HiCrome™ Shiga Toxin EC Agar Base

Intended use

It is chromogenic differential medium for selective isolation of Shiga toxin producing E.coli from clinical and nonclinical samples.

Composition**

Final pH ( at 25°C): 6.9±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 32.50 gram in 1000 ml purified / distilled water. Heat to boiling to dissolve the medium completely. DO NOT AUTOCLAVE. Cool to 45-50°C. Aseptically add the rehydrated content of two vials of SEC Selective Supplement (FD354) . Mix well and pour into sterile Petri plates.

Principle and Interpretation

Shiga toxin producing E.coli first emerged as a ground beef associated outbreak of serotype O157: H7. It was initially isolated on MacConkey Sorbitol Agar Base, however non-O157 serotypes of Shiga toxin producing E.coli could not be differentiated (1). Certain non EC O157 Shiga toxin producing E.coli are usually sorbitol fermenting strains and hence Mac sorbitol Agar fails to detect this organisms, posing a problem in its detection.

Shiga toxin producing E.coli is responsible for an array of diseases including mild gastro enteritidis and hemorrhagic colitis to even life threatening haemolytic-uremic syndrome (2).

Peptone special provide nitrogenous and carbonaceous compounds, long chain amino acids, vitamins and other essential nutrients. Buffer mixture helps in buffering the medium. Chromogenic mixture in the medium imparts mauve to purple colour to Shiga toxin producing E.coli strains. Other Enterobacteriaceae strains appear as colourless or blue coloured or are inhibited. Selective supplement added to the medium suppresses the growth of gram positive and other contaminating organisms.

Type of specimen

Clinical samples : Stool, urine samples, etc.; food and dairy samples

Specimen Collection and Handling

For clinical samples follow appropriate techniques for handling specimens as per established guidelines (3,4).

For food and dairy samples, follow appropriate techniques for sample collection and processing as per guidelines (5,6).

After use, contaminated materials must be sterilized by autoclaving before discarding.

Warning and Precautions

In Vitro diagnostic use. For professional use only. Read the label before opening the container. Wear protective gloves/protective clothing/eye protection/face protection. Follow good microbiological lab practices while handling specimens and culture. Standard precautions as per established guidelines should be followed while handling clinical specimens. Safety guidelines may be referred in individual safety data sheets.

Limitations

1. Further biochemical and serological tests must be performed for final confirmation.
2. Due to varying nutritional requirements certain strains may show poor growth
3. Certain non Shiga toxin producing E.coli may produce mauve coloured colonies.

Performance and Evaluation

Performance of the medium is expected when used as per the direction on the label within the expiry period when stored at recommended temperature.

Quality Control

Appearance Cream to yellow homogeneous free flowing powder

Gelling Firm, comparable with 1.2% Agar gel

Colour and Clarity of prepared medium Light amber coloured, clear to slightly opalescent gel forms in Petri plates

Reaction Reaction of 3.25% w/v aqueous solution at 25°C. pH : 6.9±0.2

pH 6.70 - 7.10

Cultural Response M2092: Cultural characteristics observed after an incubation at 35-37°C for 24 -48 hours.

Key : (*) Corresponding WDCM numbers.

Storage and Shelf Life

Store between 15-25°C in a tightly closed container and the prepared medium at 2-8°C. Use before expiry date on the label. On opening, product should be properly stored dry, after tightly capping the bottle in order to prevent lump formation due to the hygroscopic nature of the product. Improper storage of the product may lead to lump formation. Store in dry ventilated area protected from extremes of temperature and sources of ignition Seal the container tightly after use. Product performance is best if used within stated expiry period.

Disposal

User must ensure safe disposal by autoclaving and/or incineration of used or unusable preparations of this product. Follow established laboratory procedures in disposing of infectious materials and material that comes into contact with clinical sample must be decontaminated and disposed of in accordance with current laboratory techniques (3,4).

Reference

1. Heuvelink AE, van de Kar NC, Meis JF, Monnens LA, Melchers WJ . 1995. Characterization of verocytotoxin producing Escherichia coli O157 isolates from patients with haemolytic uraemic syndrome in Western Europe. Epidemiol. Infect. 115:1–14
2. Karch H, Tar Pl, Bielaszewska M.2005. Enterohaemorrhagic Escherichia coli in human medicine. Int.J. Med MicrobioloL,295:405-418.
3. Isenberg, H.D. Clinical Microbiology Procedures Handbook. 2nd Edition.
4. Jorgensen, J.H., Pfaller , M.A., Carroll, K.C., Funke, G., Landry, M.L., Richter, S.S and Warnock., D.W. (2015) Manual of Clinical Microbiology, 11th Edition. Vol. 1.
5. Salfinger Y., and Tortorello M.L., 2015, Compendium of Methods for the Microbiological Examination of Foods, 5th Ed., American Public Health Association, Washington, D.C.
6. Wehr H. M. and Frank J. H., 2004, Standard Methods for the Microbiological Examination of Dairy Products, 17th Ed., APHA Inc., Washington, D.C.