| Summary: | 博士 === 國立臺灣師範大學 === 物理學系 === 103 === Visible femtosecond laser is shown to be capable of selectively inactivating a wide spectrum of microorganisms in a power density and pulse width dependent manner. However, the mechanism of how visible femtosecond laser affects the viability of bacteria is still elusive. In this thesis, the cellular surface properties, membrane integrity, metabolic rate and plasmid DNA conformation of Escherichia coli (E. coli) irradiated by a visible femtosecond laser with different power density and exposure time were investigated. Our results showed that femtosecond laser treatment for 60 minutes (min) led to cytoplasmic leakage, protein aggregation, and alternation of the physical properties of E. coli cell membrane. A power density dependent genetic damage from laser induced relaxation of supercoiled plasmid DNA was observed as well. In comparison, a 10 min exposure of bacteria to femtosecond laser irradiation induced an immediate reduction of 75% of the glucose-dependent respiratory rate, while the cytoplasmic leakage was not detected. Results from enzymatic assays showed that oxidase and dehydrogenases involving in E. coli respiratory chain exhibited divergent susceptibility after laser irradiation. This early commencement of respiratory inhibition after a short irradiation is presumed to play a dominant effect on the early stage of bacteria inactivation.
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