Development and characterization of essential oil component-based polymer films: a potential approach to reduce bacterial biofilm

The development of new polymeric materials aimed to control the bacterial biofilm appears to be an important practical approach. The goal of the present study was to prepare and characterize poly(ethylene-co-vinyl acetate) copolymer (EVA) films containing citronellol, eugenol, and linalool and evaluate their efficiency on growth and biofilm formation of Listeria monocytogenes, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa in monospecies and dual species. The results showed that the addition of oil components influenced the elastic modulus (15 % decrease), the tensile stress (30 % decrease), the elongation at break (10 % increase), and the contact angle values (10–20° decrease) while leaving the homogeneity of the surface unaltered. Among the polymeric films, EVA + citronellol and EVA + eugenol at 7 wt% had the best inhibitory effect. After 24–48 h of incubation, EVA + citronellol was more effective against the growth (30–60 % reduction) than EVA + eugenol (15–30 % inhibition). However, this inhibition decreased after 240 h of incubation. On the contrary, the biofilm evaluation revealed a strong inhibition trend also after prolonged incubation time: the amount of biomass per square centimeter formed on copolymer with oil components was significantly less (40–70 % decrease) than that on pure copolymer control for L. monocytogenes, S. aureus, and E. coli. When polymeric materials were simultaneously inoculated with combinations of S. aureus and E. coli, the biomass accumulated was higher for EVA + citronellol and lower for EVA + eugenol than that in monoculture biofilm. The findings were similar to the results obtained by 2,3-bis[2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide assay that measures the metabolic activity of viable cells.     

Synergistic antibacterial activity of the essential oil of Cuminum cyminum L. seed and nisin in a food model

Aims: To investigate effects of various concentrations of the essential oil of Cuminum cyminum L. seed alone and in combination with nisin on survival of vegetative forms of Bacillus cereus and Bacillus subtilis in a food model (commercial barley soup) and their ultrastructure. Methods and Results: Gas chromatography–mass spectrometry analysis indicated that cumin aldehyde (29·02%) and α‐terpinen‐7‐al (20·70%) constituted the highest amount of the essential oil. The lowest concentration of the essential oil significantly affected the growth of the bacteria at 8°C but not at 25°C. Synergistic effect of the essential oil in combination with the lowest concentration of nisin was observed on the bacteria at 8°C. Evaluation of the sensory properties showed that concentration of 0·15 μl ml^?1 of the essential oil was the most acceptable. Conclusions: The essential oil of C. cyminum L. seed showed the most bactericidal effects on B. cereus at 8°C. Ultrastructural studies of vegetative cells confirmed the synergistic destructive effects of the essential oil and nisin on membrane and cell wall of the bacteria. Significance and Impact of the Study: Utilization of essential oil of C. cyminum L. seed in combination with nisin can inhibit growth of food‐borne pathogens in food.     

Anti-biofilm properties of Satureja hortensis L. essential oil against periodontal pathogens

Essential oils of several plants are widely used in ethnomedicine for their antimicrobial and anti-inflammatory properties. However, very limited data exist on their use in connection to periodontal diseases. The aim of the present study was to investigate the bacterial growth inhibiting and anti-biofilm effects of Satureja hortensis L. (summer savory), Salvia fruticosa M. (sage), Lavandula stoechas L. (lavender), Myrtus communis L., and Juniperus communis L. (juniper) essential oils. Chemical compositions of the essential oils were analyzed by gas chromatography–mass spectrometry, minimum inhibitor concentrations (MICs) with the agar dilution method, and anti-biofilm effects by the microplate biofilm assay. The toxicity of each essential oil was tested on cultured keratinocytes. Of the 5 essential oils, S. hortensis L. essential oil had the strongest growth inhibition effect. Subinhibitory dose of S. hortensis L. essential oil had anti-biofilm effects only against Prevotella nigrescens. Essential oils did not inhibit keratinocyte viability at the concentrations of 1 and 5 μl/ml, however at the concentration of 5 μl/ml epithelial cells detached from the culture well bottom. The present findings suggest that S. hortensis L. essential oil inhibits the growth of periodontal bacteria in the concentration that is safe on keratinocytes, however, in the subinhibitory concentration its anti-biofilm effect is limited.     

