Self-assembly in escin-nonionic surfactant mixtures: From micelles to vesicles.

HYPOTHESIS: Saponins are a class of plant derived surfactants which are widely used in food related foams and emulsions, aerated drinks, and in pharmaceuticals and cosmetics. As a potential biosourced and renewable ingredient in a wider range of surfactant based formulations their potential is intimately associated with their mixing with synthetic surfactants. As such the nature of the mixed saponin-surfactant self-assembly is an important characteristic to investigate and understand. The unconventional structure of the saponins compared to the conventional synthetic surfactants poses some interesting constraints on the structures of the mixed aggregates. EXPERIMENTS: Small angle neutron scattering, SANS, is used to investigate the structure of the saponin, escin, mixed with a range of nonionic surfactants with different ethylene oxide groups, from triethylene glycol monododecyl ether, C12E3, to dodecaethylene glycol monododecyl ether, C12E12. FINDINGS: The scattering data reveal a complex evolution in the solution self-assembled structure with varying escin / nonionic composition and ethylene oxide chain length. The rich structural development comprises of the evolution from the elongated micelle structure of escin to the micelle structure of the nonionic surfactant. At the intermediate solution compositions the structure is predominantly planar, comprising mostly of planar / micellar mixed phases. The nature of the planar structures depend upon the ethylene oxide chain length and the solution composition, and include lamellar, bilamellar vesicle, multilamellar vesicle, and nanovesicle structures, in common with what is observed in other surfactant mixtures.

Adsorption and self-assembly properties of the plant based biosurfactant, Glycyrrhizic acid.

There is an increased interest in the use of natural surfactant as replacements for synthetic surfactants due to their biosustainable and biocompatible properties. A category of natural surfactants which are attracting much current interest is the triterpenoid saponins; surface active components found extensively in a wide range of plant species. A wide range of different saponin structures exist, depending upon the plant species they are extracted from; but regardless of the variation in structural details they are all highly surface active glycosides. Greater exploitation and application requires a characterisation and understanding of their basic adsorption and self-assembly properties. HYPOTHESIS: Glycyrrhizic acid, extracted from Licorice root, is a monodesmosidic triterpenoid saponin. It is widely used in cosmetic and pharmaceutical applications due to its anti-inflammatory properties, and is an ingredient in foods as a sweetener additive. It has an additional attraction due to its gel forming properties at relatively low concentrations. Although it has attracted much recent attention, many of its basic surface active characteristics, adsorption and self-assembly, remain relatively unexplored. How the structure of the Glycyrrhizic acid saponin affects its surface active properties and the impact of gelation on these properties are important considerations, and to investigate these are the focus of the study. EXPERIMENTS: In this paper the adsorption properties at the air-water interface and the self-assembly in solution have been investigated using by neutron reflectivity and small angle neutron scattering; in non-gelling and gelling conditions. FINDINGS: The adsorption isotherm is determined in water and in the presence of gelling additives, and compared with the adsorption behaviour of other saponins. Gelation has minimal impact on the adsorption; apart from producing a rougher surface with a surface texture on a macroscopic length scale. Globular micelles are formed in aqueous solution with modest anisotropy, and are compared with the structure of other saponin micelles. The addition of gelling agents results in only minimal micelle growth, and the solutions remain isotropic under applied shear flow.

Mixing Natural and Synthetic Surfactants: Co-Adsorption of Triterpenoid Saponins and Sodium Dodecyl Sulfate at the Air-Water Interface.

