Global climate change, changes in consumer preferences for certain types of foods, and large-scale farming practices, and the global market for fresh produce have focused attention on the potential role of the food supply chain on introducing food-borne and water-borne pathogens to people. Microbial contaminated food and water related diseases are major public health problem worldwide, with serious implications for both social welfare of populations and national economies. The Laboratory of Renewable Resources Engineering is working cooperatively with the USDA and the Purdue University Center for Food Safety Engineering (CFSE) to carry out fundamental research on detection and characterization of food pathogens, as well as to develop technologies for rapid detection of food pathogens. Included are Listeria monocytogenes, Salmonella Enteritidis, Escheria coli, and native microorganisms found in fresh vegetables, milk, processed meats, eggs, and water.
The Laboratory is working cooperatively with other collaborators within the CFSE and at other institutions for the rapid detection of pathogenic species using techniques ranging from immunoassays to PCR. A common denominator in all of these assays is the desire for rapid detection and accurate assessment of the potential risk of the presence of pathogens in various types of consumer products. Consequently, a major effort has been undertaken over a period of 10 years to study and characterize methods by which microorganisms and pathogens, if present, can be rapidly concentrated for the purposes of interrogating the samples for the presence of pathogens. Despite the development of rapid detection methods (such as ELISA and PCR) for food or water related borne pathogens, reduction and/or elimination of cultural enrichment remain an essential goal to attend the need for rapid pathogen detection in a possible contaminated sample. This has led to a major effort and fundamental studies on the role of membranes and microfiltration for rapid concentration of microorganisms derived from a range of food matrices. These methodologies are also being extended to other biological materials.
Current detection methods allow for bacteria quantitation in hours. However, the steps preceding detection may add days to the overall process. Therefore, there is an essential role for a time effective bacterial concentration and purification pre-analytical sample processing step. Microfiltration efficiently recovers bacteria, protozoa and viruses in foods or water related samples by reducing large samples to small volumes, increasing cell concentration so that interrogation for the presence of pathogens may proceed quickly. Although the concept is not new, membrane fouling limited the volumes of fluid that could be processed. Our research is addressing the fundamentals of membrane characteristics, microfluidics that control membrane stability, and the integration of protein interactions with both membrane components and microbial cells to develop a system where accelerated microfiltration with recovery of viable cells is reproducibly accomplished. We combine mechanical shearing and enzyme treatment with rapid microfiltration in a Cell Continuous Concentration Device (C3D) through special membranes. The small volume of concentrated and recovered cells contains the target bacteria at the level that can be effectively used for pathogen detection through different available technologies such as plating, qPCR, biochips, ELISA, and immunoassays.
The research upon which this work is based has carefully examined different types of filtration media, hollow fiber membranes, and automated systems that would enable them to be used in a hands-off manner. Progress in what would seem to be a relatively straightforward approach to capturing and concentrating microorganisms from either water or fluid extracts derived from various types of vegetable and plant materials is challenging because of the presence of numerous macromolecules, proteins, and other constituents in these fluids. These constituents cause the phenomena of concentration polarization, membrane fouling, and other effects that limit both the rate and extent to which large sample volumes might be concentrated to very small fluid elements. Our work is continuing to carry out fundamental research on defining membrane chemistry, extraction conditions, and automated control of the migration process in order to achieve rapid concentration of the microorganisms and a thousand-fold concentration of potential pathogens. When coupled with PCR and other detection methods, a time-to-result, i.e. the time that elapses when the sample is taken and detection methodology has been applied, is approaching 6 hours.