Researchers Develop Tool For Rapid Salmonella Detection

WEST LAFAYETTE, Ind.Researchers at Purdue University have developed a system that concentrates foodborne Salmonella and other pathogens faster than conventional methods by using hollow thread-like fibers that filter out the cells, representing a potential new tool for speedier detection, according to a research paper that will be published in the journal Applied and Environmental Microbiology in November.

The discovery comes as the nation is immersed in a Salmonella Heidelberg outbreak that has been linked to raw chicken processed at three Foster Farms facilities in California. To date, 317 people have been sickened in 20 states and Puerto Rico.

Purdue has filed a patent application for the machine called a continuous cell concentration device, which could make it possible to routinely analyze food or water samples to screen for pathogens within a single work shift at food processing plants.

"This approach begins to address the critical need for the food industry for detecting food pathogens within six hours or less," said Michael Ladisch, a distinguished professor of agricultural and biological engineering at Purdue University. "Ideally, you want to detect foodborne pathogens in one work shift, from start to finish, which means extracting the sample, concentrating the cells and detection."

The first step in detecting foodborne pathogens is concentrating the number of cells in test samples. The new system enables researchers to carry out the concentration step within one hour, compared to a day for the standard method now in commercial use. Findings showed the system was able to concentrate inoculated Salmonella by 500 to 1,000 times the original concentration in test samples. This level of concentration is required for accurate detection. Another finding showed the system recovered 70% of the living pathogen cells in samples.

"This is important because if you filter microorganisms and kill them in the process that's self-defeating," Ladisch said. "The goal is to find out how many living microorganisms are present."

The machine was used to concentrate cells in a sample of chicken meat. The sample is first broken down into the consistency of a milkshake and chemically pretreated to prevent the filtering membranes from clogging. The fluid is then passed through 12 hollow-fiber filters about 300 microns in diameter that are contained in a tube about the size of a cocktail straw. The filtering process continues until pathogens if present are concentrated enough to be detected.

The technique, developed by researchers from Purdue's colleges of Engineering and Agriculture, could be performed during food processing or vegetable washing before the products are shipped. The U.S. Department of Agriculture (USDA) will test the system, which is not yet ready for commercialization. One feature that could make the machine practical for commercial application is that it can be quickly cleaned between uses since the tubes are flushed with sodium hydroxide and alcohol.