An EPR investigation of surfactant action on bacterial membranes

SURFACTANT PROMOTION OF THE INHIBITORY EFFECTS OF CUPRIC GLUTAMATE ON THE DINOFLAGELLATE ALEXANDRIUM(1)

We studied cupric glutamate as a novel algicide for marine harmful algae and hexadecyltrimethyleamine bromide (HDTMAB) as an accelerant. Cupric glutamate had an excellent ability to inhibit the growth of Alexandrium sp. LC3, but the inhibition efficiency did not increase with higher cupric glutamate concentration. The studies on the inhibition ofAlexandrium sp. LC3 by cupric sulfate or cupric glutamate showed that cupric glutamate had a higher inhibition rate than cupric sulfate (P < 0.05). HDTMAB could significantly enhance the inhibition by cupric glutamate (P < 0.05). Ultrastructural changes of Alexandrium sp. LC3 under cupric sulfate, cupric glutamate, and cupric glutamate-HDTMAB combined treatment were studied with TEM. Under these stresses, the integrity of the cell plasma membranes (cell plasma membrane, chloroplast and mitochondria membranes) was destroyed. The degree of damage under cupric glutamate-HDTMAB combined treatment was more severe than under the other stresses. These results indicated that mechanistically cupric glutamate inhibits algal growth by destroying the cell membranes, and that HDTMAB promotes this process, which induced mass extravasation of intracellular components and more copper ion entry into the plasma.

Investigation into the effect of detergents on disinfectant susceptibility of attached Escherichia coli and Listeria monocytogenes

AIMS

Investigate the effect of detergent treatment on susceptibility of attached Escherichia coli and Listeria monocytogenes to subsequent disinfectant treatment.

METHODS AND RESULTS

Plate counts show that E. coli attached to stainless steel surfaces became significantly more susceptible to benzalkonium chloride (BAC) after treatment with sodium alkyl sulfate (SAS) and fatty alcohol ethoxylate (FAE). No change in susceptibility was observed with Sodium dodecyl sulfate (SDS). L. monocytogenes became significantly less susceptible to BAC after treatment with SAS and SDS yet no change in susceptibility was observed with FAE. Flow cytometry using the fluoresceine propidium iodide revealed significant increases in cell membrane permeability of both organisms by SAS and FAE, although the effect was much greater in E. coli. No change was observed with SDS. Hydrophobic interaction chromatography showed that both organisms became less hydrophobic following treatment with SAS and SDS but FAE had no effect.

CONCLUSIONS

In E. coli, detergents that increase susceptibility to BAC increase membrane permeability. In L. monocytogenes, detergents that reduce susceptibility to BAC lower cell surface hydrophobicity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Detergents can influence the sensitivity of pathogenic food borne micro-organisms to BAC.

Use of a whole-cell biosensor to assess the bioavailability enhancement of aromatic hydrocarbon compounds by nonionic surfactants

The whole-cell bioluminescent biosensor Pseudomonas putida F1G4 (PpF1G4), which contains a chromosomally-based sep-lux transcriptional fusion, was used as a tool for direct measurement of the bioavailability of hydrophobic organic compounds (HOCs) partitioned into surfactant micelles. The increased bioluminescent response of PpF1G4 in micellar solutions (up to 10 times the critical micellar concentration) of Triton X-100 and Brij 35 indicated higher intracellular concentrations of the test compounds, toluene, naphthalene, and phenanthrene, compared to control systems with no surfactants present. In contrast, Brij 30 caused a decrease in the bioluminescent response to the test compounds in single-solute systems, without adversely affecting cell growth. The decrease in bioluminescent response in the presence of Brij 30 did not occur in the presence of multiple HOCs extracted into the surfactant solutions from crude oil and creosote. The effect of the micellar solutions on the toluene biodegradation rate was consistent with the bioluminescent response in single-solute systems. None of the surfactants were toxic to PpF1G4 at the doses employed in this study, and PpF1G4 did not produce a bioluminescent response to the surfactants nor utilize them as growth substrates. TEM images suggest that the surfactants did not rupture the cell membranes. The results demonstrate that for Pseudomonas putida F1, nonionic surfactants such as Triton X-100 and Brij 35, at doses between 2 and 10 CMC, may increase the bioavailability and direct uptake of micellar phase HOCs that are common pollutants at contaminated sites.

