Inhibition Zone Method Research Articles

Preparation and characterization of carboxymethyl chitosan/polyvinyl alcohol composite hydrogel with improved mechanical and antibacterial properties

Biopolymer-based antibacterial hydrogels have attracted considerable interest in biomedical field. Herein, we report on an effective strategy for the preparation of carboxymethyl chitosan/polyvinyl alcohol (CMCh/PVA) composite hydrogel with improved mechanical and antibacterial properties by using poly(ethylene glycol) diglycidyl ether (PEGDE) as crosslinking agent and zinc acetate (ZnAc2) as catalyst, respectively. FT-IR and gelation time measurements confirm that the introduction of both PVA and ZnAc2 can accelerate the formation of ester bonds between CMCh and PEGDE. SEM images reveal the interconnected macroporous inner architecture in the current CMCh/PVA composite. While the hydrogels exhibit pH-sensitive swelling behaviors in the pH range from 3 to 11, they remain relatively stable in phosphate buffered saline buffer. Compression mechanical tests show that, when increasing the PVA concentration to 1.0%, the resultant CMCh/PVA composite hydrogel shows a compressive strength of 1.96 MPa. The dried composite sample prepared with 1.0% PVA has a water absorption capacity of 1860%. The antibacterial activities of the CMCh/PVA hydrogel are studied against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus by inhibition zone method, indicating that the composite hydrogel exhibits improved antibacterial activity after the adsorption of zinc ions.

Ointment Formulation of Arumanis Mango (Mangifera indica L.) Leaf Extract with Chitosan Tripoliphosphate Matrix as Antibacterial

This report presented the synthesis of Arumanis mango (Mangifera indica L.) leaf extract with chitosan tripolyphosphate matrix and its antibacterial activity. This research aimed to obtain an ointment formulation from mango leaf extract with chitosan tripolyphosphate matrix, to figure out the characteristics, including the particle morphology, and to determine the optimum formulation and the characterization of the antibacterial ointment. The research showed that extract morphology with chitosan tripolyphosphate was uneven-edge aggregates. Antibacterial tests were conducted on P. acnes and E. coli bacteria. The formula giving the greatest antibacterial activity was further utilized for the ointment preparations and then was characterized for 16 days. Formula C (chitosan and NaTPP 1: 0.0992(%)) gave the most excellent inhibition zone for P. acnes and E. Coli bacteria, at 7.94 mm and 10.02 mm, respectively. The obtained ointment preparation was white color homogeneous semi-solid with protective properties. The spreading power of the ointment was 5.25 – 6.25 cm, with the adhesive power of 1 – 5 seconds and pH of 6.0 – 6.4. The ointment's antibacterial activity was tested against P. acnes and E. coli bacteria using the formation of inhibition zone method. The activity of ointment prepared on day one against P. acnes and E. coli was at 14.03 mm and 14.24 mm, respectively, while the activity on day 16 against P. acnes and E. coli was at 9.33 mm and 9.98 mm, respectively.

In vitro screening of synbiotics composed of Lactobacillus paracasei VL8 and various prebiotics and mechanism to inhibits the growth of Salmonella Typhimurium

This study aimed to screen the synbiotics with good antibacterial effect against Salmonella Typhimurium and to investigate its antibacterial mechanism. Laboratory-isolated Lactobacillus paracasei VL8 were selected and combined with four prebiotics, fructooligosaccharide (FOS), inulin, galactooligosaccharide (GOS), and mannan oligosaccharide (MOS) for the comparison. Their growth, adhesion, tolerance and inhibition ability were evaluated by growth curve, non-specific adhesion test, simulated gastrointestinal fluid, and zone of inhibition method, respectively. The results showed that MOS had a better synbiotic effect with L. paracasei VL8, resulting in a significant increase in the growth of L. paracasei VL8, higher acid production, and a larger zone of inhibition of S. Typhimurium, reaching 16.75 mm. The time-kill curves showed that 20% (v/v) of metabolite in the medium could kill S. Typhimurium within 4h completely. Further, electron microscopic micrographs showed that the synbiotic metabolites caused damage to the cell membrane of S. Typhimurium, resulting in cytoplasmic efflux. The Findings indicated that the synbiotic combination between MOS and L. paracasei VL8 not only promoted the growth and acid production of the probiotic, but also exerted good inhibitory effects on S. Typhimurium by disrupting the cell membrane, which can be a potential natural antimicrobial agent for food applications.

