Hydrophobic and Electrostatic Cell Surface Properties of Thermophilic Dairy Streptococci

Abstract

Microbial adhesion to hydrocarbons (MATH) and microelectrophoresis were done in 10 mM potassium phosphate solutions to characterize the surfaces of thermophilic dairy streptococci, isolated from pasteurizers. Regardless of whether they were grown (in M17 broth) with lactose, sucrose, or glucose added, strains were relatively hydrophilic (showing low initial removal rates by hexadecane) and slightly negatively charged. A tendency exists for cells grown with sucrose added to be more hydrophilic than cells grown with glucose or lactose added. Also, the lowest isoelectric points, i.e., the pH values for which the zeta potentials are zero, were measured for strains with glucose added to the growth medium. The isoelectric points for the strains were all rather high, between pH 3 and 5, indicative of protein-rich surfaces, although X-ray photoelectron spectroscopy did not measure excessively large amounts of nitrogen on the cell surfaces. Both MATH and microelectrophoresis were done as a function of pH. Maxima in hydrophobicity were observed at certain pH values. Usually these pH values were in the range of the isoelectric points of the cells. Thus it appears that MATH measures an interplay of hydrophobicity and electrostatic interactions. MATH measures solely hydrophobicity only when electrostatic interactions are absent, i.e., close to the isoelectric points of the cells. Considering that these thermophilic streptococci are all rather hydrophilic, a possible pathway to prevent fouling in the pasteurization process might be to render the heat exchanger plates of the pasteurizer more hydrophobic.A. H.

Membrane disruption and anti-quorum sensing effects of synergistic interaction between Lavandula angustifolia (lavender oil) in combination with antibiotic against plasmid-conferred multi-drug-resistant Escherichia coli

“…Presence of hydrocarbons such as terpenes and aromatics in the EOs plays an important role in membrane toxicity as documented in the previous study (Sikkema et al 1995). The zeta potential is related to the membrane potential and reflects the metabolic state of the bacteria whereby the values became more negative at higher rates of growth (Van Der Mei et al 1993;Tymczyszyn et al 2007). This method may be exploited to further reveal the membrane effects of LV.…”

Physico-chemistry of initial microbial adhesive interactions – its mechanisms and methods for study

“…Fig. 18 presents the electrostatic interaction energy at closest approach (see Table 2) between hexadecane droplets and some thermophilic dairy streptococci as a function of their initial removal rates in the kinetic MATH assay [94]. Clearly from Fig.…”

“…18. The electrostatic interaction energy G EL (d 0 ) between hexadecane droplets and thermophilic dairy streptococci versus the microbial removal rate R 0 by hexadecane in a 10 mM potassium phosphate solution as in MATH (adapted from [94]) calculated for the minimal separation distance d 0 of 1.57 A î . say repulsions of less than 100 kT.…”

Characterization of Ccw7p cell wall proteins and the encoding genes ofSaccharomyces cerevisiaewine yeast strains: relevance for flor formation

“…Determination of cell surface hydrophobicity using the MATH test was performed as described by van der Mei et al (1993), with slight modifications. This test is based on the measurement of the distribution of cells in a two-phase (aqueous and organic) solvent system.…”

“…Hydrophobic or hydrophilic characterization of four sedimenting and six film-forming yeast strains was performed by the application of the MATH test (van der Mei et al, 1993). The results shown in Fig.…”