Deposition of oral streptococci and polystyrene latices onto glass in a parallel plate flow cell

Abstract

Deposition of oral bacteria onto glass from a potassium phosphate buffered suspension has been studied in a parallel plate flow cell. Three bacterial strains with known surface free energies and zeta potentials, and two Strains (S. salivarius HB and S. salivarius HB‐C12) having well‐defined surface appendages have been employed. Polystyrene latices were included to provide a comparison with inert particles. Initial deposition rates of the various bacteria ranged from 0–1—2·9 × 10³ particles cm “"² sec”; ‘. The initial deposition rates have been related to an approximate theory of convective diffusion in which electrostatic interactions are omitted. A theory describing the influence of particle desorption and blocking on the deposition rate has been tested for its applicability to bacterial deposition at later stages. From the results it is concluded that a simple convective diffusion theory overestimates the experimental results, due to an increase in hydrodynamic friction of particles closely approaching the surface, which overbalances the attractive van der Waals forces. Deposition at later stages corresponded with theoretical expectations, from which a constant blocking of available adhesion sites on the surface can be concluded. Comparison of the deposition rates of particles experiencing an electrostatic potential barrier while approaching the substratum surface with those experiencing a net attractive force suggests that appendages present on the bacterial cell surface assist in deposition. Desorption is observed only during the first 5–10 seconds after deposition.