PHOTODYNAMIC INACTIVATION
of Food Borne & Spoilage Bacteria Microbial contamination of foods continues to be a major concern for public health, consumers, regulatory agencies and food industries throughout the world. Foodborne pathogens are responsible for numerous illnesses, which affect thousands of people, mostly children, pregnant women, babies, the elderly and people with vulnerable diseases, and can lead to death in many cases (WHO, 2015). The Center for Disease Control and Prevention (CDC) estimates that 48 million people become ill and 3.000 die due to foodborne diseases (CDC, 2015). Spoilage bacteria cause food losses, with a significant economic, social and environmental impact (Lipinski et al., 2013).
Among the strategies used to ensure microbiological safety and food preservation are the use of chemical preservatives, thermal processes, such as pasteurization, other physical methods such as dehydration and irradiation, and new preservation treatments such as high hydrostatic pressure (Gonzalez & Barret, 2010).
Photodynamic inactivation (PDI) is a new and promising strategy to eradicate microorganisms such as Gram positive and Gram-negative bacteria, yeasts, molds, viruses and parasites (Alves et al., 2015). This technique is based on the use of photosensitizers (PSs) activated by an appropriate wavelength light (Jiang, Leung, Hua, Rao, & Xu, 2014). Several light sources such as lasers, LEDs halogen lamps are currently used (Nagata et al., 2012). LEDs have been used as alternative light sources due to their low cost, wider emission bands, ease of use and greater flexibility in irradiation time (Costa et al., 2011).
The toxicity of PDI comprises the drug excitation phases, encouraging the production of reactive oxygen species (ROS) and leads to cell death (Alisson, Moat, Bagnet, & Sibata, 2008; Chatterjee, Fong, & Zhang, 2008). This free radical hinders microbial resistance as it interacts in many cell structures such as lipid membranes, proteins and nucleid acids (Konopka & Goslinski, 2007).
The advantages of PDI are that no toxic chemicals are generated, the only energy required is the light source, there is a low probability of triggering the development of resistance in microorganisms and it can be potential applied in several areas: hospital, dental, industrial and environmental (Alves et al., 2015; Luksiene & Brovko, 2013).
Different PSs, including porphyrins, phthalocyanines, chlorophyllin and xanthene dyes have been tested against microorganisms. These are fundamentally defined as agents that produce singlet oxygen following light stimulation (Alisson, Mota, Bagnet, & Sibata, 2008). Among naturally occurring PSs, curcumin is a yellow pigment isolated from Curcuma longa (Soria-Lozano et al., 2015), and has been used as a spice since ancient times (Rao & Khanum, 2016). Among its many biological activities are its anti- oxidant (Rao & Khanum, 2016; Singh et al., 2010), antimicrobial (Arutselvi, Balasaravanan, Ponmurugan, Saranji, & Suresh, 2012), anti-HIV (Rao & Khanum, 2016) anti-inflammatory and anticancer (Sharma, Gescher, & Steward, 2005) properties. Curcumin absorbs blue light in an absorption spectrum range of 400e500 nm, and it can be used as a potential natural photosensitizer (Jiang et al., 2014;Soria-Lozano et al., 2015).
The use of curcumin-mediated photosensitization has been re- ported against a range of bacteria and fungi, such as Staphylococcus aureus (Jiang et al., 2014), Staphylococcus epidermidis (Hegge, Bruzell, Kristensen, & Tønnesen, 2012) Enterococcus faecalis (Frota et al., 2015; Haukvik, Bruzell, Kristensen, & Tønnesen, 2009), Streptococcus mutans (Manoil et al., 2014; Paschoal et al., 2013; Soria-Lozano et al., 2015), Streptococcus intermedius (Haukvik et al., 2009) Lactobacillus spp. (Bulit et al., 2014), Escherichia coli (Haukvik et al., 2009), Candida spp. (Andrade et al., 2013; Dovigo et al., 2011; Soria-Lozano et al., 2015). and Aspergillus flavus (Temba, Fletcher, Fox, Harvey, & Sultanbawa, 2016). Thus, the aim of this study was to evaluate antimicrobial photodynamic activity in vitro against pathogenic and spoilage bacteria using curcumin as a photosensitizer.
The present study evaluated the efficacy of photodynamic inactivation (PDI) of foodborne and spoilage bacteria using curcumin and a light emitting diode (LED).
Curcumin at 75 mM was used to photo- irradiate Staphylococcus aureus ATCC 25923, Aeromonas hydrophila ATCC 7966, Salmonella Typhimu- rium ATCC 14028, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 at light doses of 139 J/cm2, 278 J/cm2 and 417 J/cm2.
The cytotoxicity of curcumin in VERO cells was evaluated in similar conditions to bacterial photoinactivation assay, and the percentage of cell destruction was y 13 ± 0.05%, for all light doses.
Curcumin-mediated PDI of S. aureus induced a significant reduction of approximately 3.50 log CFU/ml at 139 J/cm2 and 278 J/cm2.
Full inactivation was observed at 417 J/cm2.
Among Gram negative bacteria, P. aeruginosa was the least susceptible to PDI, which counts were not significantly reduced.
A significant reduction in E. coli counts was observed at 278 J/cm2, and no viable cells were detected after light exposure at 417 J/cm2.
When photo-irradiated with curcumin at 278 J/cm2 and 417 J/ cm2, A. hydrophila was completely eradicated, while a significant decrease (3.33log CFU/ml) was observed in bacterial counts at 139 J/cm2.
Curcumin in combination with RAYPURE* LED is a potential candidate for PDI against Gram positive and Gram-negative bacteria.
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*RAYPURE specifically made for PDI application
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