Chemical composition and mosquito repellency of essential oil of Conyza newii propagated in different geographical locations of Kenya

Previously, essential oil of Conyza newii (Asterale: Asteracea, Oliv. & Hiern) growing in the northern part of West Pokot (35°E, 1°N) of Kenya was shown to be highly repellent [RD₅₀ = 8.9 × 10^?5 mg/cm², 95% confidence interval (CL)] to Anopheles gambiae s.s. Fumigant toxicity of the oil to the mosquito was also demonstrated. The major constituents of the oil were found to be monoterpenoids, including (S)‐(‐)‐perillyl alcohol, (S)‐(‐)‐perillaldehyde, geraniol, (R)‐(+)‐limonene, trans‐β‐ocimene and 1,8‐cineol. In this study, the chemical composition and repellency of essential oils of the plant seedlings collected from West Pokot (35°E, 1°N) and propagated in seven different geographical regions of Kenya [West Pokot (35°E, 1°N), Kilome (37°E, 1°S), Naivasha (36°E, 0°), Webuye (34°E, 1°N), Nyakach (34°E, 0°), Kericho (35°E, 0°) and Nairobi (36°E, 1°S)] were compared. There were significant variations (P < 0.01, 95% CL) in the relative proportions of the six constituents and this was reflected in the repellency of the essential oils (P < 0.01, 95% CL). Higher repellency of the oil was associated with greater proportions of (S)‐(‐) perillyl alcohol, (S)‐(‐)‐perillaldehyde and geraniol, and lower repellency was associated with an increased proportion of (R)‐(+)‐limonene. The results suggest significant epigenetic (chemotypic) variations in the repellency and composition of C. newii essential oils growing in different regions of Kenya.     

Thermostable xylanase inhibits and disassembles Pseudomonas aeruginosa biofilms

Pseudomonas aeruginosa biofilms are problematic and play a critical role in the persistence of chronic infections because of their ability to tolerate antimicrobial agents. In this study, various cell-wall degrading enzymes were investigated for their ability to inhibit biofilm formation of two P. aeruginosa strains, PAO1 and PA14. Xylanase markedly inhibited and detached P. aeruginosa biofilms without affecting planktonic growth. Xylanase treatment broke down extracellular polymeric substances and decreased the viscosity of P. aeruginosa strains. However, xylanase treatment did not change the production of pyochelin, pyocyanin, pyoverdine, the Pseudomonas quinolone signal, or rhamnolipid. In addition, the anti-biofilm activity of xylanase was thermally stable for > 100 days at 45°C. Also, xylanase showed anti-biofilm activity against one methicillin-resistance Staphylococcus aureus and two Escherichia coli strains.     

Peracetic acid activity on biofilm formed by Escherichia coli isolated from an industrial water system

One of the major problems in industrial water systems is the generation of biofilm, which is resistant to antimicrobial agents and causes failure of sanitization policy. This work aimed to study the anti-biofilm activity of peracetic acid (PAA) at contact times and temperatures combinations. To this end, a 96-well microtiter-based calorimetric method was applied in in vitro biofilm production using Escherichia coli, isolated from the water supply system of a pharmaceutical plant. The phenotypic and phylogenetic tests confirmed that the isolated bacteria belong to strains of Escherichia coli. The anti-biofilm activity of peracetic acid on formed biofilm was investigated at concentrations of 0·15–0·5% for a contact time of 5–15 min at 20–60°C. The maximum biofilm formation by MTP method using an Escherichia coli isolate was achieved in 96-h incubation in TSB containing wells at 37°C. Biofilm formation rate shown to be high by the environmental isolate compared with that of standard strain. PAA at concentrations above 0·25%, the temperature of 40°C and a minimum of 10 min of contact time was effective in the eradication of biofilm in an MTP-based system.     

