Antimicrobial mechanism of action of surfactant lipid preparations in enteric Gram-negative bacilli

NB-002, a novel nanoemulsion with broad antifungal activity against dermatophytes, other filamentous fungi, and Candida albicans

NB-002 is an oil-in-water emulsion designed for use for the treatment of skin, hair, and nail infections. The activity of NB-002 was compared to the activities of the available antifungal drugs against the major dermatophytes responsible for cutaneous infections, Trichophyton rubrum, Trichophyton mentagrophytes, Epidermophyton floccosum, and Microsporum spp., as well as 12 other genera of filamentous fungi. NB-002 consistently displayed fungicidal activity against all dermatophytes. The comparator compounds were either fungistatic or fungicidal, and for some strain-drug combinations, tolerance was observed. Assessment of the development of spontaneous resistance to NB-002 in different dermatophyte species yielded few stably resistant mutants. For filamentous nondermatophyte fungi, the MIC range varied from 0.06 to 0.5 microg/ml for Alternaria spp. to 2 to 8 microg/ml for Paecilomyes spp. NB-002 had activity against both azole-susceptible and -resistant Candida albicans yeast isolates, with MIC(90)s of 2 microg/ml, respectively, and minimum fungicidal concentrations at which 90% of isolates are inhibited of 4 and 8 microg/ml, respectively. The kinetics of the fungicidal activity of NB-002 against T. rubrum isolates were compared to those of the other antifungal drugs. NB-002 killed both mycelia and microconidia even when the fungal forms were dormant or not actively growing. Electron micrographs of mycelia and spores treated with NB-002 showed the significant disruption of the fungal structure. The in vitro broad coverage of NB-002 against filamentous fungi, dermatophytes, and C. albicans, as well as its rapid fungicidal activity, warrants further investigations to ascertain if NB-002 would be useful for the treatment of cutaneous mycoses.

In vitro activities of a novel nanoemulsion against Burkholderia and other multidrug-resistant cystic fibrosis-associated bacterial species

Respiratory tract infection, most often involving opportunistic bacterial species with broad-spectrum antibiotic resistance, is the primary cause of death in persons with cystic fibrosis (CF). Species within the Burkholderia cepacia complex are especially problematic in this patient population. We investigated a novel surfactant-stabilized oil-in-water nanoemulsion (NB-401) for activity against 150 bacterial isolates recovered primarily from CF respiratory tract specimens. These specimens included 75 Burkholderia isolates and 75 isolates belonging to other CF-relevant species including Pseudomonas, Achromobacter, Pandoraea, Ralstonia, Stenotrophomonas, and Acinetobacter. Nearly one-third of the isolates were multidrug resistant, and 20 (13%) were panresistant based on standard antibiotic testing. All isolates belonging to the same species were genotyped to ensure that each isolate was a distinct strain. The MIC(90) of NB-401 was 125 microg/ml. We found no decrease in activity against multidrug-resistant or panresistant strains. MBC testing showed no evidence of tolerance to NB-401. We investigated the activity of NB-401 against a subset of strains grown as a biofilm and against planktonic strains in the presence of CF sputum. Although the activity of NB-401 was decreased under both conditions, the nanoemulsion remained bactericidal for all strains tested. These results support NB-401's potential role as a novel antimicrobial agent for the treatment of infection due to CF-related opportunistic pathogens.

Light-induced biocidal action of conjugated polyelectrolytes supported on colloids

A series of water soluble, cationic conjugated polyelectrolytes (CPEs) with backbones based on a poly(phenylene ethynylene) repeat unit structure and tetraakylammonium side groups exhibit a profound light-induced biocidal effect. The present study examines the biocidal activity of the CPEs, correlating this activity with the photophysical properties of the polymers. The photophysical properties of the CPEs are studied in solution, and the results demonstrate that direct excitation produces a triplet excited-state in moderate yield, and the triplet is shown to be effective at sensitizing the production of singlet oxygen. Using the polymers in a format where they are physisorbed or covalently grafted to the surface of colloidal silica particles (5 and 30 microm diameter), we demonstrate that they exhibit light-activated biocidal activity, effectively killing Cobetia marina and Pseudomonas aeruginosa. The light-induced biocidal activity is also correlated with a requirement for oxygen suggesting that interfacial generation of singlet oxygen is the crucial step in the light-induced biocidal activity.

