Magnetized carbonyl iron and insoluble zirconium hydroxide mixture facilitates bacterial concentration and separation from nonfat dry milk.

A mixture of magnetized carbonyl iron and insoluble zirconium hydroxide was investigated for its ability to concentrate various foodborne pathogens from 25-ml samples of reconstituted nonfat dry milk. Each sample was artificially contaminated with 10(3) to 10(6) CFU/25 ml of representative foodborne pathogens (Salmonella enterica serovar Enteritidis, Listeria monocytogenes, and Bacillus cereus spores) and processed for bacterial concentration with high-speed centrifugation for the primary concentration followed by a secondary concentration step involving the carbonyl iron-zirconium hydroxide mixture. Bacterial recoveries, as evaluated on the basis of loss to discarded supernatants, exceeded 75% for all organisms at all inoculum levels and were usually >90%. Recovery was confirmed by direct plating of the immobilized pellet, for which the valueswere similar albeit more varied. Additional experiments confirmed that the magnetized carbonyl iron-insoluble zirconium hydroxide mixture was relatively nontoxic to both Salmonella Enteritidis and L monocytogenes Overall, the entire concentration scheme resulted in a 25-fold reduction in sample volume with the recovery of viable bacterial cells. This novel compound shows promise for facilitating inexpensive, rapid, and effective bacterial concentration in food systems.