November 26, 2024 - Margarita Valdiviezo, M.Sc. Ph.D. Candidate, Alcaine Lab, Cornell University

Ph.D. Candidate, Alcaine Lab (https://cals.cornell.edu/samuel-david-alcaine)

Department of Food Science

Cornell University

Antimicrobial Systems Effective against Spore-Forming Bacteria and Food Pathogens

Abstract

The lactoperoxidase system (LPS) is a natural antimicrobial system present in milk. LPS is activated in the presence of H2O2, which is produced during the oxidation of lactose to lactobionic acid by lactose oxidase (LO). The application of LO to improve the efficacy of the LPS and inhibit microbial growth is an approach that can be used to extend the shelf lives of dairy products. The first study evaluated the antimicrobial effects of LO in the LPS against 28 strains of spore formers isolated from dairy products and facilities, and determined the concentration effective for growth inhibition through an overlay assay. Results indicated that 15 out of the 28 strains were inhibited by the lowest LO concentration (0.1 g/L); 10 additional strains experienced inhibition at 1 g/L; and the 3 remaining strains (Bacillus subtilis, B. paralicheniformis, and B. gibsonii) were inhibited only at the highest LO concentration of 10 g/L. A second study assessed the efficacy of hydrogen peroxide (HP); phosphoric acid (PA); or a commercial sanitizer (CS) containing HP, peracetic acid, and acetic acid, as sanitizer alternatives to chlorine, suitable for reducing the growth of dairy spore formers on common work surfaces. For this aim, the selected sanitizers were tested according to the AOAC Method 2008.05, which simulates three different mechanisms of bacterial removal and assesses the remaining bacterial load after each. Results indicated that only HP proved to be effective against all the spore strains tested, with reductions of at least 4 log units on PVC, 4 logs on stainless steel, and 3 logs on rubber coupons, respectively. Neither PA nor CS achieved more than a 1 log-unit reduction of spores on any of the same surfaces. Nevertheless, these applications presented side effects such as target ambiguity and possible changes in nutritional and sensory attributes, due to a high concentration of HP or acid. Therefore, in a third study, specific antibody-oxidase conjugates were synthesized, and their inhibition potentials against target pathogens were assessed in comparison to those of unconjugated sugar oxidases. For this aim, a sugar oxidase was conjugated to an antibody specific for Listeria monocytogenes and was added to a culture of 2 log CFU/ml. Results indicated that the inhibition potential was higher when both antibody and enzyme were present. However, further studies are being carried out to evaluate the effects on the enzyme activity and the target specificity of the conjugates. In conclusion, conjugates of antibody-sugar oxidases represent promising food-safety tools that can potentially target specific food pathogens with minimal secondary effects. These tools could provide novel methods to control food pathogens and spore-forming bacteria in dairy environments.