Antimicrobial mechanisms of ortho-phthalaldehyde action

Biocides generally have multiple biochemical targets. Such a feature easily entangles the analysis of the mechanisms of antimicrobial action. In this study, the action of the dialdehyde biocide ortho-phtalaldehyde (OPA), on bacteria, was investigated using the Gram-negative Pseudomonas fluorescens. The targets of the biocide action were studied using different bacterial physiological indices. The respiratory activity, membrane permeabilization, physico-chemical characterization of the bacterial surfaces, outer membrane proteins (OMP) expression, concomitant influence of pH, contact time and presence of bovine serum albumin (BSA) on respiratory activity, morphological changes and OPA-DNA interactions were assessed for different OPA concentrations. With the process conditions used, the minimum inhibitory concentration was 1500 mg/l, the concentration to promote total loss of bacterial culturability was 65 mg/l and the concentration needed to inactivate respiratory activity was 80 mg/l. These data are evidence that culturability and respiratory activity were markedly affected by the biocide. OPA lead, moreover, to a significant change in cell surface hydrophobicity and induced propidium iodide uptake. Such results suggest cytoplasmic membrane damage, although no release of ATP was detected. At pH 5, the bactericidal action of OPA was stronger, though not influenced by BSA presence. Nevertheless, at pH 9, BSA noticeably (p < 0.05) impaired biocide action. A time-dependent effect in OPA action was evident when contemplating respiratory activity variation, mainly for the lower exposure times. Scanning electron microscopy allowed to detect bacterial morphological changes, translated on cellular elongation, for OPA concentrations higher than 100 mg/l. Interferences at DNA level were, however, restricted to extreme biocide concentrations. The overall bactericidal events occurred without detectable OMP expression changes. In conclusion, the results indicated a sequence of events responsible for the antimicrobial action of OPA: it binds to membrane receptors due to cross-linkage; impairs the membrane functions allowing the biocide to enter through the permeabilized membrane; it interacts with intracellular reactive molecules, such as RNA, compromising the growth cycle of the cells and, at last, with DNA.

Interaction of four monoterpenes contained in essential oils with model membranes: implications for their antibacterial activity

The present article reports the antimicrobial efficacy of four monoterpenes (thymol, carvacrol, p-cymene, and gamma-terpinene) against the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Escherichia coli. For a better understanding of their mechanism of action, the damage caused by these four monoterpenes on biomembranes was evaluated by monitoring the release, following exposure to the compounds under study, of the water-soluble fluorescent marker carboxyfluorescein (CF) from large unilamellar vesicles (LUVs) with different lipidic composition (phosphatidylcholine, PC, phosphatidylcholine/phosphatidylserine, PC/PS, 9:1; phosphatidylcholine/stearylamine, PC/SA, 9:1). Furthermore, the interaction of these terpenes with dimyristoylphosphatidylcholine multilamellar vesicles as model membranes was monitored by means of differential scanning calorimetry (DSC) technique. Finally, the results were related also with the relative lipophilicity and water solubility of the compounds examined. We observed that thymol is considerably more toxic against S. aureus than the other three terpenes, while carvacrol and p-cymene are the most inhibitory against E. coli. Thymol and carvacrol, but not gamma-terpinene and p-cymene, caused a concentration-dependent CF leakage from all kinds of LUVs employed; in particular, thymol was more effective on PC and PC/SA LUVS than on PC/PS vesicles, while carvacrol challenge evoked a CF leakage from PC/PS LUVs similar to that induced from PC/SA LUVs, and lower than that measured with PC vesicles. Concerning DSC experiments, these four terpenes caused a decrease in Tm and (especially carvacrol and p-cymene) DeltaH values, very likely acting as substitutional impurities. Taken together, our findings lead us to speculate that the antimicrobial effect of thymol, carvacrol, p-cymene, and gamma-terpinene may result, partially at least, from a gross perturbation of the lipidic fraction of the plasmic membrane of the microorganism. In addition to being related to the physicochemical characteristics of the compounds (such as lipophilicity and water solubility), this effect seems to be dependent on the lipidic composition and net surface charge of the microbic membranes. Furthermore, the compounds might cross the cell membranes, thus penetrating into the interior of the cell and interacting with intracellular sites critical for antibacterial activity.