Pre-clinical evaluation of a novel nanoemulsion-based hepatitis B mucosal vaccine

BACKGROUND

Hepatitis B virus infection remains an important global health concern despite the availability of safe and effective prophylactic vaccines. Limitations to these vaccines include requirement for refrigeration and three immunizations thereby restricting use in the developing world. A new nasal hepatitis B vaccine composed of recombinant hepatitis B surface antigen (HBsAg) in a novel nanoemulsion (NE) adjuvant (HBsAg-NE) could be effective with fewer administrations.

METHODOLOGY AND PRINCIPAL FINDINGS

Physical characterization indicated that HBsAg-NE consists of uniform lipid droplets (349+/-17 nm) associated with HBsAg through electrostatic and hydrophobic interactions. Immunogenicity of HBsAg-NE vaccine was evaluated in mice, rats and guinea pigs. Animals immunized intranasally developed robust and sustained systemic IgG, mucosal IgA and strong antigen-specific cellular immune responses. Serum IgG reached > or = 10(6) titers and was comparable to intramuscular vaccination with alum-adjuvanted vaccine (HBsAg-Alu). Normalization showed that HBsAg-NE vaccination correlates with a protective immunity equivalent or greater than 1000 IU/ml. Th1 polarized immune response was indicated by IFN-gamma and TNF-alpha cytokine production and elevated levels of IgG(2) subclass of HBsAg-specific antibodies. The vaccine retains full immunogenicity for a year at 4 degrees C, 6 months at 25 degrees C and 6 weeks at 40 degrees C. Comprehensive pre-clinical toxicology evaluation demonstrated that HBsAg-NE vaccine is safe and well tolerated in multiple animal models.

CONCLUSIONS

Our results suggest that needle-free nasal immunization with HBsAg-NE could be a safe and effective hepatitis B vaccine, or provide an alternative booster administration for the parenteral hepatitis B vaccines. This vaccine induces a Th1 associated cellular immunity and also may provide therapeutic benefit to patients with chronic hepatitis B infection who lack cellular immune responses to adequately control viral replication. Long-term stability of this vaccine formulation at elevated temperatures suggests a direct advantage in the field, since potential excursions from cold chain maintenance could be tolerated without a loss in therapeutic efficacy.

What can be inferred from bacterium-nanoparticle interactions about the potential consequences of environmental exposure to nanoparticles?

This article collates published information regarding the in vitro antibacterial activity of both metal and carbon nanoparticles. The aims are to establish a consensus regarding modes of antibacterial activity, and to evaluate the applicability of current knowledge to prediction of likely effects of nanoparticles upon important microbial processes in environmental exposures. The majority of studies suggest that nanoparticles cause disruption to bacterial membranes, probably by production of reactive oxygen species. Contact between the nanoparticle and bacterial membrane appears necessary for this activity to be manifested. Interfacial forces such as electrostatic interactions are probably important in this respect. However, the toxicity of free metal ions originating from the nanoparticles cannot be discounted. Passage of nanoparticles across intact membranes appears to be unlikely, although accumulation within the cytoplasm, probably after membrane disruption, is often observed. To date, published studies have not been designed to mimic natural systems and therefore provide poor understanding of the likely consequences of intentional or unintentional environmental release. The limited studies currently available fail to identify any significant effects at the microbial level of nanoparticles in more complex systems.

Antimicrobial effects of a microemulsion and a nanoemulsion on enteric and other pathogens and biofilms

Some microemulsions and nanoemulsions may have antimicrobial properties and be effective anti-biofilm agents. We examined the abilities of two fine emulsions, designated BCTP and TEOP, to inactivate suspensions of vegetative cells of Salmonella spp. Escherichia coli 0157:H7 (VT-), Pseudomonas aeruginosa, Staphylococcus aureus and Listeria monocytogenes. BCTP is an O/W nanoemulsion of soybean oil and tri-n-butyl phosphate emulsified with Triton X-100, while TEOP is an O/W microemulsion of ethyl oleate with Tween 80 as emulsifier and n-pentanol as a co-emulsifier. BCTP was effective in reducing the cell numbers of L. monocytogenes, while TEOP was effective against all five organisms investigated. The abilities of these emulsions to reduce preformed biofilms of the five bacteria were also investigated. With the exception of the biofilm formed by L. monocytogenes, which surprisingly was not significantly affected by BCTP, all biofilms were inhibited by both BCTP and TEOP.

