On the Fast Track
A student who hasn’t prepared for an exam can wait forever for the test results. A food company testing for the presence of bacterial pathogens can’t get the results soon enough.
“For foodborne pathogen outbreaks, a rapid detection is critical to prevent fast spreading of pathogens and to prevent outbreaks of illnesses and/or mortality,” said Bosoon Park, lead scientist of the USDA-ARS Russell Research Center in Athens, Ga.
That anxious wait for results may be shrinking, as newer and faster testing methods are coming into play, from public sources such as the Russell Center and private companies.
All in the timing
The timing of test results depends on the method used, said Ratul Saha, Ph.D., a research scientist specializing in microbiology for NSF International, which offers auditing and certification of human health and safety practices, including food safety sanitation.
“(The) conventional microbiological method using bacteriological media takes two to three days for results and up to seven to 10 days for conformation,” said Saha.
The common antigen-antibody testing method, known as ELISA enzyme-linked immunosorbent assay, can be completed in two to four hours. Another form of the test yields results in 10 to 15 minutes, but requires a higher number of bacterial cells for detection.
Two more methods coming into use are DNA-based and biosensors, said Saha.
“DNA-based methods have a faster turnaround time, such as one to two days, and also offer better sensitivity and specificity … Biosensors are known to detect pathogens within 30-90 minutes and are also very sensitive,” said Saha.
Park’s team at the Russell Center is taking the biosensor approach, working on several optical pathogen detection methods, including one called SERS (surface-enhanced Raman scattering) for Salmonella testing, and a similar method called FT-IR. These biosensors work by applying fluorescent organic dye particles to Salmonella antibodies. Upon contact with the pathogen, the dye illuminates for easy detection.
“These optical methods are able to detect critical optical characteristics (fingerprints) of biochemical composition and structural features of pathogens and help in faster detection (from half an hour up to two hours),” said Park.
In April, Neogen Corporation of Lansing, Mich., introduced its ANSR test for Salmonella. The ANSR system falls into the category of DNA-based testing. The system works by using an isothermal amplification reaction test method that amplifies the DNA of any bacteria present to detectable levels in 10 minutes. Combined with ANSR’s single enrichment step, the new method can provide DNA-definitive results for Salmonella in as little as 10 hours from the time of the sample, according to Neogen.
“The ANSR system reduces the detection time from days to hours and the assay time is 10 minutes once the sample is inside the ANSR instrument,” said Gerry Broski, Neogen’s senior marketing director for food safety.
Broski added that Neogen’s new system is “cost competitive” with older systems and easy to use.
“After enrichment of the sample, the steps for the ANSR Salmonella assay are very simple. 1. Lyse (chemically separate) the sample; 2. Incubate the reaction; and 3. Read the results,” he said.
ABC Research Laboratories, based in Florida, has come up with its own way of speeding test results by using its Laboratory Information Management System (LIMS).
“Our LIMS is a web-based system that allows us to track samples internally and also allows our clients secure access to their testing results 24 hours a day, seven days a week from the web,” said Gillian Dagan, chief scientific officer for ABC. “When a sample arrives to our lab, it is logged into LIMS with a sample description and assigned a unique identification number. All tests to be performed are also logged into the system and when each test is complete, the data is entered into LIMS as well.
“This provides seamless tracking of samples and results for both our scientists and our clients.”
The end result of any testing method is the best combination of three factors, said the USDA-ARS’s Park: sensitivity (which describes the limit of detection), specificity (which eliminates errors) and speed.
Researchers are looking for a way to accomplish all three of these objectives with one process; existing methods tend to be strong in one or two of these areas, while falling short in another, he explained.
“No sensing technologies are available to meet those entire three requirements for a practical use,” he said. “Most currently available methods to detect pathogens need long processing time, especially incubation time for samples to meet the detection limits.”
Said Broski, “Microbiological detection of pathogens is not easy because you are dealing with living organisms which don’t follow the same rules as a chemical contaminant, such as a pesticide.”
Though faster results are desired, accuracy still must trump speed.
“High sensitivity of a rapid pathogen test is imperative,” said Dagan. “The test must be able to detect one cell and because that cell may be partially damaged, the testing includes incubation and resuscitation time to insure that if the pathogen is present, it is detected.”
--By Lee A. Dean, Fresh Cut contributor
The commercially available DuPont Qualicon BAX system is used for the detection of specific foodborne pathogens. Courtesy of NSF.
Real-Time PCR is applied to detect and quantify a wide variety of pathogens in food. Courtesy of NSF.