Testing for Non-0157 STECs Leads to Development of New Lab Technology

Finally, the data analysis package provides automated data interpretation so that the user can easily decide how to proceed with a sample. An instrument display shows the presence or absence of a pathogenic STEC and lets the user know when a sample needs to be rerun due to unclear results.

One of the most significant benefits of the workflow is time to results. The system can clear a negative sample in a total of 10 hours—eight hours to enrich the sample plus the two hours it takes to perform the assay. The second assay, to confirm the presence of O157 or a non-O157 STEC, takes only an additional hour.

“Saving time is everything for the end user (producer or service lab). They have beef products, a perishable product, sitting in temperature-controlled storage locations, and the clock is ticking on getting a safe product into their distribution channel,” Liu said. “They also have to make sure they get an accurate answer. We offer a faster detection workflow, but we also have an optimized assay which offers high sensitivity and high accuracy.”

In addition, the hands-free, automated sample prep facilitates a high throughput. Establishments that test a large volume of samples—upwards of 60 at a time—want the speed and efficiency of starting a sample and, after performing a minimal number of steps, moving on to other tasks.

The system is used primarily by private establishments in the food industry, including slaughterhouses and food processing plants, as well as third-party labs that offer testing services to companies lacking this capability.

A popular Big Six testing system for federal and state government testing labs, RapidCheck and RapidChek CONFIRM, supplied by Romer Labs of Newark, Del., includes two test strips that identify all of the Big Six serogroups. Each strip tests for three of the targeted strains, with one strip sensitive to O103, O45, and O26 and the other to O145, O121, and O111. A sample of beef is enriched in media for eight to 18 hours, depending on sample size. After enrichment, 1 mL of the broth is transferred to a test tube, and both strips are inserted. The results can be read in 10 minutes.

The test strip technology offers labs several advantages. The short time to results after enrichment allows for rapid sample clearance and, therefore, rapid product release. The strips are cost effective and easy to use, requiring no special instrumentation or training. The system can be used with the RapidChek proprietary enrichment media or the widely available TSB, modified with the addition of novobiocin, an antibiotic.

Should the test strip screening indicate that a sample is positive, the next step is to confirm the presence of the pathogen with RapidChek CONFIRM. Tim Lawruk, Romer Labs’ senior director of sales and marketing, explained, “Once you have a potential positive from the screening test, you may perform cultural confirmation. RapidChek CONFIRM does that using an immunomagnetic separation kit. This allows you to isolate just the pathogen of interest during cultural confirmation, and not any other organism that may have grown in the enrichment media.”

To definitively identify a pathogen of interest, the technology concentrates target pathogens and washes away competing organisms. It uses antibodies specific to each of the targeted strains. These antibodies are attached to separate, coated magnetic particles. The reagent is added to 1 mL of the potentially positive enrichment and incubated for 15 minutes at room temperature. The sample tubes are then placed in the kit’s magnetic rack for five minutes, allowing the magnetic particles to bind the non-O157 strains using the antibodies. The remaining solution is discarded, and the bound material is washed, reconstituted, and plated on selective agars. The process requires no additional equipment or specialized training.