Bacterial adherence to hydrocarbons and to surfaces in the oral cavity

Adhesion of Bacillus spores and Escherichia coli cells to inert surfaces: role of surface hydrophobicity

The ability of bacterial spores and vegetative cells to adhere to inert surfaces was investigated by means of the number of adherent spores (Bacillus cereus and Bacillus subtilis spores) and Escherichia coli cells and their resistance to cleaning or rinsing procedures (adhesion strength). Six materials (glass, stainless steel, polyethylene high density (PEHD), polyamide-6, polyvinyl chloride, and Teflon) were tested. Slight differences in the number of adherent spores (less than 1 log unit) were observed between materials, but a higher number of adherent E. coli cells was found on the hydrophobic materials PEHD and Teflon. Conversely, the resistance of both B. cereus and B. subtilis spores to a cleaning procedure was significantly affected by the material. Hydrophobic materials were harder to clean. The topography parameter derived from the Abbott-Firestone curve, RVK, and, to a lesser extent, the widely used roughness parameters RA (average roughness) and Rz (maximal roughness), were related to the number of adherent cells. Lastly, the soiling level as well as the adhesion strength were shown to depend largely on the microorganism. The number of adhering B. cereus hydrophobic spores and their resistance to a cleaning procedure were found to be 10 times greater than those of the B. subtilis hydrophilic spores. Escherichia coli was loosely bound to all the materials tested, even after 24 h biofilm formation.

A rapid and selective assay for measuring cell surface hydrophobicity of brewer's yeast cells

A rapid and selective assay was developed to measure cell surface hydrophobicity of brewer's yeast cells. During this so-called magnobead assay, bottom-fermenting yeast cells adhere to paramagnetic, polystyrene-coated latex beads which can easily be removed from the cell suspension by using a (samarium-cobalt) magnet. At pH 4 center dot 5, electrostatic repulsion between yeast cells and latex beads was found to be minimal and yeast cell adhesion was predominantly based on hydrophobic interactions. The percentage of cells adhering to the beads could be calculated and provided a measure for cell surface hydrophobicity. Cell surface hydrophobicity measured by the magnobead assay was found to yield similar results, as did determination of contact angles of water droplets on a layer of yeast cells, a standard method for measuring surface hydrophobicity. However, the magnobead assay has the following advantages: (i) it is a quick and simple method, and, more significantly, (ii) hydrophobicity can be measured under physiological conditions. Use of the magnobead assay confirmed that a higher level of cell surface hydrophobicity is correlated with stronger flocculence of brewer's lager yeast cells.

Postantibiotic effect of roxithromycin on streptolysin O production, hydrophobicity, and bactericidal activity of PMNL by Streptococcus pyogenes

Exposure of Streptococcus pyogenes to 5 x minimum inhibitory concentration of roxithromycin for 1 h produced a significant postantibiotic effect. More than 2.5 h was necessary for roxithromycin-treated bacteria to increase by 1 log10 in colony-forming units after drug removal, compared with the unexposed cells. After exposure to and removal of the drug, treated cells failed to exhibit normal hemolytic activity for at least 4 h. The inhibitory effect persisted for 20 h after drug removal, although the extent of growth for treated and untreated cells was almost the same. Hydrophobicity of treated cells, studied throughout the logarithmic growth phase with a water-hexadecan two-phase system, was markedly decreased by 40%, compared with untreated cells 4 h after drug removal. Cells that had been treated with roxithromycin became more susceptible to the bactericidal activity of human PMNL than untreated bacteria. The data indicate that some of the metabolic activity that contributes to the virulence of S. pyogenes is affected by postexposure to roxithromycin, and its minimum inhibitory concentration and serum level might not be the best indicators of efficacy in this class of drugs.

Retention of streptococci to defined solid surfaces in the presence of saliva secretions

The initial surface retention of Streptococcus sanguis (G9B and ATCC 10556) and Streptococcus salivarius (ATCC 9758 and ATCC 13419) was examined using a well defined flow cell system. The microorganisms, known to be recovered from hard vs. soft tissue surfaces, respectively, were suspended in either Ringer solution, human parotid saliva (HPS), human submandibular and sublingual saliva (HSMSL), or mixed saliva. Microbial retention was evaluated on germanium prisms of low (20-25 mNm-1) and medium (30-35 mNm-1) critical surface tensions following distilled water rinse at 1 ml/min for 15 min. When suspended in only Ringer solution, the tested microorganisms showed patterns of generally high retention, that reflected the influence of both bacterial and substratum surface properties. However, in the saliva suspensions an overall reduction of retention was found with preferential retention to surfaces of medium critical surface tension for all bacteria. When comparing HPS and HSMSL as the suspending medium, a statistically significant observation was that smaller numbers of retained bacteria were recorded in the presence of HSMSL. The most frequently observed relationship between the tested salivas and numbers of retained cells was HSMSL less than MIXED less than HPS.

