Food contamination can be checked by turning off lights

Purdue University researchers have engineered a new detection method that would enable them to traces E. coli (bacteria) contamination in food by turning off the lights to see if the bacteria glow in the dark.

The bacteriophage called NanoLuc is a virus that only infects bacteria to produce an enzyme that causes E. coli O157:H7 to emit light if infected.

The process can shave off hours traditional testing methods, which can be critical when stopping the distribution of tainted foods.

Researcher Bruce Applegate said, "It's really practical. They (testing labs) don't have to modify anything they're doing. They just have to add the phage during the enrichment step of the testing protocol."

Adding, "We could detect as few as four bacteria in eight hours, and the process is cheaper than tests being used today."

While many strains of E. coli bacteria are harmless, some can cause severe and potentially fatal illnesses.

Ingesting as few as 10 colony-forming units of E. coli can result in serious illness.

Current detection methods cannot find just a few E. coli cells in a sample, so inspectors do an enrichment process, culturing the bacteria to multiply so they can be detected.

With the bacteriophage added to the sample, scientists can add a reagent and detect E. coli before the enrichment process is even finished, within seven to nine hours.

Paper's first author Dandan Zhang, said: "The current detection methods cannot bypass the enrichment process, but our technology can explore the enrichment phase. That can give us a time advantage over other methods."

The process is also unlikely to create a false positive because the bacteriophage cannot produce the light-emitting protein without encountering E. coli, which is the only bacterium NanoLuc is able to infect.

"The phage is just a virus. It cannot carry out metabolism until it infects bacteria, which in this case is E. coli. They won't create these proteins unless they've found their specific host," Applegate said.

Based on the number of bacteriophage added, the amount of time that has passed and the amount of light emitted, the authors can use an equation to determine approximately how much E. coli is present.

Their tests were done in an enrichment broth made with ground beef.

Zhang said future work would focus on detection of E. coli in lettuce, spinach and other produce.

Other bacteriophages could also be developed to detect other pathogenic bacteria, such as Salmonella, in a similar fashion.