Activity of antiseptics against Escherichia coli growing as biofilms on silicone surfaces

The activity of chlorhexidine, acetic, lactic and mandelic acids were examined against biofilms of Escherichia coli established on silicone discs and against the test strain growing in suspension in urine. The results showed that the concentrations of chlorhexidine and acetic acid normally used for bladder instillations to control infections in patients with indwelling catheters failed to eliminate cells from the biofilm in exposure periods of up to 2 h. Lactic acid (1% v/v) had a bactericidal effect on planktonic cells but poor activity against cells in the biofilm. Mandelic acid (1% v/v), and mandelic (1% v/v) and lactic acid (1% v/v) mixtures eliminated organisms from both suspensions and biofilms. It is suggested that these solutions be considered as alternatives to acetic acid and chlorhexidine for the washing of catheterized bladders.