E. coli OK O pool for detection of Big Six non-O157 STEC/ VTEC serotypes
In addition to continued testing for E. coli 0157:H7, U.S. regulations have, since 2012, required the meat industry have to monitor for six non-O157 Shiga toxin-producing E. coli (STEC, also called Verocytotoxin-producing E.coli (VTEC)) serogroups O26, O45, O103, O111, O121, and O145, commonly known as the “Big Six”1.
These six serotypes have been most frequent associated with E. coli outbreaks of food-borne illnesses worldwide and can cause outbreaks of hemorrhagic colitis (bloody diarrhea) and hemolytic uremic syndrome (kidney failure).
Any products testing positive for these STEC serogroups are considered adulterated and prevented from entering commerce.
In 2023, the United States Department of Agriculture (USDA) expanded testing requirements to cover a broader range of raw beef products2.
Product description
The OK O pool Big Six is intended for screening of the serotypes O26, O45, O103, O111, O121, and O145 using slide agglutination. The test is supplied in 3 mL bottles – enough to perform 150 tests. All six antisera can also be provided as single antisera. Shelf life is minimum one years from date of shipment. Storage conditions are 2–8 °C. All products are absorbed free of cross-reactions within the OK O pools.
How to use
Place a small drop (approximately 20 μL) of antisera on a glass slide. Transfer culture from two to three colonies to the drop of antiserum and mix well. A positive result will be visible to the unaided eye as agglutination within 10 seconds. Positive slide results need to be confirmed with O antisera for boiled culture.
Product range
| Article number | Product | Number of tests | Packing |
|---|---|---|---|
| 88010 | OK O pool Big Six | 150 | 3 mL |
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FAQ:
The strain is likely rough. This can be tested by agglutinating with saline as a negative control. If the negative control is positive, the strain is rough. Rough strains cannot be serotyped. However, a rough strain can be converted to a non-rough strain as follows: Suspend a small amount of colony from a nonselective agar plate in saline (not broth), boil for ≥1 hour, and use the boiled suspension for O serotyping. If unsuccessful, flood a fresh nonselective plate with ethanol, dry it, inoculate the rough colony, then repeat the boil and serotype procedure.
OK O antisera are for screening of whole bacteria. Whole bacteria have multiple surface antigens, increasing the possibility of non-specific reactions. When boiling the bacteria, these surface antigens denature, leaving only the O antigen.
Read positives within the first 10 seconds; after ~20 seconds, sliding can cause nonspecific reactions. Using too much colony mass may show lumps that are not true agglutinations.
E. coli OK O antisera are for live bacteria screening (quick result ~10 seconds) from a non-selective agar plate. O antisera on boiled culture are for full serotyping. The OK O antisera results need to be confirmed with O antisera for a definitive serotyping.