Passive diffusion of polymeric surfactants across lipid bilayers

Self-assembling polymeric surfactant, mmePEG(750)P(CL-co-TMC) [monomethylether poly(ethylene glycol)(750)-poly(caprolactone-co-trimethylene carbonate)], increases drug solubility and crosses an enterocyte monolayer both in vitro and in vivo. The aims of the present work were to investigate whether mmePEG(750)P(CL-co-TMC) polymers can diffuse passively through lipid bilayer using parallel artificial membrane permeability assay (PAMPA) and affect membrane properties using liposomes as model. The mmePEG(750)P(CL-co-TMC) polymer was able to cross by passive diffusion an enterocyte-mimicking membrane in PAMPA at concentration which did not perturb membrane integrity. A weak rigidification associated with a low increase in permeability of liposomal lipid bilayers was observed. These data suggest that polymeric surfactants can cross the lipid membrane by passive diffusion and interact with lipid bilayers.

Mechanism of inhibition of P-glycoprotein mediated efflux by vitamin E TPGS: influence on ATPase activity and membrane fluidity

Efflux pump (e.g., P-gp, MRP1, and BCRP) inhibition has been recognized as a strategy to overcome multi-drug resistance and improve drug bioavailability. Besides small-molecule inhibitors, surfactants such as Tween 80, Cremophor EL, several Pluronics, and Vitamin E TPGS (TPGS 1000) are known to modulate efflux pump activity. Competitive inhibition of substrate binding, alteration of membrane fluidity, and inhibition of efflux pump ATPase have been proposed as possible mechanisms. Focusing on TPGS 1000, the aim of our study was to unravel the inhibitory mechanism by comparing the results of inhibition experiments in a Caco-2 transport assay with data from electron spin resonance (ESR) and from ATPase activity studies. ESR results, on Caco-2 cells using 5-doxyl stearic acid (5-SA) as a spin probe, ruled out cell membrane fluidization as a major contributor; change of membrane fluidity was only observed at surfactant concentrations 100 times higher than those needed to achieve full efflux inhibition. Concurrently, TPGS 1000 inhibited substrate induced ATPase activity without inducing significant ATPase activity on its own. By investigating TPGS analogues that varied by their PEG chain length, and/or possessed a modified hydrophobic core, transport studies revealed that modulation of ATPase activity correlated with inhibitory potential for P-gp mediated efflux. Hence, these results indicate that ATPase inhibition is an essential factor in the inhibitory mechanism of TPGS 1000 on cellular efflux pumps.

Physiological aspects. Part 1 in a series of papers devoted to surfactants in microbiology and biotechnology

Surfactants, both chemical and biological, are amphiphilic compounds which can reduce surface and interfacial tensions by accumulating at the interface of immiscible fluids and increase the solubility, mobility, bioavailability and subsequent biodegradation of hydrophobic or insoluble organic compounds. Investigations on their impacts on microbial activity have generally been limited in scope to the most common and best characterized surfactants. Recently a number of new biosurfactants have been described and accelerated advances in molecular and cellular biology are expected to expand our insights into the diversity of structures and applications of biosurfactants. Biosurfactants play an essential natural role in the swarming motility of microorganisms and participate in cellular physiological processes of signaling and differentiation as well as in biofilm formation. Biosurfactants also exhibit natural physiological roles in increasing bioavailability of hydrophobic molecules and can complex with heavy metals, and some also possess antimicrobial activity. Chemical- and indeed bio-surfactants may also be added exogenously to microbial systems to influence behaviour and/or activity, mimicking the latter effects of biosurfactants. They have been exploited in this way, for example as antimicrobial agents in disease control and to improve degradation of chemical contaminants. Chemical surfactants can interact with microbial proteins and can be manipulated to modify enzyme conformation in a manner that alters enzyme activity, stability and/or specificity. Both chemical- and bio-surfactants are potentially toxic to specific microbes and may be exploited as antimicrobial agents against plant, animal and human microbial pathogens. Because of the widespread use of chemical surfactants, their potential impacts on microbial communities in the environment are receiving considerable attention.

