Relationship Between Cell Surface Hydrophobicity and Biofilm Adhesion in Opportunistic Serratia Species with Disparate Susceptivity to Triclosan Sensitization

We have recently reported that ten opportunistically pathogenic Serratia species markedly
differ regarding susceptivity to sensitization to the hydrophobic biocide triclosan by outer membrane permeabilization. Representative organisms exhibiting slight (Serratia marcescens), complete (Serratia fonticola), transitorily complete (Serratia liquefaciens), and intermediate (Serratia rubidaea) susceptivity were selected for further analysis. The purpose of the present study was to determine if such phenotypic susceptivity is related to cell surface hydrophobicity properties and the proclivity to implement biofilm adhesion. Hydrocarbon adherence and hydrophobic fluorescent probe assays were employed to quantitate cell surface hydrophobicity properties, while an in vitro biofilm assay was used to assess adhesion of planktonic cells to a nonpolar substrate. While S. rubidaea was seen to be extremely hydrophobic, S. marcescens and S. liquefaciens were slightly to moderately hydrophobic,
and S. fonticola was relatively hydrophilic. S. rubidaea adhered to the polystyrene substrate more readily than S. fonticola or S. liquefaciens, while S. marcescens adhesion was intermediate. These data do not support the notion that the degree of susceptivity to triclosan sensitization by outer membrane permeabilization is directly related to cell surface hydrophobicity. However, the initial adhesion stage of biofilm formation appears to be influenced at least in part by cell surface hydrophobicity properties.