Blocking nonspecific adsorption of native food-borne microorganisms by immunomagnetic beads with ι-carrageenan Original Research Article

We present herein the partitioning characteristics of anti-Salmonella and anti-Escherichia coli O157 immunomagnetic beads (IMB) with respect to the nonspecific adsorption of several nontarget food-borne organisms with and without an assortment of well-known blocking agents, such as casein, which have been shown to be useful in other immunochemical applications. We found several common food-borne organisms that strongly interacted with both types of IMB, especially with anti-Salmonella form (av ΔG0=−20±4 kJ mol−1) even in the presence of casein [1% (w/v): ΔG0=−18±3 kJ mol−1; ΔΔG0∼−2 kJ mol−1]. However, when one of the most problematic organisms (a native K12-like E. coli isolate; ΔG0=−19±2 kJ mol−1) was tested for nonspecific binding in the presence of ι-carrageenan (0.03–0.05%), there was an average decline of ca. 90% in the equilibrium capture efficiency ξ (ΔG0=−11±4 kJ mol−1; ΔΔG0∼−8 kJ mol−1). Other anionic polysaccharides (0.1% κ-carrageenan and polygalacturonic acid) had no significant effect (av ΔG0=−19±1 kJ mol−1; ΔΔG0∼0 kJ mol−1). Varying ι-carrageenan from 0% to 0.02% resulted in ξ significantly diminishing from 0.69 (e.g., 69% of the cells captured; ΔG0=−19±3 kJ mol−1) to 0.05 (ΔG0=−11±2 kJ mol−1; ΔΔG0∼−9 kJ mol−1) at about 0.03% ι-carrageenan where ξ leveled off. An optimum blocking ability was achieved with 0.04% ι-carrageenan suspended in 100 mM phosphate buffer. We also demonstrated that the utilization of ι-carrageenan as a blocking agent causes no great loss in the IMBs capture efficiency with respect to the capture of its target organisms, various salmonellae.