Saponins are highly surface active glycosides, derived from a wide range of plant species. Their ability to produce stable foams and emulsions has stimulated their applications in beverages, foods, and cosmetics. To explore a wider range of potential applications, their surface mixing properties with conventional surfactants have been investigated. The competitive adsorption of the triterpenoid saponin escin with an anionic surfactant sodium dodecyl sulfate, SDS, at the air-water interface has been studied by neutron reflectivity, NR, and surface tension. The NR measurements, at concentrations above the mixed critical micelle concentration, demonstrate the impact of the relative surface activities of the two components. The surface mixing is highly nonideal and can be described quantitatively by the pseudophase approximation with the inclusion of the quadratic and cubic terms in the excess free energy of mixing. Hence, the surface mixing is highly asymmetrical and reflects both the electrostatic and steric contributions to the intermolecular interactions. The relative importance of the steric contribution is reinforced by the observation that the micelle mixing is even more nonideal than the surface mixing. The mixing properties result in the surface adsorption being largely dominated by the SDS over the composition and concentration range explored. The results and their interpretation provide an important insight into the wider potential for mixing saponins with more conventional surfactants.

Surfactant/biosurfactant mixing: Adsorption of saponin/nonionic surfactant mixtures at the air-water interface.

Saponins are naturally occurring biosurfactants present in a wide range of plant species. They are highly surface active glycosides, and are used to stabilise foams and emulsions in foods, beverages and cosmetics. They have great potential for an even wider range of applications, especially when mixed with different synthetic surfactants. Understanding those mixing properties are key to the exploitation of saponins in that wider range of potential applications. The surface adsorption properties of the saponin, escin, with two conventional nonionic surfactants, polyethylene glycol surfactants, have been studied at the air-water interface using neutron reflectivity, NR, and surface tension, ST. Although the saponin and polyethylene glycol, CnEOm, surfactants are both nonionic the disparity in the relative surface activities and packing constraints result in non-ideal mixing. Comparison with the predictions of the pseudo phase approximation requires the inclusion of the quadratic, cubic and quartic terms in the expansion of the excess free energy of mixing to explain the variations in the surface composition. For escin/pentaethylene glycol monododecyl ether, C12EO5, the interaction is attractive and close to ideal. For escin/octaethylene glycol monododecyl ether, C12EO8, it is repulsive and close to the criteria for demixing. The differences in mixing behaviour are attributed to greater packing constraints imposed by the larger ethylene oxide headgroup of the C12EO8 compared to C12EO5.

Agents and spectres: Life-space on a medium secure forensic psychiatric unit.

Medium secure forensic psychiatric units are unique environments within the broader 'post asylum' landscape of mental health services. Length of stay is much greater, a recovery-focused care system is much more difficult to implement, and there is a paucity of suitable "step-down" services. The aim of this study was to examine how forensic psychiatric environments contribute to the shaping of recovery, by examining key features such as social interactions and agency. Here, we report on the findings from patients participating in a qualitative-visual study. This analysis forms part of larger study on staff and patient experiences of secure hospital space. In this paper, the analytical focus is directed towards two key elements of recovery - agency and relationality, using the concept of 'topology' and 'life-space', developed by the social psychologist Kurt Lewin. First, we explore how patients have relative freedom to move within institutional spaces, yet lack relational space. Secondly, we explore how life-space is expanded or compressed by the manner in which the patient's present life in hospital is connected or disconnected from their past or pending future. Finally, we discuss the implications of these findings for a recovery model within secure forensic settings, focused on personalisation and expanded life-space.

The performance of surfactant mixtures at low temperatures.

Optimising detergency at lower temperatures is of increasing interest due to environmental and economic factors, and requires a greater understanding of the effects of temperature on the adsorption of surfactant mixtures at interfaces. The adsorption properties of surfactant mixtures and biosurfactant/surfactant mixtures have been studied at room temperatures and at temperatures below ambient using surface tension and neutron reflectivity measurements. For the ternary surfactant mixture of octaethylene monododecyl ether, C12E8, sodium dodecyl 6-benzene sulfonate, LAS, and sodium dioxyethylene glycol monododecyl sulfate, SLES, the surface tension at the air-water interface increases with decreasing temperature. In contrast, there is a notable reduction in the increase in the surface tension with a decrease in temperature from 25 °C to 10 °C for the 5 component rhamnolipid/surfactant mixture of the mono-rhamnose, R1, and di-rhamnose, R2, with C12E8/LAS/SLES. The associated neutron reflectivity data for the ternary C12E8/LAS/SLES mixture and the significant observation is that the 3, 4, and 5-component mixtures containing rhamnolipids in conjunction with the other surfactants show changes in composition and adsorbed amounts of the individual components which are close to the experimental error. However the significant observation is that the neutron reflectivity data indicate that the improved surface tension tolerance at lower temperatures is associated with the dominance of the rhamnolipid adsorption in such mixtures. Hence the introduction of the rhamnolipids provides a tolerance to the adverse effects associated with reduced temperatures, and a potential for improved detergency at relatively low temperatures.

