Antimicrobial Effect of Visible Light—Photoinactivation of Legionella rubrilucens by Irradiation at 450, 470, and 620 nm

Abstract

Despite the high number of legionella infections, there are currently no convincing preventive measures. Photoinactivation with visible light is a promising new approach and the photoinactivation sensitivity properties of planktonic Legionella rubrilucens to 450, 470, and 620 nm irradiation were thus investigated and compared to existing 405 nm inactivation data for obtaining information on responsible endogenous photosensitizers. Legionella were streaked on agar plates and irradiated with different doses by light emitting diodes (LEDs) of different visible wavelengths. When irradiating bacterial samples with blue light of 450 nm, a 5-log reduction could be achieved by applying a dose of 300 J cm−2, whereas at 470 nm, a comparable reduction required about 500 J cm−2. For red irradiation at 620 nm, no inactivation could be observed, even at 500 J cm−2. The declining photoinactivation sensitivity with an increasing wavelength is consistent with the assumption of porphyrins and flavins being among the relevant photosensitizers. These results were obtained for L. rubrilucens, but there is reason to believe that its inactivation behavior is similar to that of pathogenic legionella species. Therefore, this photoinactivation might lead to new future concepts for legionella reduction and prevention in technical applications or even on or inside the human body.

The in vitro Photoinactivation of Helicobacter pylori by a Novel LED-Based Device

“…This approach is particularly advantageous against bacteria naturally producing and accumulating endogenous photosensitizers such as porphyrins and flavins (Plavskii et al, 2018), physiologically involved in several essential biological functions (e.g., respiration, biological oxidation, photosynthesis, sulfate reduction, metabolism of fats, carbohydrates, and proteins) (Shu et al, 2013;García-Angulo, 2017;Sepúlveda Cisternas et al, 2018). Several studies determined the presence of endogenous photosensitizing porphyrins and/or flavins in Pseudomonas aeruginosa (Dai et al, 2013;Wang et al, 2016), Acinetobacter baumannii (Zhang et al, 2014;Wang et al, 2016), Candida albicans (Zhang et al, 2016), Aggregatibacter actinomycetemcomitans (Cieplik et al, 2014;Fyrestam et al, 2015), methicillin-resistant Staphylococcus aureus (Biener et al, 2017), Porphyromonas gingivalis (Fyrestam et al, 2015;Yoshida et al, 2017), Saccharomyces cerevisiae (Fyrestam et al, 2015;Hoenes et al, 2018), Legionella rubrilucens (Schmid et al, 2019), and Neisseria gonorrhoeae (Wang et al, 2019). The susceptibility to PDT has been demonstrated in Propionibacterium acnes, the etiological agent of acne, which produces porphyrins exploitable as photosensitizers (Romiti et al, 2000;Ashkenazi et al, 2003).…”

Visible Light as an Antimicrobial Strategy for Inactivation of Pseudomonas fluorescens and Staphylococcus epidermidis Biofilms

“…The number of photodynamic inactivation studies has greatly increased in recent years. These studies have mainly examined planktonic cells [38][39][40][41]43,[45][46][47][48][49][50][51][52], while few studies have taken bacterial biofilms into consideration [16,30,32,[50][51][52][53][54][55]. Since biofilms pose a major global healthcare problem, the impact of photodynamic inactivation on them is both crucial and innovative.…”

“…The findings of Section 2.5 also demonstrated that inactivation (light-killed population) of P. fluorescens biofilms was stronger than S. epidermidis biofilms when the total dose irradiating the samples was lower (2.5% and 25% I max , Figure 3 in Section 2.5). It can be conceivably hypothesized that the difference between P. fluorescens and S. epidermidis inactivation may be due to the presence of different endogenous PSs within each bacterial species having different absorption spectra [38][39][40][41]47]. Another reason may be the different quantity of PSs absorbing light per bacterial cell: a higher concentration leads to increased reactive oxygen species production and, therefore, a stronger killing effect under lower irradiation conditions.…”

“…Then, based on the literature that focused on the investigation of the endogenous PSs responsible for the photoinactivation and considering the absorption spectra of the porphyrins and flavins, it is possible to claim that the wavelengths with the strongest antibacterial effect are the ones belonging to the main absorption peak: violet-blue range [38][39][40][41]47]. Although the other wavelengths of the visible spectra followed in correspondence with the secondary absorption peaks of the same chromophores, they were harmless [38][39][40][41]47].…”

Photodynamic Therapy in the Inactivation of Microorganisms

“…These LED systems can also be used for obtaining information on responsible endogenous PSs. Microbial inactivation based on endogenous PSs is, at present, attracting increasing attention by the scientific community due to its intrinsic antimicrobial effect without the addition of exogenous PSs [8,[37][38][39]. The applicability of endogenous PSs for aPDT, as already observed when blue light therapy (aBLT) protocols are used, reduces the possibility of potential harmful effects on animal cells and also the impact in non-pathogenic microorganisms [8,39].…”