Large‐volume Filtration for Recovery and Concentration of Escherichia Coli O157:h7 From Ground Beef*

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 assay systems (100–100,000 cfu/mL). Although filtration can potentially separate and concentrate bacterial pathogens to detectable levels if large (100–1,000 mL) sample volumes are processed, prior filtration methods failed to approach these volumes because of the high solids content and viscosity of typical food samples. This report describes a novel three‐stage filtration system based on a leukocyte removal filter, a glass fiber prefilter, and a membrane capture filter. Data are presented on factors (e.g., particle size, bacteria binding, pH) affecting filtration performance and protocol design. Escherichia coli O157:H7 at less than 1 cfu/g were quantitatively recovered from 10 g of stomached ground beef in 15 min, and detected on selective media within 24 h. PRACTICAL APPLICATIONS The methodology presented in this study allows the rapid concentration of Escherichia coli O157:H7 from the large volumes of stomached ground beef. The primary application is in rapid biosensor detection and quantitation of low levels of pathogens in foods without enrichment. The isolated bacteria can be recovered in a volume of ∼20 µL and are virtually free from interfering sample constituents, allowing facile detection by polymerase chain reaction and other approaches. This filtration methodology may also be useful for studies on attachment and partitioning of bacteria on food surfaces, as free and bound bacteria can be rapidly separated at low concentrations reflecting actual contamination situations.