Saponin Adsorption at the Air-Water Interface-Neutron Reflectivity and Surface Tension Study.

Saponins are a large group of glycosides present in many plant species. They exhibit high surface activity, which arises from a hydrophobic scaffold of triterpenoid or steroid groups and attached hydrophilic saccharide chains. The diversity of molecular structures, present in various plants, gives rise to a rich variety of physicochemical properties and biological activity and results in a wide range of applications in foods, cosmetics, medicine, and several other industrial sectors. Saponin surface activity is a key property in such applications and here the adsorption of three triterpenoid saponins, escin, tea saponins, and Quillaja saponin, is studied at the air-water interface by neutron reflectivity and surface tension. All these saponins form adsorption layers with very high surface visco-elasticity. The structure of the adsorbed layers has been determined from the neutron reflectivity data and is related to the molecular structure of the saponins. The results indicate that the structure of the saturated adsorption layers is governed by densely packed hydrophilic saccharide groups. The tight molecular packing and the strong hydrogen bonds between the neighboring saccharide groups are the main reasons for the unusual rheological properties of the saponin adsorption layers.

Translational studies on a ready-to-use intramuscular injection of penethamate for bovine mastitis.

Bovine mastitis caused by bacterial infections of the mammary gland (udder) of dairy cows is a costly pathology for the dairy industry due to direct and indirect losses in production. Penethamate, a pro-drug of benzylpenicillin, is used by intramuscular injection (IM). The existing products are powders which must be reconstituted in water-for-injection and this presents difficulties in the field. Penethamate is too unstable to be formulated as an aqueous formulation but a chemically stable suspension formulation was possible in certain oils; however, some literature suggests that such formulations would have unacceptable prolonged release. The translational research proceeded iteratively from lab to the target species, rather than via laboratory animal trials. Pilot studies in cows suggested that some oily suspensions would give concentrations of benzylpenicillin, (in both blood and milk) comparable with those of the reconstituted product. A physicochemical screen and a low level in vitro-in vivo correlation (IVIVC) was cautiously used to guide selection of formulations for subsequent animal trials which have resulted in a lead formulation for good laboratory practices (GLP), good clinical practices (GCP) studies.

Self-assembly in dilute mixtures of non-ionic and anionic surfactants and rhamnolipd biosurfactants.

The self-assembly of dilute aqueous solutions of a ternary surfactant mixture and rhamnolipid biosurfactant/surfactant mixtures has been studied by small angle neutron scattering. In the ternary surfactant mixture of octaethylene glycol monododecyl ether, C12E8, sodium dodecyl 6-benzene sulfonate, LAS, and sodium dioxyethylene monododecyl sulfate, SLES, small globular interacting micelles are observed over the entire composition and concentration range studied. The modelling of the scattering data strongly supports the assumption that the micelle compositions are close to the solution compositions. In the 5-component rhamnolipid/surfactant mixture of the mono-rhamnose, R1, di-rhamnose, R2, rhamnolipids with C12E8/LAS/SLES, globular micelles are observed over much of the concentration and composition range studied. However, for solutions relatively rich in rhamnolipid and LAS, lamellar/micellar coexistence is observed. The transition from globular to more planar structures arises from a synergistic packing in the 5 component mixture. It is not observed in the individual components nor in the ternary C12E8/LAS/SLES mixture at these relatively low concentrations. The results provide an insight into how synergistic packing effects can occur in the solution self-assembly of complex multi-component surfactant mixtures, and give rise to an unexpected evolution in the phase behaviour.

