light amber in color.


1. Beutin, L., et al. 1989. Close Association of Verotoxin (Shiga-Like Toxin) Production with Enterohemolysin Production in Strains of Escherichia coli. J. Clin. Microb.; 27:2559-2564.

2. Beutin, L. 2006. Emerging Enterohaemorrhagic Escherichia coli, Causes and Effects of the Rise of a Human Pathogen. J. Vet. Med.; 53:299-305.

3. Bettelheim, K.A. and L. Beutin. 2003. Rapid laboratory identification and characterization of verocytotoxigenic (Shiga toxin producing) Escherichia coli (VTEC/STEC). J. Appl. Microb.; 95:205-217.

4. Salvador, A., et al. 2012. Development of a biphasic medium for detection of Shiga toxin-producing E. coli using Tetrahymena thermophila. ASM 112th General Meeting, San Francisco, CA .

5. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

6. Anderson, N.L., et al. Cumitech 3B; Quality Systems in the Clinical Microbiology Laboratory, Coordinating ed., A.S. Weissfeld. American Society for Microbiology, Washington, D.C.

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

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

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