Study on Extraction and Antibacterial Activity of Essential Oil from Liquidambar formosana Hance (L.) leaves by Continuous Flow Microreactor

As a natural medication and food plant resource, Liquidambar formosana Hance (L.) leaves are growing popularity in the fields of medicine and health care. The essential oil of L. leaves was extracted by continuous flow microreactor, and the extraction rate is 53.2%. 26 compounds from essential oil were identified by gas chromatography/mass spectrometry (GC/MS). The main components of these compounds are α-pinene, β-pinene and limonene. Ten of them are reported for the first time. The antibacterial activity of essential oil was investigated by the inhibition zone method, minimum inhibitory concentration and inhibition growth curve experiment. The results show that the essential oil had inhibitory effects on both Escherichia coli (E. coli) and Bacillus subtilis (B.subtilis), and the minimum inhibitory concentrations are 1.0 μg/mL and 1.2 μg/mL. The inhibition effect on gram-negative bacteria E.coli is stronger. The results of this study show that the essential oil contains rich medicinal value components and have great potential for exploitation. This research provided a scientific foundation for understanding essential oil while also providing a theoretical foundation for their full and rational utilization. Simultaneously, research into the antibacterial properties of essential oil provides a scientific basis for the further development of the anti-bacterial agents that exists in plants.

Antibacterial efficacy of a topical skin cream loaded with nano zinc oxide, cetylpyridinium chloride and chlorhexidine gluconate

Nano-based antimicrobial agents are rapidly growing due to their exceptional properties such as biodegradability, biocompatibility, and lower toxicity. On the contrary, commonly synthesized preservatives are more toxic and partially have undesirable side effects on human health and environment. In the present study, a prominent antimicrobial effect of nanoformulation was achieved by in-vitro assessment of five different clinical pathogens such as S. aureus, E. coli, P. aeruginosa, S. typhi, and Shigella along with Zone Inhibition method and time kill study. Penicillin was used as control where the maximum log reduction values reached to four log cycles in skin cream–C with 1.00 % nano zinc oxide (ZnO) and 0.30 % chlorhexidine gluconate (CHG) within 30 s of exposure. However, moderate log reduction was observed in skin cream–B with 1.00 % nano-ZnO and 0.30 % cetylpyridinium chloride (CPC), where the log reduction values reached to four and three log cycles within 30 s of exposure. In contrast, the lower log reduction values were noticed in skin cream–A with 1.00 % nano-ZnO, where the log reduction values reached to two and one log cycles. Thus, outcome of the study demonstrates that the antimicrobial agents (zinc oxide nanoparticles, CPC, and CHG) could be recommended as powerful candidates which exhibit antibacterial effect against bacterial strains in skin care formulations. This study also highlights the use of cream-based disinfectant containing ingredients that moisturizes the skin.

Controlled-Release of Plant Volatiles: New Composite Materials of Porous Carbon-Citral and Their Fungicidal Activity against Exobasidium vexans

Citral (Eo) exhibits excellent fungicidal activities. However, it is difficult to maintain long-term fungicidal activity due to its strong volatility. Herein, a controlled-release strategy by using biomass-derived porous carbon (BC) was developed to overcome the drawback of Eo. New composite materials were prepared by loading Eo on tea stem porous carbon (BC@Eo), and their controlled-release fungicidal activity against Exobasidium vexans was assessed. BC with a large specific surface area of 1001.6 m2/g and mesoporous structure was fabricated through carbonization temperature of 700°C. The BC@Eo materials were characterized using Fourier-transform infrared spectroscopy and X-ray powder diffraction. The results suggested that chemical and physical interactions occurred in BC@Eo. The Eo release profile suggested a biphasic pattern with an initial fast release on days 1–14 and a subsequent controlled phase on days 14–30. The in vitro cumulative release percentage of Eo from BC@Eo was 51% during one month, and this result was significantly lower than that from free Eo (cumulative release percentage of Eo of 82% in one week). The antifungal activities of Eo and BC@Eo against E. vexans were determined using the inhibition zone method. The results indicated that Eo and BC@Eo formed large inhibition zones of 19.66 ± 0.79 and 21.92 ± 0.77 mm, respectively. The influence on the hyphal structure of E. vexans was observed by scanning electron microscopy on day 30. The hyphal structure of E. vexans treated with BC@Eo was more shrunken than that treated with Eo at 30 days, suggesting that BC@Eo prolongs the fungicidal activity against E. vexans. This study demonstrated that the encapsulation of Eo in BC for developing the BC@Eo materials could be a promising strategy to inhibit volatility and maintain the fungicidal activity of Eo and provide a potential alternative for the reuse of abundant tea biomass waste resources.

