DETECTION OF VIABLE LISTERIA MONOCYTOGENES IN MILK USING AN ELECTROCHEMICAL METHOD

Abstract Growth of Listeria monocytogenes in a Listeria enrichment broth (LEB) was automatically monitored by electrochemical cyclic voltammetric scan using a gold working electrode. Changes in cyclic voltammograms were observed during growth of L. monocytogenes in LEB. The reduction peak at −0.4 V (vs Ag/AgCl) corresponding to the reduction of oxygen dissolved in LEB on cyclic voltammograms was decreasing with proliferation of L. monocytogenes, and disappeared eventually. A pair of reversible redox peaks appeared during growth of L. monocytogenes in LEB. These cyclic voltammetric characteristics can be used to detect L. monocytogenes in various samples. Threshold values (detection time) obtained from the oxygen consumption curves were inversely related to the concentrations of L. monocytogenes in the broth. A calibration curve was obtained by plotting initial cell concentrations (CFU/mL) determined by conventional plate counting, as a function of the detection time. A linear response was found on the calibration curve for L. monocytogenes between 1 ∼ 9 times 10⁰ and 1 ∼ 9 times 10⁵ cells/mL. The detection time was approximately 17 and 6 h for 1 ∼ 9 times 10⁰ and 1 ∼ 9 × 10⁵ cells/mL of viable L. monocytogenes in the broth, respectively. The method was evaluated in detection of L. monocytogenes in milk samples.