Evaluation of the efficacy of antimicrobials against pathogens on food contact surfaces using a rapid microbial log reduction detection method

Microbial contamination of food contact surfaces in food processing industries is a significant health hazard. Evaluating the efficacy of sanitizing agents used during food processing is essential to ensure public health and safety. This study describes an optical screening method using an oCelloScope to quantify the number of surviving bacterial cells, expressed as microbial log reduction (MLR), after antimicrobial treatment. We tested the efficacy of two sanitizing agents, sodium hypochlorite and benzalkonium chloride, against desiccated cells of three pathogens, S. Enteritidis, E. coli O157: H7, and L. monocytogenes that are of concern on food processing surfaces. Stainless steel slides were used to mimic commercial food processing surfaces. Bacterial cells were desiccated at 75% relative humidity (RH) before antimicrobial treatment on stainless steel surfaces, and survivor levels were analyzed via plate counts to calculate MLR. These were compared to MLR values generated using the oCelloScope. For analysis of MLR using the oCelloScope, cells were desiccated at 75% RH on polystyrene microtiter plates, treated with antimicrobials, and surviving cell numbers were analyzed. Our results show that MLR values of treated desiccated cells calculated using the BCA algorithm of the oCelloScope were comparable to the values generated using the traditional plate count assay for the same concentration and treatment duration of the antimicrobials against all the tested pathogens. MLR could not be calculated for a non-lytic antimicrobial (curcumin and UV-A irradiation) against E. coli O157:H7, however, modified growth curves demonstrated an antimicrobial effect of curcumin and irradiation treatment. The results indicate that this method can be used for rapid screening of MLR of lytic antimicrobial compounds. Quantification of MLR using the oCelloScope is an effective tool to rapidly identify appropriate antimicrobial treatments and can be used to study novel antimicrobial compounds in the future.