A combination of ellagic acid and tetracycline inhibits biofilm formation and the associated virulence of Propionibacterium acnes in vitro and in vivo

Propionibacterium acnes is an opportunistic pathogen which has become notorious owing to its ability to form a recalcitrant biofilm and to develop drug resistance. The current study aimed to develop anti-biofilm treatments against clinical isolates of P. acnes under in vitro and in vivo conditions. A combination of ellagic acid and tetracycline (ETC; 250 μg ml^?1 + 0.312 μg ml^?1) was determined to effectively inhibit biofilm formation by P. acnes (80–91%) without affecting its growth, therefore potentially limiting the possibility of the bacterium attaining resistance. In addition, ETC reduced the production of extracellular polymeric substances (EPS) (20–26%), thereby making P. acnes more susceptible to the human immune system and antibiotics. The anti-biofilm potential of ETC was further substantiated under in vivo conditions using Caenorhabditis elegans. This study reports a novel anti-biofilm combination that could be developed as an ideal therapeutic agent with broad cosmeceutical and pharmaceutical applicability in the era of antibiotic resistance.     

Control of biofilm formation by poly-ethylene-co-vinyl acetate films incorporating nisin

The aim of this study was to evaluate the effect of poly-ethylene-co-vinyl acetate (EVA) films incorporating different concentrations (0.1%, 0.5% and 1%) of nisin on the biofilm-forming ability of Listeria monocytogenes ATCC 7644, Staphylococcus aureus 815 and Staphylococcus epidermidis ATCC 35984. Nisin was incorporated into two grades of EVA (EVA14 and EVA28) in the melt during a common film-blowing operation. The efficacy of EVA/nisin films was evaluated by biofilm biomass measurements and Live/Dead staining in combination with fluorescence microscopy. In order to evaluate whether the nisin incorporation could modify the film surface properties, contact angle measurements and scanning electron microscopy were performed. The results revealed the efficacy of EVA14/nisin films in reducing biofilm formation on their surfaces with more evident effect for S. epidermidis than L. monocytogenes and S. aureus strains. In contrast, EVA28/nisin films showed unsatisfactory activity. Fluorescence microscopy confirmed poor biofilm formation on EVA14/nisin films, also characterised by the presence of dead cells. The data presented in this study offer new potential applications for developing strategies aimed to improve the effect of antimicrobial agents.     

Inhibitory effects of the essential oils α-longipinene and linalool on biofilm formation and hyphal growth of Candida albicans

Candida albicans is one of the most common fungal pathogens, and causes systemic and invasive infections in humans. C. albicans biofilms are composed of yeast and hyphal and pseudohyphal elements, and the transition of yeast to the hyphal stage could be a virulence factor. In this study, diverse essential oils were initially investigated for anti-biofilm activity against C. albicans strains, and cascarilla bark oil and helichrysum oil and their components α-longipinene (a major constituent of both) and linalool were found to markedly inhibit biofilm formation without affecting planktonic cell growth. Moreover, α-longipinene and linalool were found to synergistically reduce biofilm formation. Notably, treatments with cascarilla bark oil, helichrysum oil, α-longipinene, or linalool clearly inhibited hyphal formation, and this appeared to be largely responsible for their anti-biofilm effect. Furthermore, the two essential oils, α-longipinene and linalool, reduced C. albicans virulence in Caenorhabditis elegans.     

Lack of induction of direct protection or cross-protection in Staphylococcus aureus by sublethal concentrations of Origanum vulgare L. essential oil and carvacrol in a meat-based medium

The capacity of Origanum vulgare L. essential oil (OVEO) and its majority compound, carvacrol (CAR), to induce direct tolerance and cross-tolerance in Staphylococcus aureus against high temperature (45 °C), lactic acid (pH 5.2) and NaCl (10 g/100 mL) was assessed. Overnight exposure of S. aureus to sublethal concentrations (1/2 MIC, 1/4 MIC) of either OVEO or CAR in meat broth revealed no induction of direct protection. S. aureus cells pre-adapted to OVEO or CAR showed no induction of cross-protection to high temperature, lactic acid or NaCl. Cells subjected to 24 h cycles of adaptation in increasing amounts (1/2 MIC to 2 × MIC) of OVEO or CAR showed no increase in direct tolerance. These results revealed a lack of induction of direct protection or cross-protection in S. aureus exposed to sublethal amounts of OVEO or CAR in meat-based broth, as determined by monitoring cell survival and growth behavior.     

