Shining a light on Salmonella enterica: Chlorophyllin and Chitosan
Foodborne illness is a common occurrence around the world. The World Health Organization (WHO) states that 1 in 10 people worldwide fall ill from contaminated food each year (1). In the United States, about 1 in 6 people (48 million) contract a foodborne illness from contaminated food, costing roughly $365 million in medical costs each year (2).
Over 200 diseases are caused by eating contaminated food and can occur at any stage of food production, delivery, and consumption chain. Food can be contaminated with bacteria, viruses, parasites, or chemical substances such as heavy metals (1). A common bacteria responsible for causing foodborne illness is Salmonella. In the U.S., around 1 million cases of Salmonella are diagnosed every year (3). Salmonella can be found in a variety of foods including beef, chicken, eggs, fruits, pork, sprouts, vegetables, and even processed foods, such as nut butters, frozen pot pies, chicken nuggets, and stuffed chicken entrees (3). Due to its commonality and significant social and economic impact, it’s important for researchers to continue seeking out new and effective solutions to combat Salmonella and other foodborne illnesses.
The main objective of this in vitro study focused on inactivating Salmonella (S.) enterica after it was treated with a chlorophyllin and chitosan complex and visible light. Previous studies have used similar treatment methods for the decontamination of fresh produce and food-related surfaces (4-6). One additional study has documented photosensitization, through photodynamic therapy, as a cure for cancer and infectious diseases (7). Rodríguez- López, et al. evaluated the inactivation of S. enterica treated with photoactivated chlorophyllin-chitosan complex and predicted the possible regrowth of the bacterium after the treatment (8).
Rodríguez- López, et al. incubated Salmonella cells with 0.001% chlorophyllin and 0.1% chitosan (chlorophyllin-chitosan complex) for different amounts of time (ranging from 5-60 min) and then illuminated with an LED-based light source from both sides. They felt it was interesting to note that chlorophyllin can act as an effective photosensitizer. According to ScienceDirect, photosensitizers are molecules that can be activated by light to produce ROS (reactive oxygen species) which can damage cell structures from microorganisms (such as bacteria, viruses, and fungi) or from “diseased mammalian cells” causing the death of the diseased cells (9).
In this study, there were both advantages and disadvantages to photosensitization. The main advantage was is efficacy against a wide range of microorganisms: Gram-positive and Gram-negative bacteria, their vegetative forms and spores, and fungi and yeasts. Also, the treatment is environmentally friendly and cost-effective, which saves both water and energy. However, there was an important disadvantage to the treatment. The susceptibility of Gram-negative bacteria to photosensitization using this method is lower than that of Gram-positive bacteria. This disadvantage prompted the researchers to combine chlorophyllin-based photosensitization with other antimicrobials (8). Thus, the addition of chitosan.
Chitosan is a food additive derived from chitin. Chitin is found in the exoskeletons of insects, the cell walls of fungi, and certain hard structures in invertebrates and fish. It is often used in medicines and nutritional supplements (10). Chitosan has been used to help control body mass and blood pressure and is also a likely effective treatment for high cholesterol and wound healing (11).
Researchers divided the treatments into five groups:
1) Control (no sensitizer, no illumination)
2) Chitosan, no illumination
3) Photoactivated chlorophyllin
4) Chlorophyllin-chitosan complex, no illumination
5) Photoactivated chlorophyllin-chitosan complex
Results from the study showed that treatments with photoactivated chlorophyllin-chitosan complex (fifth treatment group) caused significant inactivation of S. enterica compared to the other four treatment groups. Photoactivated chlorophyllin alone (third group) also showed some inactivation, although not as much as the photoactivated chlorophyllin-chitosan complex group (8).
Even with excellent inactivation results, it is important to evaluate the microbial inactivation and the regrowth of the surviving microorganism population. The initial microbial inactivation can render food safe and stable but surviving microorganisms can grow during food storage, posing a threat to their safety and stability. The researchers observed that “treatment with photoactivated chlorophyllin-chitosan complex caused damage to S. enterica population that made it impossible to regrow during the first 15 hours after the treatment (8).”
Read the full study here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7365337/
(1) Foodborne diseases. (2020). World Health Organization. https://www.who.int/health-topics/foodborne-diseases#tab=tab_1
(2) Making Food Safer to Eat. (June 2011). Centers for Disease Control and Prevention. https://www.cdc.gov/VitalSigns/foodsafety/
(3) Salmonella and Food. (July 9, 2020). Centers for Disease Control and Prevention. https://www.cdc.gov/foodsafety/communication/salmonella-food.html
(4) Luksiene, Z., Paskeviciute, E. (2011). Novel approach to the microbial decontamination of strawberries: Chlorophyllin-based photosensitization. Journal of Applied Microbiology. 110(5), 1274-1283. https://doi.org/10.1111/j.1365-2672.2011.04986.x
(5) Buchovec, I., Lukseviciute, V., Marsalka, A., Reklaitis, I., Luksiene, Z. (2016). Effective photosensitization-based inactivation of Gram (−) food pathogens and molds using the chlorophyllin-chitosan complex: Towards photoactive edible coatings to preserve strawberries. Photochemical & Photobiological Sciences. 15(4), 506-516. https://doi.org/10.1039/c5pp00376h
(6) Paskeviciute E., Zudyte, B., Luksiene, Z. (2018). Towards better microbial safety of fresh produce: Chlorophyllin-based photosensitization for microbial control of foodborne pathogens on cherry tomatoes. Journal of Photochemistry & Photobiology B: Biology. 182, 130-136. https://doi.org/10.1016/j.jphotobiol.2018.04.009
(7) Wainwright, M. (1998). Photodynamic antimicrobial chemotherapy. Journal of Antimicrobial Chemotherapy. 42(1), 13-28. https://doi.org/10.1093/jac/42.1.13
(8) Rodríguez- López, M., Gómez-López, V., Lukseviciute, V., Luksiene, Z. (2020). Modelling the Inactivation and Possible Regrowth of Salmonella enterica Treated with Chlorophyllin-Chitosan Complex and Visible Light. Food Technology & Biotechnology. 58(1), 64-70. https://doi.org/10.17113/ftb.58.01.20.6374
(9) Photosensitizers. (2020). ScienceDirect. https://www.sciencedirect.com/topics/materials-science/photosensitizers
(10) Chitin. (April 28, 2017). Biology Dictionary. https://biologydictionary.net/chitin/
(11) Health Library: Chitosan. (2020). Winchester Hospital. https://www.winchesterhospital.org/health-library/article?id=21656