Success Stories

But the investigation did not stop there. Authorities needed to know how the spinach became contaminated. Without that information, it could happen again.

It was a double stroke of luck and scientific readiness that the microbiology staff of the California public health laboratory’s Food and Drug Laboratory had been carefully refining the protocol for a revolutionary new technique, specific to E. coli O157:H7.

Using this technique on September 28, 2006, CA public health laboratorians subsequently isolated a matching strain of E. coli from cow feces in nearby fields.

The recirculating immunomagnetic separation (RIMS) technique uses paramagnetic beads coated with an antibody specific to E. coli O157:H7. The entire sample—taken from either food or environmental sources—is weighed, placed in an enrichment broth, and then pumped through the beads. E. coli O157 is separated and concentrated, essentially rendering the dangerous bacteria as a bigger target for common laboratory testing methods.

“The technique is especially useful with organisms that present in low numbers in samples with a high background of other organisms—such as cattle feces,” said Dr. Leta Crawford-Miksza, Chief of the Food Microbiology Section of California’s Food and Drug Laboratory Branch. “It has increased testing sensitivity at least a hundred fold.”

The public health laboratory’s microbiologists began experimenting in mid-2005, trying to improve their ability to identify the elusive E. coli O157:H7. In unison with two federal partners—the US FDA San Francisco District Office Laboratory and USDA ARS Laboratory in Albany (CA)—more than 800 samples were taken from the waterways of the Salinas Valley over a 15-month period.  

“We tested each batch differently,” said Crawford-Miksza. “We referred to published methods. We talked with colleagues. Finally RIMS is what worked.” After identifying the preferred technique, the laboratory began perfecting the protocol. The two federal laboratories also pursued the immunomagnetic separation techniques, but developed their own methods. These laboratories also isolated matching strains of E. coli, but the California public health laboratory did it first.

“Everybody at the lab worked on this,” said Crawford-Miksza. “We gathered in the conference room, writing all over the chalkboards, shouting over one another to get our ideas out. It was a product of incredible teamwork.”

The technique works so well that the International Association for Food Protection (IAFP) recognized the laboratory staff with its 2007 Food Safety Innovation Award. It was accepted on behalf of the staff by Dr. Sunee Himathongkham, the research scientist who led the lab’s efforts.

It’s also an affordable technology that can be easily implemented by laboratories across the country. With foodborne illness, speed is of the essence. Using RIMS to isolate E. coli O157:H7 trims the laboratory process by two days. Fewer people will get sick: food recalls can be issued earlier, investigators can trace the contamination back to its source, and regulating authorities can craft guidelines to prevent future occurrences.