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Legionella pneumophila is ubiquitous in natural and anthropogenic water systems, in which it is able to survive for long periods within biofilms or within various free-living amoebae. In order to restrain L. pneumophila growth, various water systems treatments are used (e.g., physical, thermal, and chemical). The problem is that this opportunistic premise plumbing pathogen often survive standard disinfection and is not washed out of pipes because of biofilm-formation and survival within free-living amoebae. It is therefore necessary to explore new methods for destroying Legionella in biofilm and within amoeba. The aim of this work is to propose two new approaches in controlling Legionella infections. One approach is the use of natural substances such as essential oils (individually or in combination) and another approach is photodynamic therapy (PDT) of microorganisms using synthetic dyes and porphyrins. In our research the interaction of different essential oils from the coastal region of Croatia were tested. For various combinations of essential oils, we have proved to have a synergistic effect on planktonic and sessile bacteria in biofilm. Photodynamic therapy (PDT), based on cytotoxic action of singlet oxygen and other reactive oxygen species (ROS), produced upon the visible light-excitation of a photosensitizer (PS), showed complete inactivation of Legionella in sterile tap water in very low concentration of 0.024 µM. The photosensitizer uptake assay has shown that this PS binds to the bacterial cell, already after 10 minutes of incubation in the dark. To conclude, EO and other natural anti-Legionella molecules described could provide new eco- friendly and alternative ways to struggle against this important pathogen in plumbing and could be used in hot water systems like baths, spa pools, hot tubs, or even foot baths/whirlpools. Photodynamic therapy shows very good potential and could be used in treatment of technological and waste water systems. |