Photocatalytic degradation of pathogenic bacteria with AgI/TiO2 under visible light irradiation

The photocatalytic disinfection of pathogenic bacteria in water was investigated systematically with AgI/TiO2 under visible light (lambda > 420 nm) irradiation. The catalyst was found to be highly effective in killing Escherichia coli and Staphylococcus aureus. The adsorbed *OH and hVB+ on the surface of the catalyst were proposed to be the main active oxygen species by study of electron spin resonance and the effect of radical scavengers. The process of destruction of the cell wall and the cell membrane was verified by TEM, potassium ion leakage, lipid peroxidation, and FT-IR measurements. Some products from photocatalytic degradation of bacteria such as aldehydes, ketones, and carboxylic acids were identified by FT-IR spectroscopy. These results suggested that the photocatalytic degradation of the cell structure caused the cell death. The electrostatic force interaction of the bacteria-catalyst significantly affected the efficiency of disinfection on the basis of the E. coli inactivation under different conditions.

Simple and double emulsions via coaxial jet electrosprays

We report for the first time the generation of electrified coaxial jets of micrometric diameter in liquid media. Scaling laws to predict the inner and outer diameter of the coaxial jet are given. We show some experiments illustrating the formation process of the coaxial jet, and demonstrate how this process can be used to yield either o/w (oil in water) or o/w/o (oil/water/oil) emulsions of micrometric size. Some interesting analogies with other hydrodynamic focusing processes are also pointed out.

Efficient destruction of pathogenic bacteria with NiO/SrBi2O4 under visible light irradiation

The photocatalytic inactivation of pathogenic bacteria in water was investigated systematically with NiO/SrBi2O4 under visible light (lambda > 420 nm) irradiation. The catalyst was found to be highly effective in killing Escherichia coli, a Gram-negative bacterium, and Staphylococcus aureus, a Gram-positive bacterium. ESR studies revealed that *OH and O2*- were involved as the active species in the photocatalytic reaction. The decomposition process of the cell wall and the cell membrane was directly observed byTEM and further confirmed by the determination of potassium ion (K+) leakage from the killed bacteria. A possible cell damage mechanism by visible-light-driven NiO/SrBi2O4 is proposed. In addition, the effects of pH, methanol, and inorganic ions on bacterial photocatalytic inactivation were investigated. These results indicated that the electrostatic force interaction of bacteria-catalyst is crucial for high bactericidal efficiency.

Biocidal activity of a light-absorbing fluorescent conjugated polyelectrolyte

Herein we describe studies that indicate a cationic conjugated polyelectrolyte shows biocidal activity against gram-negative bacteria (Escherichia coli, E. coli, BL21, with plasmids for Azurin and ampicillin resistance) and gram-positive bacterial spores (Bacillus anthracis, Sterne, B. anthracis, Sterne). These studies were carried out with aqueous suspensions of the conjugated polyelectrolyte, with the polyelectrolyte in supported formats and with samples in which the conjugated polyelectrolyte was coated on the bacteria. The results are interesting in that the biocidal activity is light-induced and appears effective due to the ability of the conjugated polyelectrolyte to form a surface coating on both types of bacteria. The effects observed here should be general and suggest that a range of conjugated polyelectrolytes in different formulations may provide a useful new class of biocides for both dark and light-activated applications.

Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria

The antimicrobial activity of silver nanoparticles against E. coli was investigated as a model for Gram-negative bacteria. Bacteriological tests were performed in Luria-Bertani (LB) medium on solid agar plates and in liquid systems supplemented with different concentrations of nanosized silver particles. These particles were shown to be an effective bactericide. Scanning and transmission electron microscopy (SEM and TEM) were used to study the biocidal action of this nanoscale material. The results confirmed that the treated E. coli cells were damaged, showing formation of "pits" in the cell wall of the bacteria, while the silver nanoparticles were found to accumulate in the bacterial membrane. A membrane with such a morphology exhibits a significant increase in permeability, resulting in death of the cell. These nontoxic nanomaterials, which can be prepared in a simple and cost-effective manner, may be suitable for the formulation of new types of bactericidal materials.

Influence of ion accumulation on the emulsion stability and performance of semi-synthetic metalworking fluids

The metalworking industry is one of the largest in the United States. Although metalworking fluids (MWFs) are ubiquitous in manufacturing as coolants and lubricants, these emulsified fluids have a significant environmental impact over their life cycle. Accordingly, it has become necessary to better understand emulsion destabilization mechanisms that lead to MWF deterioration and disposal so that MWF formulations can be designed for increased longevity. This paper investigates the impact of pH and a wide range of hard water salts on MWF emulsion stability. While expected trends from the emulsion science literature are observed, it is shown that MWF destabilization can lead to an increase in the microbial load that the MWF can sustain while only slightly improving manufacturing performance as measured by the tapping torque test. Experimental observations also indicate that these trends are strongly correlated with increased emulsion particle size, regardless of whether increased particle size is achieved by aging, by reductions in pH, or by the addition of hard water salts. In MWF systems, these conditions typically result from the accumulation of divalent and trivalent cations over time due to hard water additions and exposure to metal workpieces and tools. While MWFs are formulated with EDTA to avoid emulsion destabilization due to cation accumulation, it is shown that EDTA can be ineffective or highly inefficient for this purpose due to direct interactions between EDTA and the MWF emulsifier system. Given the ineffectiveness of EDTA and commonly utilized MWF emulsifier systems to maintain stable emulsion size in the presence of high concentrations of hard water salts, a more effective and environmentally preferable technological change to the MWF formulation design is proposed and successfully demonstrated.

Steady cone-jet electrosprays in liquid insulator baths

This study shows that conducting liquids can be electrosprayed in steady cone-jet mode inside liquid insulator baths. Experimental results show that the current emitted from the meniscus fits well the scaling laws given in the literature for electrosprays in air at atmospheric pressure or vacuum. The technique may be of interest in obtaining fine liquid-liquid emulsions of uniformly sized droplets in the nanometric range.

A rapid staining technique for the detection of the initiation of germination of bacterial spores

AIMS

We propose to apply the Wirtz-Conklin staining technique to evaluate spore germination.

METHODS AND RESULTS

Spores at different stages of germination were stained with modified spore stain (Wirtz-Conklin) and evaluated for staining properties. Bacillus spores suspended in deionized water, which does not support germination, stained greenish-blue. Spores suspended in germination enhancers that did not form bacilli stained pink, indicating the initiation of germination. Spores suspended in culture media, which promotes bacterial outgrowth, formed bacilli and were also stained pink.

CONCLUSIONS

Modified spore stain (Wirtz-Conklin) was found to be useful to detect the initiation of spore germination as early as 30 min following incubation in a germination environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

This simple staining procedure is useful in detecting the initiation of germination of bacterial spores.

A novel surfactant nanoemulsion with a unique non-irritant topical antimicrobial activity against bacteria, enveloped viruses and fungi

A novel non-ionic surfactant nanoemulsion designated 8N8 has been tested for its biocidal activity. One percent 8N8 produced effective bactericidal activity against Bacillus cereus, Bacillus subtilis, Haemophilus influenzae, Neisseria gonorrhoeae, Streptococcus pneumoniae, and Vibrio cholerae in 15 minutes. In contrast, most enteric gram-negative bacteria were resistant to 8N8. One percent 8N8 was also virucidal within 15 minutes for all tested enveloped viruses, including Herpes simplex type 1, influenza A and vaccinia viruses. One percent 8N8 also demonstrated fungistatic activity on Candida albicans. The rapid and non-specific inactivation of vegetative bacteria and enveloped viruses, in addition to its fungistatic activity and low toxicity in experimental animals, makes 8N8 a potential candidate for use as a topical biocidal agent.