Adsorption of hydrophobin/ß-casein mixtures at the solid-liquid interface.

The adsorption behaviour of mixtures of the proteins ß-casein and hydrophobin at the hydrophilic solid-liquid surface have been studied by neutron reflectivity. The results of measurements from sequential adsorption and co-adsorption from solution are contrasted. The adsorption properties of protein mixtures are important for a wide range of applications. Because of competing factors the adsorption behaviour of protein mixtures at interfaces is often difficult to predict. This is particularly true for mixtures containing hydrophobin as hydrophobin possesses some unusual surface properties. At ß-casein concentrations ⩾0.1wt% ß-casein largely displaces a pre-adsorbed layer of hydrophobin at the interface, similar to that observed in hydrophobin-surfactant mixtures. In the composition and concentration range studied here for the co-adsorption of ß-casein-hydrophobin mixtures the adsorption is dominated by the ß-casein adsorption. The results provide an important insight into how the competitive adsorption in protein mixtures of hydrophobin and ß-casein can impact upon the modification of solid surface properties and the potential for a wide range of colloid stabilisation applications.

Nature of the Intermicellar Interactions in Ethoxylated Polysorbate Surfactants with High Degrees of Ethoxylation.

Ethoxylated polysorbate Tween nonionic surfactants are extensively used as foam and emulsion stabilizers and in aqueous solution form globular micelles. The ethoxylated polysorbate surfactants with higher degrees of ethoxylation than the Tween surfactants exhibit some interesting self-assembly properties. Small-angle neutron scattering, SANS, measurements have revealed intermicellar interactions which are more pronounced than the hard-sphere excluded volume interactions normally associated with nonionic surfactant micelles. The interactions are interpreted as arising from the partial charge on the ether oxygen of the ethylene oxide groups. This gives rise to an effective net negative charge on the micelles, which has been determined from the SANS data and zeta potential measurements. For degrees of ethoxylation of ⩽20, the effect is relatively small. The interaction increases with increasing ethoxylation such that for a degree of ethoxylation of 50 the interaction is comparable to that of ionic surfactant micelles. Unlike the intermicellar interaction in ionic surfactant micellar solutions, which results from the charge on the micelle arising from the partial binding of counterions, the interaction between ethoxthylated polysorbate surfactant micelles is unaffected by the addition of electrolyte.

Tuning Polyelectrolyte-Surfactant Interactions: Modification of Poly(ethylenimine) with Propylene Oxide and Blocks of Ethylene Oxide.

Significantly enhanced adsorption at the air-water interface arises in polyelectrolyte/ionic surfactant mixtures, such as poly(ethylenimine)/sodium dodecyl sulfate (PEI/SDS), down to relatively low surfactant concentrations due to a strong surface interaction between the polyelectrolyte and surfactant. In the region of charge neutralization this can result in precipitation or coacervation and give rise to undesirable properties in many applications. Ethoxylation of the PEI can avoid precipitation, but can also considerably weaken the interaction. Localization of the ethoxylation can overcome these shortcomings. Further manipulation of the polyelectrolyte-surfactant interaction can be achieved by selective ethoxylation and propoxylation of the PEI amine groups. Neutron reflectivity and surface tension data are presented here which show how the polyelectrolyte-surfactant interaction can be manipulated by tuning the PEI structure. Using deuterium labeled surfactant and polymer the neutron reflectivity measurements provide details of the surface composition and structure of the adsorbed layer. The general pattern of behavior is that at low surfactant concentrations there is enhanced surfactant adsorption due to the strong surface interaction; whereas around the region of the SDS critical micellar concentration, cmc, the surface is partially depleted of surfactant in favor bulk aggregate structures. The results presented here show how these characteristic features of the adsorption are affected by the degree of ethoxylation and propoxylation. Increasing the degree of propoxylation enhances the surfactant adsorption, whereas varying the degree of ethoxylation has a less pronounced effect. In the region of surfactant surface depletion increasing both the degree of ethoxylation and propoxylation result in an increased surface depletion.