Fabrication of Silver-Doped UiO-66-NH2 and Characterization of Antibacterial Materials

Metal-organic frameworks (MOFs) are highly crystalline inorganic-organic complexes formed from metal ions or metal clusters and multi-toothed organic ligands. MOFs have great potential for use in antibacterial materials in the biological, environmental, and food antimicrobial fields. They can act as a reservoir of metal ions, releasing them gradually and leading to a sustained antibacterial effect analogous to that proposed for metal oxide nanoparticles (NPs). Herein, UiO-66-NH2 as a type of MOF was first prepared by a facile solvothermal method and then loaded with Ag NPs to form a Ag/UiO-66-NH2 composite and the different materials were synthesized by controlling silver doping amount, which are then applied to an antibacterial test. Works on the synthesis of Ag/UiO-66-NH2 and its antibacterial test were not reported before. The synthesized materials were characterized using the field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), thermal gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) techniques. The antibacterial activity of the Ag/UiO-66-NH2 was then assessed against E. coli (gram-negative bacteria) and Staphylococcus aureus (gram-positive bacteria), using the inhibition zone (ZIO) method and optical density (OD) method. The obtained results have shown that the introduction of Ag does not interfere with the crystallization of UiO-66-NH2. The FT-IR spectral profiles recorded for the UiO-66-NH2 samples fabricated under conditions of varying silver ion doping levels are similar to those recorded for UiO-66-NH2. The thermal stability of UiO-66-NH2 containing varying amounts of silver ions was lower than the thermal stability of UiO-66-NH2. However, under these conditions, the specific surface area and pore volume increased. The antibacterial performance of UiO-66-NH2 improved significantly following the process of silver ion doping. The best antibacterial performance was observed when the silver ion content was 4 wt.%. Overall, we synthesized a new nanocomposite material with broad-spectrum bacterial sterilization, which was easy to manufacture.

Antimicrobial and Ion-exchange Properties of Layered KHSi<sub>2</sub>O<sub>5</sub> Compounds Prepared Using Amorphous Silicon Dioxide (a-SiO<sub>2</sub>) Blocks

A layered silicate, KHSi2O5, was synthesized via a hydrothermal method using an amorphous silicon dioxide (SiO2) block, which is industrial waste. This layered silicate was used as a host compound for ion-exchange reactions with Ag+ and Cu2+ ions, and the antibacterial properties of the ion-exchanged compounds were investigated. The crystal structures of the compounds were retained during the ion-exchange reaction; however, in the case of Cu2+, a small amount of Cu(OH)2 coexisted. The M/Si (where M is Ag or Cu) ratios of the ion-exchanged compounds were 0.03 - 0.50 and 0.01 - 0.32 for M = Ag and Cu, respectively. The antibacterial activity was analyzed by the inhibition zone method using two standard model bacteria: Staphylococcus aureus (S. aureus,gram-positive) and Escherichia coli (E. coli, gram-negative). The Ag-KHSi2O5 and Cu-KHSi2O5 samples showed good antibacterial activity owing to the release of Ag+ and Cu2+ ions from their host silicates. Here, the antibacterial activity of each sample were compared by relative antibacterial activity which was calculated based on the bacterial inhibition zone area. The antibacterial activity of Ag-KHSi2O5 against S. aureus was higher than that against E. coli, whereas the antibacterial activity of Cu-KHSi2O5 against S. aureus was lower than that against E. coli.

Green Synthesis of Gold Nanoparticles Using Polyphenols from Pomelo Leaves and its Antibacterial Properties

Gold nanoparticles (AuNPs) were synthesized by one-step reduction of chloroauric acid using pomelo leaf polyphenol extract as reducing and protective agent. The AuNPs were characterized by UV-Vis absorption spectroscopy. Compared with AuNPs prepared with sodium citrate as reducing agent, AuNPs prepared with pomelo leaf polyphenol extract had better stability. The antioxidant properties of green-synthesized AuNPs were investigated by Bland-Williams method. The antibacterial activity of the green synthesized AuNPs was investigated by the transparent inhibition zone method and the minimum inhibitory concentration method. The results showed that the AuNPs prepared with pomelo leaf polyphenol extract as biological template had good antioxidant activity. The scavenging rate of 1, 1-diphenyl-2-trinitrophenylhydrazide free radical (DPPH•) was 95.65% when the 1.0 g/L AuNPs solution was used. The antibacterial activity of AuNPs synthesized from pomelo leaf polyphenol extract against Staphylococcus aureus was higher than that of AuNPs synthesized chemically. The minimum inhibitory concentration of green synthesized AuNPs was 0.85 g/L, while the minimum inhibitory concentration of chemically synthesized AuNPs was 1.58 g/L.

