Improving Rapid Detection Methods for Foodborne Pathogens.

Researchers at Georgia Tech Research Institute (GTRI) have developed a microfluidic device that exploits cell movement to separate live and dead bacteria during food processing. The food processing industry is interested in technologies or methods that can quickly and accurately detect viable (live) bacteria, as these are the pathogens that can cause illness.Common foodborne pathogen screening methods like polymerase chain reaction (PCR) use DNA-based methods to perform the detection. However, because both viable (live) and non-viable (dead) bacteria contain the same DNA and other properties, it is difficult to distinguish between them without performing additional time-consuming incubation and culturing steps. Researchers at the Georgia Tech Research Institute (GTRI) have developed a microfluidic device that exploits cell movement to separate live cells from dead ones for real-time pathogen detection.The phenomenon known as chemotaxis is the movement of an organism in response to a chemical stimulus. For example, live bacteria naturally sense nutrient molecules such as sugars and amino acids and move toward them. Dr Jie Xu, GTRI research scientist and project director, explained: “The hypothesis is that by changing the local environment of the cells, their movement can be manipulated so all the viable cells can be separated and concentrated. This would improve the probability of detection and also provide a high level of confidence that viable cells are being detected.” GTRI’s chemotaxis-based microfluidic device consists of a 100-micrometre thick nitrocellulose membrane layer engraved with a micron-sized centre channel to contain the bacteria-laden sample. Two additional side channels are engraved into the same membrane layer that contains nanometer-sized pores that allow the formation of a chemical gradient across the center channel. The bacteria interact with these chemicals in the centre channel and then move based on the nature of these interactions, either toward it if it is a food source or away if it is a repellant. The separated bacteria are then collected in the channel’s respective outlets In recent experiments, E. coli 0157:H7 was used as the model bacterium, and aspartic acid (an attractant) and nickel ion (a repellent) were used as the chemotactic effectors. Researchers found the chemical gradients inside the channel can be maintained for an extended period. They also observed the cell population shift toward the side channel with attractant when live cells flowed inside the center channel, while the dead cells remained in the primary flow stream and exited the center channel.continue