Susceptibility to antimicrobials of mastitis-causing Staphylococcus aureus, Streptococcus uberis and Str. dysgalactiae from New Zealand and the USA as assessed by the disk diffusion test.

OBJECTIVE: To compare the antimicrobial susceptibility patterns of three common mastitis pathogens (Staphylococcus aureus, Streptococcus uberis and Str. dysgalactiae) isolated from milk samples from New Zealand and the USA. METHODS: A total of 182 S. aureus, 126 Str. uberis and 89 Str. dysgalactiae isolates from New Zealand (107, 106 and 41, respectively) and the USA (75, 20 and 48, respectively) were assessed using the disk diffusion test. RESULTS: Susceptibility varied among the bacterial species. All isolates were susceptible to the amoxicillin-clavulanic acid combination. Resistance to lincomycin was most frequent (susceptibility of 8.6%) across all species. Non-susceptible (i.e. resistant or intermediate) isolates of S. aureus were identified for the three non-isoxazolyl penicillins (amoxicillin, ampicillin and penicillin: 20.6% and 36.0%) and lincomycin (99.9% and 94.6%) for NZ and the USA, respectively. Resistance to erythromycin (5.3%) and tetracyclines (6.7%) was detected only in isolates from the USA. There were differences in susceptibility between Str. uberis and Str. dysgalactiae; all streptococcal isolates demonstrated resistance to aminoglycosides (neomycin 52.4% and streptomycin 27.9%) and enrofloxacin (28%). Resistance of Str. dysgalactiae to tetracycline was almost 100.0% and to oxytetracycline 89.9%. CONCLUSION AND CLINICAL RELEVANCE: Most of the isolates tested were susceptible to most of the antimicrobials commonly used for treatment of bovine mastitis, with the exception of the lincosamides. Susceptibility to a selected class-representative antimicrobial and at the genus level should be interpreted with caution. Differences between NZ and the USA confirm the value of national surveys to determine the susceptibility patterns of mastitis pathogens.

Adsorption of Bovine Serum Albumin (BSA) at the Oil/Water Interface: A Neutron Reflection Study.

The structure of the adsorbed protein layer at the oil/water interface is essential to the understanding of the role of proteins in emulsion stabilization, and it is important to glean the mechanistic events of protein adsorption at such buried interfaces. This article reports on a novel experimental methodology for probing protein adsorption at the buried oil/water interface. Neutron reflectivity was used with a carefully selected set of isotopic contrasts to study the adsorption of bovine serum albumin (BSA) at the hexadecane/water interface, and the results were compared to those for the air/water interface. The adsorption isotherm was determined at the isoelectric point, and the results showed that a higher degree of adsorption could be achieved at the more hydrophobic interface. The adsorbed BSA molecules formed a monolayer on the aqueous side of the interface. The molecules in this layer were partially denatured by the presence of oil, and once released from the spatial constraint by the globular framework they were free to establish more favorable interactions with the hydrophobic medium. Thus, a loose layer extending toward the oil phase was clearly observed, resulting in an overall broader interface. By analogy to the air/water interface, as the concentration of BSA increased to 1.0 mg mL(-1) a secondary layer extending toward the aqueous phase was observed, possibly resulting from the steric repulsion upon the saturation of the primary monolayer. Results clearly indicate a more compact arrangement of molecules at the oil/water interface: this must be caused by the loss of the globular structure as a consequence of the denaturing action of the hexadecane.

An approach for identifiability of population pharmacokinetic-pharmacodynamic models.

Mathematical models are routinely used in clinical pharmacology to study the pharmacokinetic and pharmacodynamic properties of a drug in the body. Identifiability of these models is an important requirement for the success of these clinical studies. Identifiability is classified into two types, structural identifiability related to the structure of the mathematical model and deterministic identifiability which is related to the study design. There are existing approaches for assessment of structural identifiability of fixed-effects models, although their use appears uncommon in the literature. In this study, we develop an informal unified approach for simultaneous assessment of structural and deterministic identifiability for fixed and mixed-effects pharmacokinetic or pharmacokinetic-pharmacodynamic models. This approach uses an information theoretic framework. The method is applied both to simple examples to explore known identifiability properties and to a more complex example to illustrate its utility.CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e49; doi:10.1038/psp.2013.25; advance online publication 19 June 2013.