Detergent-like actions of linear amphipathic cationic antimicrobial peptides

Antimicrobial peptides have raised much interest as pathogens become resistant against conventional antibiotics. We review biophysical studies that have been performed to better understand the interactions of linear amphipathic cationic peptides such as magainins, cecropins, dermaseptin, delta-lysin or melittin. The amphipathic character of these peptides and their interactions with membranes resemble the properties of detergent molecules and analogies between membrane-active peptide and detergents are presented. Several models have been suggested to explain the pore-forming, membrane-lytic and antibiotic activities of these peptides. Here we suggest that these might be 'special cases' within complicated phase diagrams describing the morphological plasticity of peptide/lipid supramolecular assemblies.

Comparative antibacterial potential of selected aldehyde-based biocides and surfactants against planktonic Pseudomonas fluorescens

The antimicrobial efficacy of two aldehyde-based biocides (glutaraldehyde, GTA, and ortho-phthalaldehyde, OPA) and two surfactants (cetyltrimethyl ammonium bromide, CTAB, and sodium dodecyl sulphate, SDS) was tested against planktonic Pseudomonas fluorescens. The antimicrobial effects were evaluated by respiratory activity as a measure of the oxygen uptake rate, adenosine triphosphate (ATP) release, outer membrane proteins (OMP) expression and cellular colour changes. The results were compared with the bacterial characteristics without chemical treatment. Tests in the presence of bovine serum albumin (BSA), in order to mimic a disinfection process in the real situation under dirty conditions, were performed according to the European Standard EN-1276. P. fluorescens was completely inactivated with OPA (minimum bactericidal concentration, MBC = 0.5 mM) and CTAB (MBC = 5 mM) and was resistant to GTA and SDS. Only CTAB promoted cellular disruption and consequent ATP release. The antimicrobial action of the chemicals tested was significantly reduced when BSA was introduced into the bacterial cultures, increasing markedly the MBC values. Additionally, the presence of BSA acted as a disruption protective agent when CTAB was applied and stimulated the bacterial respiratory activity when lower concentrations of SDS were tested. The OMP of the bacterial cells was affected by the application of both surfactants. OMP expression remained unaltered after biocide treatment. Bacterial colour change was noticed after treatment with biocides and surfactants. In summary, P. fluorescens was extremely resistant to GTA and SDS, with antimicrobial action being quenched markedly by the reaction with BSA.

Promotion of hexadecyltrimethyleamine bromide to the damage of Alexandrium sp. LC3 by cupric glutamate

The effect of hexadecyltrimethyleamine bromide (HDTMAB) on the removal of Alexandrium sp. LC3 under cupric glutamate stress was investigated. Toxic effect of cupric glutamate on A lexandrium sp. LC3 was significantly promoted in the presence of HDTMAB, especially at 3.0 cmc of HDTMAB. It was found that the sulfhydryl group content of the cell decreased, while the malonaldehyde content and membrane permeability increased when Alexandrium sp. LC3 was treated with HDTMAB and cupric glutamate complex, compared with cupric glutamate alone. The data suggest that HDTMAB might stimulate the damage of Alexandrium sp. LC3 by enhancing the membrane permeability.

Permeability and thermodynamics study of quaternary ammonium surfactants—phosphocholine vesicle system

Quaternary ammonium compounds (QACs) are recognized as membrane active agents widely used as biocides. The main purpose of this work was to investigate the influence of the QAC head group and acyl chain length on their permeability-perturbing power and on their affinity for lipidic membranes. Permeability perturbations were assessed by measuring the release of calcein entrapped inside vesicles. The affinity of QACs for bilayers was investigated by isothermal titration calorimetry (ITC). QACs bearing C(16) chain were found to be more efficient to decrease the membrane permeability than their C(12) analogues. On the other hand, the chemical nature of the ammonium head group has practically no influence on the permeability perturbations caused by QACs bearing C(16) chains. It was difficult to assess the partitioning of the QACs between the aqueous and lipid phases since the ITC signals could also be associated to morphological changes such as vesicle aggregation. For the systems for which reliable thermodynamic parameters could be obtained, the Gibbs energy of transfer was similar to that for the micellization. The entropy variation represented the main contribution to the Gibbs energy, indicating that the insertion of QACs inside lipidic bilayers is driven by hydrophobic interactions.

