Surface Characteristics and Adhesion Behavior of Escherichia coli O157:H7: Role of Extracellular Macromolecules

Abstract

Experiments were conducted using enterohemorrhagic Escherichia coli O157:H7 cells to investigate the influence of extracellular macromolecules on cell surface properties and adhesion behavior to quartz sand. Partial removal of the extracellular macromolecules on cells by a proteolytic enzyme (proteinase K) was confirmed using Fourier transform infrared spectroscopy analyses. The proteinase K treated cells exhibited more negative electrophoretic mobility (EPM) at an ionic strength (IS) e 1 mM, a slightly lower isoelectric point, and were less hydrophobic as compared to the untreated cells. Potentiometric titration results indicated that the total site concentration (i.e., the total amount of exposed functional groups per cell) on the treated cells was approximately 22% smaller than the untreated cells, while the dissociation constants were almost identical. Analysis of the EPM data using soft particle theory showed that the removal of extracellular macromolecules resulted in polymeric layers outside the cell surface that were less electrophoretically soft. The more negative mobility for the treated cells was likely due to the combined effects of a change in the distribution of functional groups and an increase in the charges per unit volume after enzyme treatment and not just removal of extracellular macromolecules. The proteolytic digestion of extracellular macromolecules led to a significant difference in the cell adhesion to quartz sand. The adhesion behavior for treated cells was consistent with DLVO theory and increased with IS due to less negativity in the EPM. In contrast, the adhesion behavior of untreated cells was much more complex and exhibited a maximum at IS ) 1 mM. The treated cells exhibited less adhesion than the untreated cells when the IS e 1 mM due to their more negative EPM. However, when the IS g 10 mM, a sudden decrease in the removal efficiency was observed only for the untreated cells even through EPM values were similar for both treated and untreated cells. This result suggested that an additional non-DLVO type interaction, electrosteric repulsion, occurred at higher IS (g10 mM in this study) for the untreated cells due to the presence of extracellular macromolecules that hindered cell adhesion to the quartz surface. This finding provides important insight into the role of macromolecule-induced E. coli O157:H7 interactions in aquatic environments.

Contrasting effects of extracellular polymeric substances on the surface characteristics of bacterial pathogens and cell attachment to soil particles

“…No significant differences were found between the total site concentrations on full EPS-cell and on partial EPS-cell surfaces (P N 0.05). The two strains used in this study had more surface site concentrations than another pathogenic E. coli O157:H7 (2.74 × 10 −16 mol cell ) reported by Kim et al (2009b). For each surface site, the decreasing trend for site concentrations was not always observed for the four site types after EPS removal (Table 1).…”

“…Hence, the different site concentrations of cell walls for the four bacteria could explain the observed variability in the zeta potentials. At the tested pH range (5.6-5.8), the deprotonation of phosphodiester (pK a b 4.0) and carboxylic moieties (pK a b 5.6) primarily contributed to the overall net negative charges of the cells (Kim et al, 2009b). Titration results in Table 1 indicated that the sum of phosphodiester and carboxylic site ) on E. coli after CER treatment may explain the reduced amounts of surface negative charges.…”

“…E. coli EPS had higher sugar content (11.73 μg/10 8 cells) than protein (4.80 μg/10 8 cells). Thus, the major parts of the molecular composition removed by CER were likely to be the uncharged hydrocarbon compounds C\ \(C,H) in polysaccharides, which contained a relatively larger number of nonpolar sites than proteins (Kim et al, 2009b). It has been reported that the C\ \(C,H) constituents could contribute to the increase in hydrophobicity (Hamadi et al, 2008).…”

“…A number of physical and chemical factors have been proposed to govern bacteria-solid surface interactions (Stevik et al, 2004), including particle size (Soupir et al, 2010), surface coating (Li and Logan,type (Foppen et al, 2010), extracellular polymeric substances (EPSs) (Kim et al, 2009b), and lipopolysaccharides have also been shown to have considerable influence on bacterial attachment. Among the various components of bacterial cell surfaces, EPS is the major heterogeneous component composed dominantly of polysaccharides and proteins, with nucleic acids and lipids as minor constituents (Eboigbodin and Biggs, 2008;Long et al, 2009;Cao et al, 2011).…”

“…Several studies have investigated the attachment of cells with and without EPS coating to wellcharacterized minerals under controlled conditions via batch attachment tests, parallel plate flow chamber, radial stagnation point flow (RSPF) system, and packed-bed columns. For instance, by comparing the attachment efficiencies of untreated and proteinase K treated Escherichia coli O157:H7 on quartz sand in a batch system, Kim et al (2009b) reported greater cell attachment occurred for cells with EPSpartially removed when IS ≥ 10 mM, suggesting the presence of EPS hindered cell attachment. Hong et al (2013) found that via the treatment of cation exchange resin (CER), the reduction in EPS had no apparent effects on Bacillus subtilis adhesion on montmorillonite, kaolinite and goethite when the wet bacteria/mineral mass ratio was less than 0.4.…”