Decreased susceptibility of Serratia marcescens to chlorhexidine related to the inner membrane.

An isolate of Serratia marcescens (strain 100) obtained from a handwashing solution of chlorhexidine (Hibitane) was found not to release potassium ions when exposed to chlorhexidine as compared to chlorhexidine susceptible clinical isolates of Escherichia coli and Ser. marcescens. Lysozyme-tris-EDTA spheroplast preparations of the Serratia isolates were also tested for potassium ion leakage following exposure to chlorhexidine and it was found that the inner membrane was responsible for the decreased susceptibility of the organism of chlorhexidine. These experiments suggested that the mechanism of increased resistance of strain 100 Ser. marcescens to chlorhexidine was an inner membrane change. The nature of the change is currently unknown.