Mechanisms of antibacterial action of three monoterpenes

In the present paper, we report the antimicrobial efficacy of three monoterpenes [linalyl acetate, (+)menthol, and thymol] against the gram-positive bacterium Staphylococcus aureus and the gram-negative bacterium Escherichia coli. For a better understanding of their mechanisms of action, the capability of these three monoterpenes to damage biomembranes was evaluated by monitoring the release, following exposure to the compounds under study, of the water-soluble fluorescent marker carboxyfluorescein from unilamellar vesicles with different lipidic compositions (phosphatidylcholine, phosphatidylcholine/phosphatidylserine [9:1], phosphatidylcholine/stearylamine [9:1], and phosphatidylglycerol/cardiolipin [9:1]). Furthermore, the interaction of the terpenes tested with dimyristoylphosphatidylcholine multilamellar vesicles as model membranes was monitored by means of differential scanning calorimetry. Finally, the results were related to the relative lipophilicity and water solubility of the compounds examined. Taken together, our findings lead us to speculate that the antimicrobial effect of (+)menthol, thymol, and linalyl acetate may result, at least partially, from a perturbation of the lipid fraction of microorganism plasma membrane, resulting in alterations of membrane permeability and in leakage of intracellular materials. Besides being related to physicochemical characteristics of the drugs (such as lipophilicity and water solubility), this effect seems to be dependent on lipid composition and net surface charge of microbial membranes. Furthermore, the drugs might cross the cell membranes, penetrating into the interior of the cell and interacting with intracellular sites critical for antibacterial activity.

Effect of surfactants on stability of Acinetobacter johnsonii S35 and Oligotropha carboxidovorans S23 coaggregates

The effect of anionic (sodium dodecyl sulphate or SDS) and cationic (cetyltrimethylammonium bromide or CTAB) surfactants on the stability of binary bacterial coaggregates comprising Acinetobacter johnsonii S35 and Oligotropha carboxidovorans S23 (both sewage sludge isolates) was studied and compared with that on the complex sewage sludge flocs. Both SDS and CTAB enhanced the bacterial coaggregation at their lower concentrations of 0.2 and 0.07 mg ml(-1), respectively. However, complete deflocculation of coaggregates was observed at 1 mg ml(-1) SDS and 0.3 mg l(-1) CTAB concentrations. Further, sewage sludge flocs did not deflocculate in the presence of CTAB, although a concentration-dependent deflocculation was observed in the presence of SDS. A. johnsonii S35 and O. carboxidovorans S23 cells were separately pretreated (prior to coaggregation) with the surfactants. In spite of the partial (complete) loss of viability during SDS (CTAB) pretreatment, washed cells still retained hydrophobic character and displayed significant coaggregation (aggregation index ranging from 84% to 97% in comparison to 96% in the case of non-treated cells), demonstrating reversibility of the surfactant induced deflocculation. Further, when exposed to lower concentration of surfactants (0.2 mg ml(-1) SDS), coaggregates were more resistant (76% viability) as compared to the individual partner (S35: 52%; S23: 39% viability). Since the coaggregates are stable and provide protection from surfactants at lower concentrations (those normally expected in the sewage treatment plants), their presence as well as a sustained role in the sewage sludge bioflocculation is evident.

Effects of non-ionic surfactants N-alkyl-N,N-dimethylamine-N-oxides on the structure of a phospholipid bilayer: small-angle X-ray diffraction study

