Effects of shear on initial bacterial attachment in slow flowing systems

Initial bacterial attachment, likely affected by local shear, could influence biofilm formation. However, there are contradictory reports for the shear effects on attachment of different bacteria onto different surfaces. In this study, four bacteria, Staphylococcus epidermidis, Pseudomonas aeruginosa, Pseudomonas putida, and Escherichia coli, were examined for their attachment to glass and octadecyltrichlorosilane (OTS) modified glass under different shears. Polystyrene particles were used to verify that their shear dependent attachment on glass and OTS could be interpreted using an analysis based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. In particular, the critical shear force (F(c-shear)) could correlate with the maximum attractive force (F(MAX)(XDLVO)) toward the secondary energy minimum as F(c-shear)=cF(MAX)(XDLVO). For these particles, c of ~1 was obtained, the value was within the coefficient range (0.1-1) of substances sliding over glass. For S. epidermidis, E. coli and P. aeruginosa on glass, c was 0.3, <0.6 and 0.2, respectively. When considering potential protein adsorption on OTS during bacterial attachment, c of these species on OTS was slightly above 1. A greatly enhanced attachment of P. aeruginosa on OTS was also observed, probably due to the presence of flagella. For P. putida, the attachment first decreased slightly or maintained with shear and then increased. Such behaviors were probably caused by the increased secretion of extracellular polymeric substances (EPS) at higher shears by P. putida. The results from this study suggested that, without complications from surface features/EPS, the analysis based on the XDLVO theory could provide a basis for understanding shear effect on initial bacterial attachment.