| Listeriosis, caused by Listeria, is a major foodborne illness. Since infection is often associated with low levels of contaminating cells, concentration of cells and their separation from the food sample matrices are necessary prior to detection, whether by conventional or rapid techniques.; In the first part of the study a simple procedure for metal hydroxide preparation and immobilization of bacteria was developed. The procedure was used to compared cell immobilization on three metal hydroxides including calcium phosphate (hydroxyapatite, HA), zirconium (ZrOH), and titanium (TiOH). L. monocytogenes strain Scott A (serotype 4b) in liquid culture media was used as the test organism. Results showed immobilization and concentration of L. monocytogenes cells by all three metal hydroxides tested. However, HA consistently showed the highest immobilization efficiency of 85% to 95% in tests with 103--10 7 cells. Viability of the immobilized cells and an estimate of the immobilization efficiency were confirmed by tests with the automated optical system (Solaris, Ann Arbor, MI). Tests other bacterial species in liquid media resulted in similar immobilization efficiency, demonstrating concentration of both Gram positive and Gram negative pathogens. Not until initial cell levels reached beyond 108 CFU did 0.01 g HA appear saturated. Moreover, immobilization and detection of 103 L. monocytogenes cells was undisturbed in the presence of 107 cells of competing organisms (Salmonella Enteritidis).; A food model system consisting of sterile comminuted beef was used to further test the procedure. (Abstract shortened by UMI.)... |