The effects of temperature and shading on mortality and development rates of Aedes aegypti (Diptera: Culicidae)

Urbanization has caused an increase in favorable habitats for Aedes aegypti (Diptera: Culicidae), given their ability to reproduce in small and often non‐degradable artificial water‐containers. While much work has been done on Ae. aegypti biology and ecology in urban landscapes, the role of shading on immature stages as an independent factor from temperature, and any possible interactions between these factors, remains unexamined. We assessed how temperature and shading affected egg hatch‐rate, larval/pupal mortality, and larval development to adult stage under different factorial temperature (28; 31; 34; 37; 40° C) and shade (0%, 3,100 lux; 40%, 1,860 lux; 75%, 775 lux; 100%, 0 lux) regimes. Hatch‐rate was significantly lower at 37° C (57 %), and no eggs hatched at 40° C. There was no significant effect caused by shading on hatchability. Larval and pupal mortality at 37° C was significantly higher (35%) compared to lower temperature groups, while the effects of shading were emergent at low temperatures. Developmental times from hatching to adult emergence were significantly reduced with increasing temperatures and with greater light exposures. The eco‐physiological response of Ae. aegypti larvae to temperature and light regimes suggest a photosensitivity previously unstudied in this species.     

Biodegradation of Petroleum Hydrocarbons in Seawater at Low Temperatures (0–5 °C) and Bacterial Communities Associated with Degradation

In this study biodegradation of hydrocarbons in thin oil films was investigated in seawater at low temperatures, 0 and 5 °C. Heterotrophic (HM) or oil-degrading (ODM) microorganisms enriched at the two temperatures showed 16S rRNA sequence similarities to several bacteria of Arctic or Antarctic origin. Biodegradation experiments were conducted with a crude mineral oil immobilized as thin films on hydrophobic Fluortex adsorbents in nutrient-enriched or sterile seawater. Chemical and respirometric analysis of hydrocarbon depletion showed that naphthalene and other small aromatic hydrocarbons (HCs) were primarily biodegraded after dissolution to the water phase, while biodegradation of larger polyaromatic hydrocarbons (PAH) and C₁₀–C₃₆ n-alkanes, including n-hexadecane, was associated primarily with the oil films. Biodegradation of PAH and n-alkanes was significant at both 0 and 5°C, but was decreased for several compounds at the lower temperature. n-Hexadecane biodegradation at the two temperatures was comparable at the end of the experiments, but was delayed at 0°C. Investigations of bacterial communities in seawater and on adsorbents by PCR amplification of 16S rRNA gene fragments and DGGE analysis indicated that predominant bacteria in the seawater gradually adhered to the oil-coated adsorbents during biodegradation at both temperatures. Sequence analysis of most DGGE bands aligned to members of the phyla Proteobacteria (Gammaproteobacteria) or Bacteroidetes. Most sequences from experiments at 0°C revealed affiliations to members of Arctic or Antarctic consortia, while no such homology was detected for sequences from degradation experiment run at 5°C. In conclusion, marine microbial communities from cold seawater have potentials for oil film HC degradation at temperatures ≤5°C, and psychrotrophic or psychrophilic bacteria may play an important role during oil HC biodegradation in seawater close to freezing point.     

The toxicity and synergistic effects of alkyl-succinate oil on the first nymphal instars of the citrus cottony scale,Pulvinaria aurantii Cock. (Hem.: Coccidae)

The citrus cottony scale, Pulvinaria aurantii Cock. (Hem.: Coccidae) is one of the most important citrus pests in Iran. This study investigated the toxicity and synergistic effects of organophosphorous insecticides (Malathion, Chlorpyrifos, Buprofezin and DG oil) on first nymphal instars of P. aurantii in the laboratory conditions (25?±?1?°C, 75?±?5% RH and 16L:8D photoperiod). The values of LC₅₀ for Malathion, Chlorpyrifos and Buprofezin insecticides on the first nymphal instars were calculated as 76.90, 105.25 and 24.70?ppm, respectively. Also, results indicated that Buprofezin and Pyriproxifen are the most effective insecticides on first nymphal instars of P. aurantii. The values of LC₅₀ for each insecticide without oil and in half dose along with DG oil were equal. This was an indication for synergism role of DG oil combination. The results of this study showed that DG oil not only decreases the consumption of insecticides, but also increases their efficacy.     

