Comparison of antimicrobial effect on biofilm of chlorine, silver ion and tobramycin

Abstract

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.