Browsing by Author "Yoon, Jeyong"

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Comparison of antimicrobial effect on biofilm of chlorine, silver ion and tobramycin
(2008-01) Kim, Jaeeun; Pitts, Betsey; Stewart, Philip S.; Camper, Anne K.; Yoon, Jeyong
The systematic understanding of how various antimicrobial agents are involved in controlling biofilm is essential in order to establish an effective strategy for biofilm control, since many antimicrobial agents are effective against planktonic cells but ineffective when used against the same bacteria growing in a biofilm state. Three different antimicrobial agents (chlorine, silver, and tobramycin) and three different measures of efficacy were selected to examine antimicrobial activity on biofilm in a comparative way: plate counts, measurement of respiratory activity with CTC staining, and BacLight Live/Dead stain for measuring membrane integrity were used along with CLSM and epifluorescence microscopy. The three methods of determining antimicrobial activity gave very different results for each antimicrobial agent. Tobramycin appears to be the most effective in reducing the respiratory activity of biofilm cells compared to chlorine and silver, based upon CTC staining. In contrast, tobramycin-treated biofilm cells maintained membrane integrity better than chlorine or silver treated ones, evidenced by both CLSM and epifluorescence microscope imaging. Combined and sequential treatments with silver and tobramycin showed an enhanced antimicrobial efficiency of more than 200%, while the antimicrobial activity of either chlorine or tobramycin was antagonized when the agents were used in combination. This observation makes sense when the differing oxidative reactivities of chlorine, silver and tobramycin are considered.
Tolerance of dormant and active cells in Pseudomonas aeruginosa PA01 biofilm to antimicrobial agents
(2008-10) Kim, Jaeeun; Hahn, Ji-Sook; Franklin, Michael J.; Stewart, Philip S.; Yoon, Jeyong
Objectives: The aim of the study was to determine the susceptibility of active and dormant cell populations from Pseudomonas aeruginosa biofilms to non-antibiotic antimicrobial agents such as chlorine, hydrogen peroxide and silver ions in comparison with antibiotics. Methods: Active cells in colony biofilm were differentially labelled by induction of a green fluorescent protein (GFP). Active and dormant cells were sorted in phosphate buffered solution by flow cytometry. Reductions in viability were determined with plate counts. Results: The spatial pattern of metabolic activity in colony biofilm was verified, and the active and dormant cells were successfully sorted according to the GFP intensity. Active cells had bigger cell size and higher intracellular density than dormant cells. While dormant cells were more tolerant to tobramycin and silver ions, active cells were more tolerant to chlorine. Metabolically active cells contain denser intracellular components that can react with highly reactive oxidants such as chlorine, thereby reducing the available concentrations of chlorine. In contrast, the concentrations of silver ions and hydrogen peroxide were constant during treatment. Aerobically grown stationary cells were significantly more tolerant to chlorine unlike other antimicrobial agents. Conclusions: Chlorine was more effective in inactivation of metabolically inactive dormant cells and also more effective under anaerobic conditions. The high oxidative reactivity and rapid decay of chlorine might influence the different antimicrobial actions of chlorine compared with antibiotics. This study contributes to understanding the effects of dormancy and the presence of oxygen on the susceptibility of P. aeruginosa biofilm to a wide range of antimicrobial agents.