Rapid detection of Salmonella typhimurium in chicken carcass wash water using an immunoelectrochemical method

An immunoelectrochemical method coupled with immunomagnetic separation was developed for rapid detection of Salmonella Typhimurium in chicken carcass wash water. Samples of chicken carcass wash water were inoculated with Salm onella Typhimurium at different cell numbers. Possible nonspecified inhibit ors in the wash water were minimized by filtration and centrifugation. An a pproximately 9.4% toss of Salmonella cells was found after filtration (P < 0.01). The samples were mixed with anti-Salmonella-coated magnetic beads (A SCMB) and alkaline phosphatase-labeled anti-Salmonella (APLAS) to form ASCM B-Salmonella-APLAS conjugates. The conjugates were separated from the solut ion using a magnetic separator and then incubated with phenylphosphate subs trate to produce phenol. The number of Salmonella was determined by measuri ng the phenol concentration using an amperometric tyrosinase carbon paste e lectrode in a flow injection analysis system. Under optimized parameters (1 mM MgCl2, 0.2 mu g/ml APLAS, and 1 mM phenylphosphate in pH 7.0 Tris buffe r solution), Salmonella Typhimurium in chicken carcass wash water could be identified and enumerated within 2.5 h with a detection limit of 5 x 10(3) CFU/ml. A linear relationship on a log-log scale was found between Salmonel la cell number and the peak current ratio for Salmonella concentrations ran ging from 10(3) to 10(7) CFU/ml (R-2 = 0.963). The peak currents of multiba cteria samples, containing Salmonella Typhimurium, Listeria monocytogenes, and Campylobacter jejuni, were not significantly different from Salmonella- only samples (P > 0.01).