Electrochemical biosensor for timely detection of Lactococcus lactis bacteriophage in milk samples

Milk contaminations by Lactococcus lactis bacteriophages prevent the proper lactic fermentation, causing large economic losses in the dairy industry. This work presents a novel cost-effective biosensor for monitoring the presence of L. lactis phages in milk samples in less than 4 hours. The detection relies on the parametric variations in the electrochemical impedance spectroscopy response of the proposed biosensor. Differences of more than one order of magnitude is measured in the charge transfer resistance when the solution under test is contaminated by phages, due to the phage lytic activity on the L. lactis bacteria. The sensing approach is validated in milk samples by comparing the proposed electrochemical sensing with the optical absorbance of the solutions at 600 nm. Finally, the biosensor performance is improved by treating the milk samples with calcium chloride which enhances the phage activity, thus leading to larger shifts in the charge transfer resistance. Tests at different phage concentrations reveal minimum detecting capabilities of 105 PFU/mL of phages in milk.