The isoelectric point of bacteria as an indicator for the presence of cell surface polymers that inhibit adhesion

Abstract

The use of the isoelectric point (IEP) of a bacterium as a measure of the ability of bacterial surface polymers to inhibit adhesion was tested. This inhibition is attributed to repulsive steric interactions and not to electrostatic repulsion as accounted for by the DLVO theory of colloid stability. IEP values were compared with literature data on cell wall composition and with adhesion results, obtained at pH 7 and an ionic strength of 0.1 M. The literature data demonstrate that an IEP ⩽ 2.8 indicates the presence of significant amounts of cell surface polysaccharides containing negatively charged phosphate and/or carboxyl groups. The experimental results showed that these polymers inhibit adhesion onto both hydrophilic (glass) and hydrophobic (Teflon) surfaces. The coryneform Rhodococcus strain C125 with an IEP of 3.0 possesses amphiphilic cell surface components which inhibit adhesion onto glass and promote deposition onto Teflon. Bacteria with an IEP ⩾ 3.2 appear to be free from polymer coatings that inhibit adhesion. They adhere in large amounts onto Teflon and in slightly lower amounts onto glass. Our findings therefore indicate that the IEP is a suitable parameter complementary to hydrophobicity in predicting the affinity of bacterial surface polymers for substrata with different hydrophobicities.