Developing a Listeria monocytogenes biosensor for soft cheeses
- Listeria monocytogenes -
About Listeria monocytogenes -
Listeria monocytogenes is a gram positive, food borne pathogen responsible for Listeriosis. It is a particular threat as it can survive a range of pH’s as well as temperatures as low as 0°C allowing it to survive in industrial and domestic refrigerators. This pathogen commonly contaminates unpasteurised dairy products, particularly soft cheeses, as well as fresh vegetables and cooked meats. The presence of as little as 100 L. monocytogenes cells per gram of food can lead to symptoms ranging from fever, diarrhoea and muscle aches to more severe ailments such as meningitis and sepsis. Whilst in the majority of healthy people listeriosis manifests itself with flu-like symptoms, it can be fatal for immunosuppressed individuals like people suffering from AIDs or pregnant women who can suffer from fetal infections and miscarriage.
*Create a timeline of Listeria Outbreaks*
- The Problem & Our Solution -
There are currently tests to detect the presence of Listeria, these include the Anton Test or the Rapid Neogen Test. Although, both have their own drawbacks. The Anton Test is time-consuming, taking 24 hours and involves inoculating the conjunctiva of a guinea pig or rabbit to invoke an immune response. In contrast, the Rapid Neogen Test only takes 60 minutes, however, the machinery required is expensive costing around $11,000, which is often too much for small scale businesses.
Our project aims to improve Listeria testing particularly in soft cheeses, by developing a biosensor that is fully integrated into the soft cheese starter culture. The biosensor would detect the Listeria signalling molecule, autoinducing peptide (AIP), to trigger a significant color change (to purple) in the product, allowing for fast detection of Listeria either during the cheese making process or at anypoint of the products shelf life. We hope to accomplish this by transferring the AIP responsive genes from Listeria into Lactococcus lactis, the most common species utilised as a starter culture for cheese manufacturing.
- Agr Quorum Sensing in Listeria Monocytogenes -
The agr gene regulatory system is involved in biofilm formation and virulence in L. Monocytogenes(3). Homologs of the system in other bacteria, but this one is specific to listeria.
- What is AIP? -
AIP is highly specific to L.monocytogenes although other AIP molecules are produced by homologous species. AIP is a cyclic pentapeptide with the amino acid sequence CFMFV forming a thiolactone ring.
