Submitted to: Journal of Rapid Methods and Automation in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 3, 2008
Publication Date: February 1, 2009
Citation: Brewster, J.D. 2009. Large-volume filtration for recovery and concentration of E. coli O157:H7 from ground beef. Journal of Rapid Methods and Automation in Microbiology. 17:242-256. Interpretive Summary: Rapid, sensitive assays capable of detecting small numbers of pathogenic bacteria in foods are needed by regulatory inspection personnel and others in agriculture and food industries working to reduce foodborne illnesses, such as those caused by E. coli O157:H7. Current techniques are not able to detect very low levels of pathogens, so it is necessary to culture samples for period of time to allow the pathogen to grow and increase in concentration before detection. This enrichment process adds many hours to the assay, and may fail if the sample contains other benign microorganisms which grow more rapidly than the pathogen. To overcome this problem, a new method for concentrating pathogens in ground beef has been developed. A series of filters was then used to separate the pathogen and trap it on a small pore filter membrane. By concentrating the pathogens from a large sample into a small volume (less than a drop of water), this process serves the same purpose as enrichment, but is much faster. The effect of homogenizing conditions and filter type was studied to determine the optimum conditions for capture. Future research will link this concentration process to a number of existing detection methods to produce rapid, sensitive pathogen assays.
Technical Abstract: Rapid assays for foodborne pathogens currently require an enrichment step to bridge the gap between the detection limit of interest (1 cfu/g or less) and the detection limits of available sensors and assay systems (100 - 100,000 cfu/ml). Many assays also require immunomagnetic or other separation steps to remove interfering substances prior to detection of the target pathogen. These enrichment and separation steps add many hours to the assay time, largely offsetting the advantages of rapid detection technology. Filtration of food samples can potentially be used to separate and concentrate bacterial pathogens to detectable levels if large (100 - 1000 ml) sample volumes can be processed. However, the high solids content and viscosity of typical food samples such as stomached meats has limited conventional filtration methods to sample volumes of a few ml. Systematic development of effective filtration methods requires data on the properties of filter materials and food samples that is currently unavailable. Data on the retention of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enteriditis on a wide variety of filters is presented, along with particle size distributions of stomached ground beef, ground chicken, and hot dogs. The effect of diluent on filtration of stomached ground beef is discussed, and a protocol for single-step concentration and recovery of Escherichia coli O157:H7 from 100 ml of sample in 30 min is described.