Stochasticity of bacterial attachment and its predictability by the extended Derjaguin-Landau-Verwey-Overbeek Theory

ABSTRACT Bacterial attachment onto materials has been suggested to be stochastic by some authors but non-stochastic and based on surface properties by others. We investigated this by attaching pair-wise combinations of two Salmonella Sofia (S. Sofia) strains (with different physicochemical and attachment properties) with one strain each of Salmonella Typhimurium, Salmonella Infantis or Salmonella Virchow (all with similar physicochemical and attachment ability) in ratios of 0.428, 1 and 2.333 onto glass, stainless steel, Teflon® and polysulfone. Attached bacterial cells were recovered and counted. If the ratio of attached cells of each Salmonella serovar pair recovered was the same as the initialinoculum ratio, the attachment process was deemed stochastic. Experimental outcomes from the study were compared to those predicted by the “extended” Derjaguin-Landau- Verwey-Overbeek (XDLVO) theory. Significant differences (P<0.05) between the initial and the attached ratios for serovar pairs containing S. Sofia S1296a for all different ratios were apparent for all materials. For S. Sofia S1635 containing pairs, seven out of twelve combinations of serovar pairs and materials had attachment ratios not significantly different(P>0.05) from the initial ratio of 0.428. Five out of twelve and ten out of twelve samples had attachment ratios not significantly different (P>0.05) from the initial ratios of 1 and 2.333 respectively. These results demonstrate that bacterial attachment to different materials is likely to be non-stochastic only when the key physicochemical properties of the bacteria were significantly different (P<0.05) from each other. XDLVO theory could successfully predict the attachment of some individual isolates to particular materials but could not be used to predict the likelihood of stochasticity in pair-wise attachment experiments.