Effects of non-ionic surfactants N-alkyl-N,N-dimethylamine-N-oxides (C(n)NO, n is the number of alkyl carbons) on the structure of egg yolk phosphatidylcholine (EYPC) bilayers in the lamellar fluid phase was studied by small-angle X-ray diffraction as a function of H(2)O:EYPC and C(n)NO:EYPC molar ratios. The bilayer thickness d(L) and the lipid surface area at the bilayer-aqueous interface S(L) were calculated from the repeat period, d of the lamellar phase, based on the model that water and EYPC + CnNO molecules form separated layers and that their molecular volumes are additive. In the studied range of m=CnNO:EYPC molar ratios up to 1:1, d(L) and S(L) change linearly. The slopes Delta L = delta dL/ delta m and Delta S= delta S L / delta m are equal to -0.876 +/- 0.027 nm and 0.347 +/- 0.006 nm2 for C(6)NO, -1.025+/-0.060 nm and 0.433+/-0.025 nm(2) for C(8)NO, -0.836+/-0.046 nm and 0.405+/-0.018 nm(2) for C(10)NO, -0.604+/-0.015 nm and 0.375+/-0.007 nm(2) for C(12)NO, -0.279+/-0.031 nm and 0.318+/-0.005 nm(2) for C(14)NO, -0.0865+/-0.070 nm and 0.2963 +/-0.014 nm(2) for C(16)NO, and -0.040+/-0.022 nm and 0.297+/- 0.002 nm(2) for C(18)NO, respectively, at full bilayer hydration. The peak-peak distance in the bilayer electron density profile, which relates to the P-P distance d(PP), obtained from the first four diffraction peaks by the Fourier transform also depends linearly on m, and the slope Delta PP = delta dPP/delta m is -0.528+/-0.065 nm for C(6)NO, -0.680+/-0.018 nm for C(8)NO, -0.573+/-0.021 nm for C(10)NO, -0.369+/-0.075 nm for C(12)NO, -0.190+/-0.015 for C(14)NO, -0.088+/-0.016 nm for C(16)NO and -0.094+/-0.016 nm for C(18)NO. The effects of C(n)NO on Delta(L), Delta(S) and Delta(PP) are the results of C(n)NO insertion into EYPC bilayers and depend on the hydrophobic mismatch between C(n)NO and EYPC hydrocarbon chains and on the lateral interactions of C(n)NO and EYPC in the bilayer.

Development of bacterial resistance to several biocides and effects on antibiotic susceptibility

The aims of this study were to investigate the development of bacterial resistance to eugenol, thymol, trichlorocarbanalide (TCC), didecyldimethylammonium chloride (DDDMAC) and C10-16-alkyldimethyl, N-oxides (ADMAO) and subsequent effects on antibiotic susceptibility. An agar minimum inhibitory concentration (MIC) method was used to assess the activity of the biocides against standard bacterial strains and laboratory mutants. A range of techniques including disk diffusion and gradient plate experiments were used to attempt to develop bacterial 'resistance' or tolerance to the biocides. The mutants produced were examined for cross-resistance to the other biocides and to antibiotics via disk diffusion and gradient plate MIC methods. Outer membrane proteins of the mutants were extracted and examined using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Escherichia coli triclosan-resistant mutants were not cross-resistant to eugenol, thymol, TCC, DDDMAC and ADMAO. Mutants with elevated MICs to DDDMAC (E. coli and Pseudomonas aeruginosa), thymol (E. coli) and eugenol (E. coli) were isolated, but all remained sensitive to higher concentrations of the agents. Bacteria with elevated MICs to TCC and ADMAO were not obtained. Some low-level cross-resistance between DDDMAC, eugenol and thymol was observed with the E. coli gradient plate mutants, as well as reduced susceptibility to antibiotics, most notably chloramphenicol. The lack of cross-resistance of the triclosan mutants suggested that the mode of action of triclosan is not shared with the other biocides studied. SDS-PAGE results indicated that the DDDMAC P. aeruginosa mutant had a reduced amount (or absence) of one outer membrane protein in comparison with the standard strain. In conclusion, under laboratory conditions, bacterial exposure to thymol, eugenol and DDDMAC can lead to reduced susceptibility between selected biocidal agents and antibiotics, more specifically, chloramphenicol. However, further studies are required to determine if this is of clinical significance.

Spectroscopic techniques in the study of membrane solubilization, reconstitution and permeabilization by detergents

This review focuses on the use of spectroscopic techniques for the study of membrane solubilization, reconstitution, and permeabilization by detergents. Turbidity and light scattering, visible and infrared spectroscopic methods, fluorescence, nuclear magnetic resonance, electron spin resonance and X-ray diffraction are examined from the point of view of their applicability to the above detergent-mediated phenomena. A short introduction is provided about each of the techniques, and references are given for further study.