Researcher's Profile

CHING-WEN CHANG (張靜文)

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Research Outline      2015-03-17 12:17:38

Dr. Chang’s research themes focus on environmental pathogenic microorganisms with a perspective of biological hazard prevention. There are two major categories in Dr. Chang’s researches: (1) development of environmental monitoring techniques and (2) evaluation of control measures, with Legionella, Acanthamoeba, Hartmannella, Staphylococcus aureus, Pseudomonas aeruginosa, total fungi and bacteria as study subjects.

In terms of the development of environmental monitoring techniques, the first part of her researches emphasized on the methodology for identifying and quantifying Legionella in water, biofilm, and air as Legionella spp. are often present in water and biofilm and may cause legionellosis in humans via air transmission. Considering the fact that accurate quantification of environmental Legionella is problematic due to its fastidious nature by culture assay, molecular techniques were adopted in Dr. Chang’s studies. Major research achievements included: (1) optimization of the methods for DNA isolation and elimination of polymerase chain reaction (PCR) inhibition caused by humic acid and ferric ion; (2) development of rapid quantification method for viable legionellae using ethidium monoazide (EMA) coupled with real-time quantitative PCR (qPCR); and (3) determination of the most appropriate sampling methods for quantifying culturable, viable, and total Legionella in air.

For the second part of Dr. Chang’s researches on monitoring techniques, she emphasized on the development of qPCR-based methodology for quantification of Acanthamoeba trophozoites and cysts, which are the natural hosts of many waterborne pathogens (e.g., Legionella and Mycobacterium) and may cause keratitis and lethal encephalitis in humans. Major research achievements in this part included: (1) optimization of the procedures for DNA extraction and minimization of PCR inhibitors via laboratory and field evaluations; (2) determination of the optimal qPCR method to quantify environmental Acanthamoeba; and (3) development of the qPCR-based methodology to quantify viable trophozoites and cysts of Acanthamoeba, and verification of the developed technique using Acanthamoeba preheated at different temperatures.   

With the established monitoring techniques, Dr. Chang continuously moved forward her works into the exposure assessment of environmental Legionella and Acanthamoeba, including monitoring the abundance of Legionella and Acanthamoeba in cooling towers and hot water systems of nursing homes and in biological aeration basins of wastewater treatment plants. Significant environmental factors affecting the distribution of Acanthamoeba and the influence of amoebic density on the population of Legionella have also being assessed. In addition, Dr. Chang persistently conducted exposure assessment studies on environmental and occupational biohazards, e.g., bacteria and/or fungi exposure in hospitals, farmlands and the International Taipei Flora Exposition.

With respect to the evaluation of control measures against environmental pathogens, the major research achievements included: (1) characterization of the responses of Legionella in face with conventional disinfection treatment—illustrating that long-term starved L. pneumophila may resist against superheating and chlorination evident by presence of abundant cells with intact membrane, and that L. pneumophila replicated from Hartmannella vermiformis possess greater chlorine resistance than the cells from Acanthamoeba castellanii, which findings provide possible explanations for re-colonization of legionellae observed in the systems following superheating and/or chlorination; (2) exploration of novel disinfectants against legionellae—verifying that the essential oil extracted from Cinnamomum osmophloeum leaves of cinnamaldehyde type possesses strong bactericidal effect against legionellae and remains effective in spring water with various conductivity and pH levels; and (3) evaluation of the effectiveness of ultraviolet germicidal irradiation (UVGI) against airborne pathogens—demonstrating that the UVGI effectiveness is significantly influenced by relative humidity and the susceptibility to UVGI is quite different among airborne S. aureus, P. aeruginosa and L. pneumophila.