Investigating the origins of nanostructural variations in differential ethnic hair types using X-ray scattering techniques.

OBJECTIVE: Human hair is a major determinant of visual ethnic differentiation. Although hair types are celebrated as part of our ethnic diversity, the approach to hair care has made the assumption that hair types are structurally and chemically similar. Although this is clearly not the case at the macroscopic level, the intervention of many hair treatments is at the nanoscopic and molecular levels. The purpose of the work presented here is to identify the main nanoscopic and molecular hierarchical differences across five different ethnic hair types from hair fibres taken exclusively from the scalp. These are Afro (subdivided into elastic 'rubber' and softer non-elastic 'soft'), Chinese, European and Mullato (mixed race). METHODS: Small angle X-Ray scattering (SAXS) is a technique capable of resolving nanostructural variations in complex materials. Individual hair fibres from different ethnic hair types were used to investigate structural features found in common and also specific to each type. Simultaneous wide angle X-Ray scattering (WAXS) was used to analyse the submolecular level structure of the fibrous keratin present. The data sets from both techniques were analysed with principal component analysis (PCA) to identify underlying variables. RESULTS: Principal component analysis of both SAXS and WAXS data was shown to discriminate the scattering signal between different hair types. The X-ray scattering results show a common underlying keratin intermediate filament (KIF) structure. However, distinct differences were observed in the preferential orientation and intensity signal from the lipid component of the hair. In addition, differences were observed in the intensity distribution of the very low-angle sample-dependent diffuse scatter surrounding the 'beamstop.' CONCLUSION: The results indicate that the fibrous keratin scaffold remains consistent between ethnic hair types. The hierarchies made by these may be modulated by variation in the content of keratin-associated proteins (KAPs) and lipids that alter the interfacial structures and lead to macroscopic differences in hair morphology.

Kinetics of surfactant desorption at an air-solution interface.

The kinetics of re-equilibration of the anionic surfactant sodium dodecylbenzene sulfonate at the air-solution interface have been studied using neutron reflectivity. The experimental arrangement incorporates a novel flow cell in which the subphase can be exchanged (diluted) using a laminar flow while the surface region remains unaltered. The rate of the re-equilibration is relatively slow and occurs over many tens of minutes, which is comparable with the dilution time scale of approximately 10-30 min. A detailed mathematical model, in which the rate of the desorption is determined by transport through a near-surface diffusion layer into a diluted bulk solution below, is developed and provides a good description of the time-dependent adsorption data. A key parameter of the model is the ratio of the depth of the diffusion layer, H(c), to the depth of the fluid, H(f), and we find that this is related to the reduced Péclet number, Pe*, for the system, via H(c)/H(f) = C/Pe*(1/2). Although from a highly idealized experimental arrangement, the results provide an important insight into the "rinse mechanism", which is applicable to a wide variety of domestic and industrial circumstances.

Culture results from milk samples submitted to veterinary diagnostic laboratories from August 2003 to December 2006 in New Zealand.

