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Title: IMMUNO-MAGNETIC BEAD MASS TRANSPORT II: CAPTURE EFFICIENCY AT HIGH TARGET CELL DENSITIES IN PHOSPHATE-BUFFERED SALINE

Author
item Irwin, Peter
item Damert, William
item Tu, Shu I

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2003
Publication Date: 5/1/2004
Citation: Irwin, P.L., Damert, W.C., Tu, S. 2004. Immuno-magnetic bead mass transport ii: capture efficiency at high target cell densities in phosphate-buffered saline. Applied and Environmental Microbiology.

Interpretive Summary: Food-borne pathogen contamination is a serious public health problem. To minimize possible outbreaks of food poisoning by bacteria such as Salmonella, sensitive and rapid detection techniques are needed to bring about proper procedures prior to the distribution of contaminated foods to consumers. Conventional microbiological approaches require a complex set of procedures, which can take days, to increase the pathogen's population size to detectable levels. Thus, an alternative process which rapidly concentrates targeted pathogens in foods is needed. One attractive approach is to capture, and therefore concentrate, pathogens by specific antibodie coated on small magnetic beads. Since the beads can be cleanly separated from other components by the use of ordinary magnets, this approach has gained increased attention. However, there is no systematic theoretical analyses on many important parameters critical to the practical lapplication of these immuno-magnetic beads (IMBs). In this work we have created mathematical models which describe the interactions between Salmonella and IMBs. We have used this new model to predict the bacterial capture efficiency and best mixing time for capture. Excellent agreements were obtained between predicted and observed values. These results are important for the application of IMB for capturing pathogens in food. The information is useful for food microbiologists and instrumentation specialists in the development of standard procedures for using the IMB capture/concentration technique in high throughput laboratories.

Technical Abstract: In this manuscript we present a modified mass transport-based kinetic model for capture efficiency (E) variation with mixing time (tmix) which is applicable for all immuno-magnetic bead (IMB):target cell concentrations (dIMB about 8000000 IMB/mL; dcells = 1-10000000 CFU/mL). As S. enteritidis concentrations (dcells) were increased from about 100 to nearly 100000000 CFU/mL we observed that the average number of cells captured per IMB-cell complex increased from 1 to about 4. Concurrently, using the modified kinetic model for fitting E variation with tmix, we observed that the maximum possible level of capture (Emax; E = Emax at equilibrium) decreased from about 100 (dIMB much greater than dcells) to 23% (dIMB:dcells about 0.1). Across all S. enteritidis concentrations tested (dIMB:dcells = 200000, 200, 3, and 0.1), the mass transport coefficient (gamma) averaged {3.18 +/- 1.60} * 1000000000 mL/{IMB min}. By inserting our classically-derived equation for gamma into the kinetic model and solving for the IMB radius (rIMB), we found that the apparent rIMB was 2.14 +/- 0.85 micrometers (averaged across all dIMB:dcells). Since the rIMB value reported by the manufacturer (1.4 micrometers) fell within the 95% confidence interval for the apparent rIMB, these results lend support to our hypothesis that the capture dynamics of target cells is controlled exclusively by IMB mass transport.