Effect of Cetylpyridinium Chloride on Microbial Adhesion to Hexadecane and Polystyrene

Microbial adhesion at the oil-water interface is a subject of both basic interest (e.g., as a technique for the measurement of hydrophobicity) and applied interest (e.g., for use in two-phase oil-water mouthwashes for the desorption of oral microorganisms). In general, surfactants inhibit microbial adhesion to oils and other hydrophobic surfaces. In the present study, we demonstrated that the cationic surfactant cetylpyridinium chloride (CPC) significantly enhanced microbial adhesion to hexadecane and various oils, as well as to the solid hydrophobic surface polystyrene. CPC increased adhesion to hexadecane of Escherichia coli, Candida albicans and Acinetobacter calcoaceticus MR-481 and of expectorated oral bacteria from near 0% to over 90%. The CPC concentration required for optimal enhancement of adhesion was a function of the initial cell density. This phenomenon was inhibited by high salt concentrations and, in the case of E. coli , by a low pH. CPC-pretreated cells were able to bind to hexadecane, but CPC-pretreated hexadecane was unable to bind untreated cells. Another cationic, surface-active antimicrobial agent, chlorhexidine gluconate, was similarly able to promote microbial adhesion to hexadecane. The results suggest that (i) CPC enhances microbial adhesion to hexadecane by binding via electrostatic interactions at the cell surface, thus diminishing surface charge and increasing cell surface hydrophobicity, and (ii) this phenomenon may have applications in oral formulations and in the use of hydrocarbon droplets as a support for cell immobilization.

Glucan-binding factor in saliva

High-molecular-weight polymers of alpha-1,6-linked D-glucans are insoluble in alcohol solutions. Whole, but not parotid, saliva prevented the precipitation of D-glucans by 80% (vol/vol) ethanol, showing that the whole saliva contained a factor which complexed with the glucan to render it alcohol soluble. The glucan-binding factor was retained on a column of Sephacryl S-200 which had been preequilibrated with 80% ethanol. The factor was then eluted with water. Passive hemagglutination assays revealed that the glucan-binding factor could sensitize erythrocytes to agglutination with anti-poly(glycerolphosphate), suggesting that the active glucan-binding component with lipoteichoic acid. The glucan-solubilizing factor was resistant to heat (100 degrees C), proteases, sialidase, lysozyme, lactoperoxidase, trichloroacetic acid, and Triton X-100. When sucrose was added to saliva, a suspension of Streptococcus cricetus AHT, or a suspension of Streptococcus sanguis 10556, relatively large amounts of glucan-binding factor were released in a soluble form. In addition, penicillin G caused the release of the glucan-solubilizing component from a suspension of S. cricetus AHT. It is suggested that whole saliva contains a component, tentatively identified as lipoteichoic acid, which can complex with glucans in a relatively hydrophobic solvent. This type of complex formation may be important in the adhesion of oral streptococci to saliva-coated surfaces.

The hydrophobicity of 'viridans' streptococci isolated from the human mouth

The hydrophobicity of human oral streptococci was measured with the hexadecane assay modified by the incorporation of polyethylene glycol 6000. Large variability in the hydrophobicity between cultures of some strains grown on different occasions was observed whereas other strains were less variable. The variation in hydrophobicity was significantly reduced by growing the cells in continuous culture in a chemostat under glucose-limiting conditions. The Streptococcus mutans strains used all had low hydrophobicity and the mean hydrophobicity of this species was significantly lower (P less than 0.05) than the mean hydrophobicity of Strep. salivarius, Strep. sanguis Type I and Strep. sanguis Type II strains. This finding supports the view that hydrophobicity is a contributing factor in the adhesion of viridans streptococci to oral surfaces.

Kinetic analysis of Streptococcus sanguis adhesion to artificial pellicle

Studies of equilibria between Streptococcus sanguis and artificial pellicle have suggested that there are multiple binding sites for the organism. In the present study, adhesion of S. sanguis to saliva-coated hydroxylapatite was examined by means of kinetic methods. Cell-pellicle complex formation was measured from initiation of binding to equilibrium. Rate constants were calculated for forward reactions (adsorption) and reverse reactions (desorption). Initial binding obeyed reversible, first-order kinetics, whereas desorption of bound cells followed biphasic kinetics. Initial desorption proceeded approximately ten times faster than the slower second rate. The results are consistent with the mechanism C + P reversible CP* in equilibrium with CP in which CP* represents the reversible equilibrium that shifts at a discrete rate to the high-affinity CP state. Thus, the biphasic binding behavior that has been previously deduced from equilibrium studies may be attributed to a time-dependent shift from close apposition to pellicle, stabilized by low-specificity forces, to a higher-affinity binding.