AIMS: To determine the pattern of isolation of major mastitis-causing organisms isolated from milk samples submitted to five veterinary diagnostic laboratories in New Zealand. METHODS: The culture results of 25,288 milk samples that were collected from dairy cows throughout New Zealand from August 2003 to December 2006 and submitted to a group of veterinary diagnostic laboratories were assembled, reviewed and summarised. Logistic regression was used to analyse the effect of year, region (i.e. North vs South Island), and season on the probability of isolating the two most common organisms. RESULTS: The most commonly isolated mastitis causing organisms from all samples were: Streptococcus uberis (23.6%), Staphylococcus aureus (23.5%), coagulase-negative staphylococci (CNS; 7.2%), Strep. dysgalactiae (6.2%), Bacillus spp. (4.0%), and coliforms (3.7%). The percentage of samples with isolates of Strep. uberis or Staph. aureus was affected by island, year and season (p<0.001). For most of the year, except in late winter and early spring when Strep. uberis was much more common, the percentage of isolates of Strep. uberis and Staph. aureus were not apparently different despite the former being an environmental pathogen and the other a contagious one. CONCLUSION: The pattern of isolation of major mastitis-causing organisms, as determined from culture of milk samples submitted to diagnostic laboratories in New Zealand, has changed significantly over the last 40 years, with a substantial increase in the percentage of isolates that are Strep. uberis and a decrease in isolates of Strep. agalactiae. There is a clear seasonal pattern to the isolation of both Strep. uberis and Staph. aureus, particularly the former. CLINICAL RELEVANCE: Knowledge of the aetiological agents causing bovine mastitis on a farm is of value in determining the choice of treatment. This dataset shows that, although there is seasonal pattern to the isolation of mastitis-causing organisms in New Zealand, both Strep. uberis and Staph. aureus are isolated throughout the year, so bacteriology is of value in determining aetiology even in late winter/early spring.

Efficacy of a novel internal dry period teat sealant containing 0.5% chlorhexidine against experimental challenge with Streptococcus uberis in dairy cattle.

The incidence of clinical mastitis and infection status at calving was assessed in quarters treated with 1 of 2 internal teat sealants at the time of dry off. Two contralateral quarters per cow (n=63 cows) were treated with a sealant that contained 0.5% chlorhexidine; the other quarters were treated with a commercial teat sealant. Ten cows were untreated (controls). On d 2, 4, and 16 after dry off, cows were challenged with Streptococcus uberis S210 strain. Cows were examined daily for 34 d after drying off and cases of clinical mastitis were recorded. Milk samples were collected for culture from any quarters that developed clinical mastitis during the first 34 d after drying-off and from all quarters on d -5 and 0 relative to treatment and at the first and twentieth milking after calving. The incidence of clinical mastitis during the examination period was lower in treated quarters (n=7/252; 1.5%; lower incidence for those treated with chlorhexidine-containing teat sealant n=3/126; 1.2%) than in untreated quarters (n=13/40; 26.8%). The protection against intramammary infection after calving, adjusted for the effect of cow, was higher in quarters treated with the novel teat sealant (89/105; 15.2%; 95% CI=9.6-23.4) than in those treated with the commercial teat sealant (71/104; 31.7%; 95% CI=23.5-41.3) and untreated controls (6/28; 78.6%; 95% CI=59.8-90.0), respectively. Quarters treated with teat sealants were less likely to have an intramammary infection after calving and had a lower incidence of clinical mastitis during the early dry period than did untreated controls in this challenge study.

The adsorption and self-assembly of mixtures of alkylbenzene sulfonate isomers and the role of divalent electrolyte.

In this paper, the role of the different structural isomers of the anionic surfactant sodium para-dodecyl benzene sulfonate, LAS, on surface adsorption and solution self-assembly has been studied. Using a combination of neutron reflectivity, NR, and small angle neutron scattering, SANS, the effect of mixing an isomer with a short symmetric hydrocarbon chain with one which has an asymmetric hydrocarbon chain on both the equilibrium surface adsorption behavior and the solution microstructure of the mixtures, both in the presence and absence of a divalent cation (Ca(2+)), has been investigated. In the absence of electrolyte, the LAS isomer mixtures form small charged globular micelles throughout the composition range studied. The micelle aggregation number increases with the increase in the asymmetric isomer content, reflecting an increase in the packing efficiency within the micelle. The addition of calcium ions promotes the formation of planar aggregates, as multilamellar vesicles, but only when the symmetric LAS isomer is the major component of the mixture. At a surfactant concentration just above the critical micelle concentration, CMC, and in the absence of electrolyte, the variation in the surface composition is close to the solution composition. Regular solution theory, RST, calculations show that this variation is also close to what is expected for ideal mixing. The addition of Ca(2+) ions induces a different surface behavior, resulting in the formation of multilayer structures at the interface throughout the entire composition range.