Food scientists continue to roll out tools in the fight against foodborne pathogens as researchers in the US design a new biosensor to detect the potentially deadly bacteria Listeria monocytogenes.
The antibody-based fibre-optic biosensor created by food scientists at Purdue University can detect the listeria bacteria in less than 24 hours at concentrations as low as 1,000 cells per millilitre of fluid - equivalent to the size of a pencil rubber.
According to the researchers, the sensor is selective enough to recognise only the species monocytogenes.
Listeria monocytogenes (Lm), an emerging foodborne disease because the role of food in its transmission has only recently been recognised, can cause abortion and stillbirth, and in infants and persons with a weakened immune system it may lead to septicemia (blood poisoning) and meningitis.
The disease is most often associated with consumption of foods such as soft cheese and processed meat products that are kept refrigerated for a long time because Lm can grow at low temperatures.
Outbreaks of listeriosis have been reported from many countries, including Australia, Switzerland, France and the US. Two recent outbreaks of Listeria monocytogenes in France in 2000 and in the USA in 1999 were caused by contaminated pork tongue and hot dogs respectively.
Food safety experts estimate that 100 to 1,000 cells can cause the illness. Cooking kills most of the L. monocytogenes cells that can grow at refrigeration temperature, but ready-to-eat products, such as pates, smoked fish, cheeses and hot dogs, are not always cooked by consumers before consumption.
"The selectivity, sensitivity and rapidity of this sensor represent a vast improvement over the types of test kits that are currently available commercially," said Arun Bhunia , associate professor of food microbiology and one of the sensor's developers.
The bacteria classified as Listeria include six different species, but only L. monocytogenes can infect humans.
The sensor is made of a small piece of optical fibre - a clear, solid, plastic material that transmits light through its core. The fibre is coated with a type of molecule called an antibody, which specifically recognises L. monocytogenes and captures it, binding it to the fibre. When the fibre is placed in a liquid food solution, any L. monocytogenes in the sample will stick to the fibre.