Evidence for Separate Adhesion Mechanisms for Hydrophilic and Hydrophobic Surfaces in Vibrio proteolytica

The proteolytic enzymes pronase, trypsin, and chymotrypsin and the surfactant Triton X-100 inhibited attachment of Vibrio proteolytica to the hydrophobic substratum polystyrene by >97%. These treatments had no effect on attachment to hydrophilic substrata such as glass or tissue culture dishes. Both pronase and Triton X-100 effected the removal of previously attached cells from polystyrene but not from hydrophilic surfaces. Removal of cells from polystyrene by pronase left material (which we have termed footprints) that stained with the protein-specific stain Hoechst 2495 but not with the DNA-specific stain Hoechst 33342. Pronase treatment also caused a significant decrease in cell surface hydrophobicity as determined by phase partitioning in hexane or petroleum ether. Collectively, these results imply the existence of separate mechanisms for the adhesion of V. proteolytica to hydrophilic and hydrophobic substrata and suggest a role for protein in the latter mechanism.

Adhesion of Streptococcus sanguis CH3 to polymers with different surface free energies

The adhesion of the oral bacterium Streptococcus sanguis CH3 to various polymeric surfaces with surface free energies (gamma s) ranging from 22 to 141 erg cm-2 was investigated. Suspensions containing nine different bacterial concentrations (2.5 X 10(7) to 2.5 X 10(9) cells per ml) were used. After adhesion for 1 h at 21 degrees C and a standardized rinsing procedure, the number of attached bacteria per square centimeter (nb) was determined by scanning electron microscopy. The highest number of bacteria was consistently found on polytetrafluorethylene (gamma s = 22 erg cm-2), and the lowest number was found on glass (gamma s = 141 erg cm-2) at all bacterial concentrations tested. The overall negative correlation between nb and gamma s was weak. However, the slope of the line showing this decrease, calculated from an assumed linear relationship between nb and gamma s, appeared to depend strongly on the bacterial concentration and increased with increasing numbers of bacteria in the suspension. Analysis of the data for each separate polymer showed that the numbers of attached cells on polyvinyl chloride and polypropylene were higher but that those on polycarbonate were lower than would be expected on basis of a linear relationship between nb and gamma s. Desorption experiments were performed by first allowing the bacteria to attach to substrata for 1 h, after which the substrata and attached bacteria were removed to bacterial suspensions containing 10-fold lower bacterial concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of stereochemical interactions in the adhesion of Streptococcus sanguis C5 to experimental pellicles

Parameters for the adsorption of Streptococcus sanguis C5 to experimental salivary pellicles were determined to assess the relative contributions of stereochemical and less specific hydrophobic-electrostatic interactions in this process. S. sanguis C5 cells possess hydrophobic surfaces and also an adhesin which exhibits stereochemical binding to sialic acid-containing salivary receptors. The adsorption of S. sanguis C5 to untreated pellicles was significantly better described by a two-site adsorption model than by a one-site model (p less than 0.001). One class of binding sites had an affinity for the organism that was more than 400 times that of the second class of binding sites. However, adsorption of the organism was better described by a one-site model to asialo pellicles prepared by neuraminidase treatment which destroyed the receptors for the organism's adhesin. The affinity of the organism to sites in asialo pellicles was low, and approximated that to the low-affinity sites in untreated pellicles. These observations suggest that, in the absence of stereochemical interactions involving the organism's adhesin and specific salivary receptors, S. sanguis C5 cells only exhibit low-affinity binding to experimental pellicles. This was substantiated by studies which showed that adsorption of the organism to albumin-coated hydroxyapatite and to polystyrene beads was also better described by a one-site model, and it occurred with only low affinity.

Factors affecting binding of galacto ligands to Actinomyces viscosus lectin

The specificity requirements for the binding of Actinomyces viscosus T14V were examined by testing simple sugars, oligopeptides, and glycoproteins as inhibitors of the aggregation of glycoprotein-coated latex beads and washed A. viscosus cells. Lactose was the most inhibitory simple sugar; D-fucose and D-galactose were equally inhibitory, methyl-alpha-D-fucoside was slightly less inhibitory, and L-fucose and raffinose were not inhibitory. The concentration of galactose residues required for 50% inhibition of aggregation was 15 times higher in the form of lactose than in the form of asialoglycoprotein, suggesting an enhancement of lectin binding when galactose residues are clustered. However, when the inhibitory power of bi-, tri-, and tetraantennary asialooligopeptides of alpha 1-acid glycoprotein was compared with that of equivalent concentrations of galactose in the form of lactose, the biantennary form was slightly less effective than lactose, the triantennary form was approximately as effective as lactose, and the tetraantennary form was slightly more effective than lactose. Steric interference may prevent this type of clustering from enhancing lectin binding. The O-linked asialooligopeptides of asialofetuin were 10 times more inhibitory than an equivalent concentration of galactose in the form of N-linked asialooligopeptides. Thus, galactose beta-1----3 linked to N-acetylgalactosamine exhibits greater specificity for the A. viscosus lectin than does galactose beta-1----4 linked to N-acetylglucosamine. These results, taken together with previously reported data, are consistent with a lectin of low affinity, binding enhanced by multivalency, and specificity for beta-linked galactose.