Enhanced Nucleation of Atomic Layer Deposited Contacts Improves Operational Stability of Perovskite Solar Cells in Air

Metal‐halide perovskites show promise as highly efficient solar cells, light‐emitting diodes, and other optoelectronic devices. Ensuring long‐term stability is now a major priority. In this study, an ultrathin (2 nm) layer of polyethylenimine ethoxylated (PEIE) is used to functionalize the surface of C₆₀ for the subsequent deposition of atomic layer deposition (ALD) SnO₂, a commonly used electron contact bilayer for p–i–n devices. The enhanced nucleation results in a more continuous initial ALD SnO₂ layer that exhibits superior barrier properties, protecting Cs_0.25FA_0.75Pb(Br_0.20I_0.80)₃ films upon direct exposure to high temperatures (200 °C) and water. This surface modification with PEIE translates to more stable solar cells under aggressive testing conditions in air at 60 °C under illumination. This type of “built‐in” barrier layer mitigates degradation pathways not addressed by external encapsulation, such as internal halide or metal diffusion, while maintaining high device efficiency up to 18.5%. This nucleation strategy is also extended to ALD VO_x films, demonstrating its potential to be broadly applied to other metal oxide contacts and device architectures.     

Synthesis,antimicrobial, anti-biofilm evaluation,and molecular modelling study of new chalcone linked amines derivatives

A series of amide chalcones conjugated with different secondary amines were synthesised and characterised by different spectroscopic techniques ¹H NMR, ¹³C NMR, and ESI-MS. They were screened for in vitro antibacterial activity. Compounds 36, 37, 38, 42, and 44 are the most active among the synthesised series exhibiting MIC value of 2.0–10.0?µg/ml against different bacterial strains. Compound 36 was equipotent to the standard drug Ampicillin displaying MBC value of 2.0?µg/ml against the bacterial strain Staphylococcus aureus. The products were screened for anti-biofilm activity. Compounds 36, 37, and 38 exhibited promising anti-biofilm activity with IC₅₀ value ranges from 2.4 to 8.6?µg. Molecular modelling was performed suggesting parameters of signalling anti-biofilm mechanism. AspB327 HisB340 (arene–arene interaction) and IleB328 amino acid residues seemed of higher importance to inhibit c-di-GMP. Hydrophobicity may be crucial for activity. ADME calculations suggested that compounds 36, 37, and 38 could be used as good orally absorbed anti-biofilm agents.     

The Potentiality of Free Gram-negative Bacteria for Removing Oil and Grease from Contaminated Industrial Effluents

Summary Eight bacterial species were isolated from vegetable oil and grease-contaminated industrial wastewater, only four of which were found to have the ability to degrade oil and grease in the contaminated wastewater. These isolates were identified according to morphological and biochemical profiles as, Pseudomonas sp. (L1), P. diminuta (L2), P. pseudoalcaligenes (L3), and Escherichia sp. (L5). The degradative capabilities of the identified bacterial isolates for Tween 20 (Tw20) were investigated under different pH levels (6.5, 7, 7.5, and 8), different temperatures (30 and 37 °C) and different concentrations of Tw20 (1, 1.5, and 2%). Results revealed differences in their optimum conditions for maximum degradation of vegetable oil. Bacterial isolates were tested individually or in combinations using synthetic aqueous medium supplemented with 1% palm oil, incubated at 30 °C, and agitated at 150 rev/min for 13 days. All the tested bacteria were able to degrade the palm oil completely and utilized the free fatty acids (FFA) as a carbon source. The combination M1 (Pseudomonas sp. and P. diminuta) produced the highest degradative activity, followed by M3 (Pseudomonas sp., P. diminuta and P. pseudoalcaligenes). Also M1 produced the highest activity in reducing COD (93%) and BOD₅ (100%).     

