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.
Highlights
Legionella species are widely distributed in natural and artificial water systems, such as lakes, rivers, building water distribution networks, and cooling towers, and any system producing aerosolized water represents a potential origin of legionellosis [1,2].By inhaling aerosols of water contaminated with legionella, they can cause Pontiac fever or even lethal pneumonia
The observed deviation of the exponential bacterial reduction for lower irradiation doses in Figure 3, the so-called “shoulder”, and its wavelength dependence, are in good agreement with the photoinactivation literature results presented for other microorganisms
Webb et al, described a similar increase of the shoulder effect with an increasing wavelength for experiments with Escherichia coli [30]. They formulated the hypothesis that the shoulder effect itself could be explained by dose-dependent repair processes and that the repair processes would become insufficient with increasing doses [30]
Summary
Legionella species are widely distributed in natural and artificial water systems, such as lakes, rivers, building water distribution networks, and cooling towers, and any system producing aerosolized water represents a potential origin of legionellosis [1,2].By inhaling aerosols of water contaminated with legionella, they can cause Pontiac fever or even lethal pneumonia. Legionella species are widely distributed in natural and artificial water systems, such as lakes, rivers, building water distribution networks, and cooling towers, and any system producing aerosolized water represents a potential origin of legionellosis [1,2]. Suspected sources of legionella infections relevant to humans are, e.g., showers or cooling water reservoirs, and dental instruments or flushing toilets that produce water aerosols [5,6]. For the prevention of legionella infections, many conventional disinfection procedures are possible: chlorine and ozone treatment or thermal disinfection. These measures are similar in that they all entail various disadvantages, such as the generation of toxic byproducts or high-energy consumption
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