Activity of chlorhexidine against Escherichiacoli growing as biofilms on inert solid phase

Abstract

Bacterial adhesion is important in ecology as well as in biotechnology. In medicine, bacterial adhesion to solid surfaces plays a significant role in the development of implant- or catheter-related infections. In the laboratory, bacteria are generally cultivated and studied as cell suspensions in liquid media. The natural environment, however, is more complex. It has been reported in a number of studies that bacteria growing in biofilms are more resistant to biocides than those grown in culture. The present study investigated the colonization of an inert solid phase Tygon ® in an original system with Escherichia coli ATCC 10 536, in a continuous flow of fresh medium under iron-limiting conditions and sufficiently diluted to preclude the growth of suspended cells. The bactericidal activity of chlorhexidine was examined against biofilms established under dynamic conditions, and was compared for the same strain in suspension, in compliance with AFNOR NFT 72–170 (static conditions). The adhering cells and the suspended cells in the eluates were evaluated by viable counts after 1, 2, 3, 4 and 5 days. The results of this study suggested that cells in biofilms were more susceptible to chlorhexidine than suspended cells. According to this model, the biofilms were less susceptible under dynamic conditions than under static conditions (AFNOR). The activity of chlorhexidine at the concentration normally used for bladder washouts (200 μg ml −1) against Escherichia coli was discussed.