Stability Assessment of Injectable Castor Oil-Based Nano-sized Emulsion Containing Cationic Droplets Stabilized by Poloxamer–Chitosan Emulsifier Films

The objectives of the present work were to prepare castor oil-based nano-sized emulsion containing cationic droplets stabilized by poloxamer–chitosan emulgator film and to assess the kinetic stability of the prepared cationic emulsion after subjecting it to thermal processing and freeze–thaw cycling. Presence of cryoprotectants (5%, w/w, sucrose +5%, w/w, sorbitol) improved the stability of emulsions to droplet aggregation during freeze–thaw cycling. After storing the emulsion at 4°C, 25°C, and 37°C over a period of up to 6 months, no significant change was noted in mean diameter of the dispersed oil droplets. However, the emulsion stored at the highest temperature did show a progressive decrease in the pH and zeta potential values, whereas the emulsion kept at the lowest temperatures did not. This indicates that at 37°C, free fatty acids were formed from the castor oil, and consequently, the liberated free fatty acids were responsible for the reduction in the emulsion pH and zeta potential values. Thus, the injectable castor oil-based nano-sized emulsion could be useful for incorporating various active pharmaceutical ingredients that are in size from small molecular drugs to large macromolecules such as oligonucleotides.     

Activity of sodium trimetaphosphate,associated or not with fluoride,on dual-species biofilms

Abstract

A response surface methodology was used to build a model to predict reductions in uropathogenic Escherichia coli biofilms in response to three compounds: cranberry extract [CB] at 3.0–9.0%, and caprylic acid [CAR] and thymol [TM] at 0.01%–0.05%. The predictive model for microbial reduction had a high regression coefficient (R²?=?0.9988), and the accuracy of the model was verified (R²?=?0.9527). Values of CAR, TM, and the quadratic term CAR² were the most significant (P?10 reduction) determined by ridge analysis were 8.3% CB +0.04% CAR +0.04% TM at 37?°C for 1?min. The model could be used to predict the most cost-efficient amounts of antimicrobial agents for anti-urinary tract infection products such as catheter lock solution and antimicrobial coatings for catheters.     

Influence of Temperature and Relative Humidity on Germinability of Mucor piriformis Spores

Studies were conducted to determine the influence of temperature and relative humidity (RH) on germinability and viability of Mucor piriformis spores. Spores did not survive when stored at 35 °C and their survival rate decreased rapidly at 30 °C; however, spores remained viable for more than 1 year at 0 °C. RH also significantly affected spore viability. Spores held at 26 °C and 100% RH no longer germinated after 35 days, while those held at 75 or 90% RH germinated for 65 days. At 20 °C, RH had little effect on spore germinability. The effect of temperature and RH on percentage spore germination also varied. At all temperatures studied, spore viability decreased more rapidly with time at 100% RH than at 75 or 90% RH. The least favorable, temperature-humidity combination, 30 °C and 100% RH, decreased spore germination from 100% to less than 1% in 14 days.     

Isolation of the crude oil degrading marine Acinetobacter sp. E11

The Acinetobacter sp. E11, isolated from Port Dickson Beach, Malaysia, was able to grow in media containing crude oil as the sole carbon and energy source. Substrate specificity studies showed that the bacterium exhibited substrate preference as growth was observed only in media containing aliphatic hydrocarbons, while aromatic and cyclic hydrocarbons inhibited growth. With the aliphatic hydrocarbons, growth was seen only in the long-chain alkanes tested (pentadecane, dodecane and hexadecane). No growth was recorded in the short-chain alkanes (pentane, hexane and heptane) tested. With complex hydrocarbons, only crude oil and 4T SHELL engine oil supported growth. No growth was observed in kerosene and PETRONAS gasoline. The isolate could grow in up to 10% and 20% [v/v] of the crude oil and alkanes tested, respectively. Among the long-chain alkanes tested, hexadecane was the most preferred, followed by pentadecane and dodecane. Nitrogen and phosphorous supplements were essential for growth and the best growth was achieved with 3% nitrogen/phosphorous additions. Microscopic observation revealed that the bacterium adhered to the hexadecane and crude oil droplets. GC analysis showed that the bacterium was able to degrade more than 60% of the hydrocarbons in the crude oil in 15 days at 37°C compared to the uninoculated media.