Introduction
CHROMagar STEC is a selective medium designed for the detection of Shiga-Toxin producing E.coli (STEC), including non-O157 serotypes. It is the first of its kind available on the market, offering a unique solution for screening large numbers of samples.

Medium Performance
The medium allows easy reading as most STEC strains grow in mauve colonies, while other bacteria appear blue, colorless, or are inhibited. It is highly selective for STEC, making it an excellent tool for screening procedures. The medium can be supplemented with additional compounds to increase selectivity for specific outbreak strains.

Background
Recent studies have highlighted the prevalence of non-O157 STEC in foodborne outbreaks. The CDC has reported that non-O157:H7 serotypes are as common, if not more so, than O157:H7 infections. The USDA has declared six non-O157:H7 serogroups as adulterants in raw beef, which include O26, O103, O45, O111, O121, and O145.

Medium Description
The CHROMagar STEC base consists of 30.8 g/L of various components, including agar, peptone, yeast extract, salts, and a chromogenic mix. It is stored at 15/30°C with a pH of 6.9 +/-0.2 and has a shelf life of two years. The supplement included in the pack is freeze-dried and has a shelf life of three years.

Procedure
Samples such as food, environmental, and feces can be directly streaked onto the medium. Incubation is done for 18-24 hours at 37°C under aerobic conditions, with an optional prior enrichment step.

Quality Control Strains
Quality control strains include E.coli O157 ATCC 35150 (mauve colonies), E.cloacae ATCC 13047 (metallic blue colonies), E.coli ATCC 25922 (inhibited), and E.faecalis ATCC 29212 (inhibited).

Order References
Product references for ordering include a 1000 ml pack (ST160) and a 5000 ml pack (ST162), each containing a base powder and supplements.

Conclusion
CHROMagar STEC provides a reliable and selective medium for detecting a wide range of STEC serotypes, addressing the need for effective screening tools in food safety and public health.