Mass spectrometric identification of pathogens in foods using a zirconium hydroxide immobilization approach

The analysis of bacteria in foods is a challenge because the food matrices might severely interfere with bacterial detection. Pathogens in milk/pudding/coffee were isolated with magnetized zirconium hydroxide, directly cultivated without colony isolation, and then analyzed using MALDI and LC-MS/MS. The analysis was less time-consuming than conventional biological methods because a colony isolation procedure was not required. Further, the MS analysis of bacteria was broad-spectrum detection that did not need prior knowledge of the target information such as DNA sequences, as required in PCR detection. The results showed that the bacteria stayed alive when attached to the synthesized magnetic metal hydroxide. We could concentrate and identify both Gram-positive (Enterococcus faecalis and Staphylococcus aureus) and Gram-negative (Escherichia coli and Vibrio parahaemolyticus) bacterial cells using the magnetized zirconium hydroxide immobilization approach. The detection limit of E. faecalis spiked into milk was down to a level as low as 32 CFU/mL when cultivation of the isolated bacteria was performed prior to MS analysis. The immobilization-based MS approach is simple and allows analysis of microorganisms in complex food samples. (C) 2011 Elsevier B.V. All rights reserved.