Antibacterial and Antibiofilm Effects of Photodynamic Treatment with Curcuma L. and Trans-Cinnamaldehyde against Listeria monocytogenes

Abstract

Photodynamic inactivation (PDI) is a highly effective treatment that can eliminate harmful microorganisms in a variety of settings. This study explored the efficacy of a curcumin-rich extract, Curcuma L., (Cur)- and essential oil component, trans-cinnamaldehyde, (Ca)-mediated PDI against Listeria monocytogenes ATCC 15313 (Lm) including planktonic cells and established biofilms on silicone rubber (Si), polytetrafluoroethylene (PTFE), stainless steel 316 (SS), and polyethylene terephthalate (PET). Applying Ca- and Cur-mediated PDI resulted in planktonic cell reductions of 2.7 and 6.4 log CFU/cm², respectively. Flow cytometric measurements (FCMs) coupled with CFDA/PI and TOTO^®-1 staining evidenced that Ca- doubled and Cur-mediated PDI quadrupled the cell damage. Moreover, the enzymatic activity of Lm cells was considerably reduced by Cur-mediated PDI, indicating its superior efficacy. Photosensitization also affected Lm biofilms, but their reduction did not exceed 3.7 log CFU/cm². Cur-mediated PDI effectively impaired cells on PET and PTFE, while Ca-mediated PDI caused no (TOTO^®-1) or only slight (PI) cell damage, sparing the activity of cells. In turn, applying Ca-mediate PDI to Si largely diminished the enzymatic activity in Lm. SS contained 20% dead cells, suggesting that SS itself impacts Lm viability. In addition, the efficacy of Ca-mediated PDI was enhanced on the SS, leading to increased damage to the cells. The weakened viability of Lm on Si and SS could be linked to unfavorable interactions with the surfaces, resulting in a better effect of Ca against Lm. In conclusion, Cur demonstrated excellent photosensitizing properties against Lm in both planktonic and biofilm states. The efficacy of Ca was lower than that of Cur. However, Ca bears potent antibiofilm effects, which vary depending on the surface on which Lm resides. Therefore, this study may help identify more effective plant-based compounds to combat L. monocytogenes in an environmentally sustainable manner.

Keywords: Curcuma L.; Listeria monocytogenes; biofilms; flow cytometry; photodynamic inactivation; trans-cinnamaldehyde.

Figure 1

Effect of photodynamic treatments at 234 J/cm² against Listeria monocytogenes ATCC 15313 planktonic cells and established biofilms on different surfaces, including silicone rubber (Si), polytetrafluoroethylene (PTFE), stainless steel 316 (SS), and polyethylene terephthalate (PET). Different letters indicate a significant difference within each culture variant (p < 0.05). BL− and BL+ represent the absence and the presence of blue light illumination. Ca and Cur stand for t-cinnamaldehyde and Curcuma L., respectively.

Figure 2

Cell number of Listeria monocytogenes ATCC 15313 planktonic cells (% of total; mean ± SD) in Curcuma L. (Cur)- and t-cinnamaldehyde (Ca)-based (non-)photosensitization experiments (BL−/BL+). Different bar colors indicate different cell subpopulations, as measured by FCM with CFDA/PI (left) and TOTO^®-1 staining (right). See Section 4.8 in Materials and Methods for details.

Figure 3

Cell number of Listeria monocytogenes ATCC 15313 cells (% of total; mean ± SD) on different surfaces, including silicone rubber (Si), polytetrafluoroethylene (PTFE), stainless steel 316 (SS), and polyethylene terephthalate (PET) in Curcuma L. (Cur)- and t-cinnamaldehyde (Ca)-based photosensitization experiments (BL+). CF−PI+ cells were labeled as experiencing damage (red bar) and CF+PI− as retaining activity (green bar). CF−PI− cells were labeled as non-active (white bar).

Figure 4

FCM dot plots of Listeria monocytogenes ATCC 15313 biofilms established on silicone rubber (Si), polytetrafluoroethylene (PTFE), stainless steel 316 (SS), and polyethylene terephthalate (PET) in Curcuma L. (Cur)- and t-cinnamaldehyde (Ca)-based photosensitization (BL+) experiments as measured by FCM with TOTO^®-1 staining.

Figure 5

The dissimilarity dendrogram among Lm assayed cells (a). The biplot of blue light (BL−/BL+), culture (P−planktonic cells and biofilms on PET, SS, PTFE, and Si), and photosensitization (Cur—Curcuma and Ca—t-cinnamaldehyde) variables related to PC1 and PC2 (b). The loading scatterplot (p1 vs. p2) illustrates clustering among the analyzed variables (c). The tested continuous variables include dead cells-PI, dead cells-TOTO^®-1, active, non-active, and culturable cells. The selected categorical variables were the culture (planktonic cells and biofilms on PET, SS, PTFE, and Si) and the treatment (BL+/BL−; Cur/Ca). The correlation coefficient (r) between differentially assayed cells measures their relationship strength (d). The correlation coefficients in bold are significant at a p < 0.05. 0—no linear relationship. 0.3—A weak relationship. 0.5—A moderate relationship. 0.7—A strong linear relationship.