Inactivation of Legionella pneumophila by cinnamaldehyde
Date Issued
2010
Date
2010
Author(s)
Chang, Fang-Tzu
Abstract
Cinnamaldehyde is a major component in mature leaves of Cinnamomum osmophloeum. It has been proved to inactive planktonic Legionella pneumophila, an organism causing Legionnaires’ disease and Pontiac fever. L. pneumophila usually survives in water environment as habitants, living within biofilms that commonly found in distribution systems and cooling towers. Bacteria in biofilms are generally considered to be more resistant against disinfectants, and detachment of biofilm cells becomes a continual source providing microbial contamination to the bulk water. There was no research focused on the disinfection efficiency of L. pneumophila biofilms by cinnamaldehyde, and fewer studies focused on the effect of pH value and temperature on cinnamaldehyde’s effect on sessile cells. Therefore, the purpose of the study was to investigate the antibacterial effect of cinnamaldehyde against sessile L. pneumophila which were in static and continuous-flow culture, and to evaluate the pH and temperature effects on the disinfection efficacy of cinnamaldehyde on sessile L. pneumophila. In addition to observing the effect of cinnamaldehyde on cellular culturability by culture assay, ethidium monoazide coupled with real-time quantitative PCR (EMA-qPCR) was used to observe the effect of cinnamaldehdye on cell membrane integrity. The results shows that cinnamaldehyde was effective in disinfection of sessile L. pneumophila, and the antibacterial effect increased with the concentration and contact time (P<0.05), indicating a dose-response biocidal effect against sessile L. pneumophila. Contacted with cinnamaldehyde at concentration higher than 1000 μg/ml for 60 min, sessile L. pneumophila totally lost their culturability on BCYEα agar. Expose to 125 μg/ml of cinnamaldehyde for 10 min, cell membrane damage measured by EMA-qPCR assay was observed. The inactivation rate was 10.25% for static cultured bilfilms and 7.37% for continuous-flow culured biofilms. However, the susceptibility to cinnamaldehyde at concentration lower than 500 μg/ml was significantly different between two kinds of sessile cells (P<0.05). The different structure of two kinds of sessile cells was further proved by confocal laser scanning microscopy (CLSM), supporting that different structural feature between two kinds of sessile cells may contribute to different susceptibility to cinnamaldehyde. Moreover, the disinfection efficacy was enhanced against sessile cells at higher pH levels and at higher temperatures.
In conclusion, in this study, it was found that cinnamaldehyde is an effective disinfectant not only against planktonic L. pneumophila but also sessile L. pneumophila by destroying their cell membrane or cellular culturability. In the future, cinnamaldehyde possesses the potential to be used to control Legionella in aquatic environment with high pH values and high temperature, e.g., air-conditioning cooling towers in the summer.
Subjects
L. pneumophila
biofilms
cinnamaldehyde
pH effect
temperature effect
Type
thesis
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