Xanthene Dyes and Green LED for the Inactivation of Foodborne Pathogens in Planktonic and Biofilm States

Abstract

This study evaluated the rose bengal‐ and erythrosine‐mediated photoinactivation against Salmonella Typhimurium and Staphylococcus aureus planktonic and sessile cells using green LED as a light source. The free‐living or 2‐day‐old biofilm cells were treated with different concentrations of the photosensitizing agents and subjected to irradiation. Only 5 min photosensitization with rose bengal at 25 nmol L−1 and 75 μmol L−1 completely eliminated S. aureus and S. Typhimurium planktonic cells, respectively. Erythrosine at 500 nmol L−1 and 5 min of light exposure also reduced S. aureus planktonic cells to undetectable levels. Eradication of S. aureus biofilms was achieved when 500 μmol L−1 of erythrosine or 250 μmol L−1 of rose bengal was combined with 30 min of irradiation. Scanning electron microscopy allowed the observation of morphological changes in planktonic cells and disruption of the biofilm architecture after photodynamic treatment. The overall data demonstrate that rose bengal and erythrosine activated by green LED may be a targeted strategy for controlling foodborne pathogens in both planktonic and sessile states.

The Remarkable Effect of Potassium Iodide in Eosin and Rose Bengal Photodynamic Action against Salmonella Typhimurium and Staphylococcus aureus

“…When we used KI at 50 mM, a half of the usual KI concentration, in combination with EOS or RB, a strong potentiate effect in the photoinactivation of S. Typhimurium and S. aureus is still observed, compared to the PSs alone [19,20] (Figure 3; p < 0.05). However, it was possible to observe that when EOS at 0.50 µM with KI at 50 mM was used, an additional time of light exposure of 10 min (9.0 J/cm 2 ) are needed, in comparison with the same EOS concentration with KI at 100 mM, to totally photoinactivate S. Typhimurium ( Figure 3A).…”

“…On the other hand, Bonin et al [19] used 5.0 µM of EOS alone to achieve the total inhibition of the bacterium at 5 min of light exposure. While Silva et al [20] reported that it was necessary to use 25 nM RB alone to achieve total inhibition of S. aureus cells with the same time of light exposure (5 min).…”

“…Then, the microorganisms were harvested by centrifugation (5000× g for 5 min) and washed three times with 0.85% saline solution. The inoculums were adjusted to approximately 1 × 10 7 colony-forming units (CFU) per mL and used in the experiments [20].…”

“…Importantly, these new methods should not induce the development of antimicrobial resistance [15][16][17]. Toward this end, antimicrobial photodynamic therapy (aPDT) has been considered as a promising non-antibiotic approach to inactivate foodborne bacteria [18][19][20][21][22][23].…”

“…Xanthene dyes have been considered good PSs to induce bacterial photoinactivation due to their low price, high molar absorptivity, and high singlet oxygen quantum yield (Φ ∆ ) [18,33,35]. The xanthene dyes, rose bengal (RB) and eosin Y (EOS) (Figure 1), have already proven to be effective against gram-positive and gram-negative bacteria [19,20,31,36], however, these dyes showed to be more effective against gram-positive bacteria. This limitation can be overcome by the use of different organic salts such as sodium bromide, sodium azide, sodium thiocyanate, and potassium iodide (KI) [36][37][38].…”