Surface modification of poly(propylene) fabric with graphene oxide‐based silver nanoparticles for antibacterial applications

AbstractHerein, poly(propylene) (PP) was hydrophilized with oxidating agents and solvents, followed by dip‐coating with silver nanoparticles anchored GO sheets (Ag@GO) prepared by the in‐situ method as reported in our previous study to obtain silver@graphene oxide‐coated poly(propylene) (Ag@GO/PP). The impact of the modifying agents, dipping times, and coating concentrations on the antibacterial activities were studied accordingly via the inhibition zone method. The fabrics were re‐hydrophobized with the reduction of Ag@GO and the functionalization with stearic acid (SA) to form silver@reduced graphene oxide‐coated poly(propylene) (Ag@rGO/PP) and silver@graphene oxide/SA‐coated poly(propylene) (Ag@rGO‐SA/PP), respectively. Characterization of pretreated and modified PP samples was carried out by various modern analysis methods. Simultaneously, the cytotoxicity of the active layers, the release of Ag+ ions, and durability after washing were also investigated. The obtained results representing PP fabrics pretreated with HNO3/isopropanol and dipped in Ag@GO concentration of 2 g/L four times prove a sufficient approach for improving hydrophilization and bio‐compatibility for the PP samples. The fabrics greatly show an impressive interaction with precursors, mostly high antibacterial activity even after four washing cycles via appropriate releasing of Ag+ to ensure the safety in usage. They further suggest that the prepared fabrics could be utilized for actual application as a face mask.

Superhydrophobic sponge decorated with hydrophobic MOF-5 nanocoating for efficient oil-water separation and antibacterial applications

Increased discharge of industrial oily effluent threatens the environment and human health; thus, researchers are developing effective methods to separate oil from water. Recently, superhydrophobic surfaces with oil-water separation properties have received attention. In this study, we proposed a simple method to fabricate superhydrophobic/superoleophilic sponges decorated with zinc (Zn)-based metal-organic frameworks (MOF-5) with oil-water separation and antibacterial properties. The synthesized superhydrophilic MOF-5 nanoparticles were hydrophobized using low surface energy 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS) material. Finally, a simple dip-coating process was performed to prepare superhydrophobic sponge after altering hydrophobic MOF-5 (H-MOF-5) with polydimethylsiloxane (PDMS). The synergistic effect between the H-MOF-5 and low surface energy PDMS resulted in superhydrophobicity. The fabricated sponge showed water repellency with a high water contact angle (WCA) of 156° and a sliding angle (SA) of 6°. In addition, it exhibited extraordinary oil-water separation and antibacterial properties. Superhydrophobic sponges can be used to remove light or heavy oil-water mixtures using absorption under stirring and a gravity-driven separation approach, respectively. Continuous separation of various types of oil/organic solvent-water mixtures was demonstrated using a vacuum-assisted method with separation efficiency >98%. The sponge displayed exceptional reusability, maintaining a high separation efficiency of over 95% and retaining WCA at 153° after 10 cycles. The antibacterial property of the copper substrate modified with superhydrophobic PDMS@H-MOF-5 coating was investigated against Staphylococcus aureus bacteria using the inhibition zone method. In comparison to an uncoated copper surface, the superhydrophobic surface demonstrated significant bacterial resistance efficacy with a 30 mm zone of inhibition. The proposed approach offers new opportunities for preparing a superhydrophobic sponge with hydrophobic MOF-5 nanoparticles for various applications, including oil-spill cleaning and organic pollutant removal on water surfaces.

Acid-etched Halloysite nanotubes as superior carriers for ciprofloxacin

Clay minerals have opened new avenues in drug delivery, including antimicrobials, greatly enhancing the stability and efficacy of the active payloads. Among these clay mineral hosts, Halloysite nanotubes (HNT) have emerged as a prominent carrier owing to their intrinsic mesoporous tubular nanostructure and high adsorption capacity. The acidic etching of HNT increases their specific surface area and porosity, consequently enhancing their loading potential. In this work, we show for the first time, that etched HNT (E-HNT) are superior carriers of the potent antibiotic ciprofloxacin (CIP) compared to pristine HNT in terms of loading capacity and antibacterial effect. The loading conditions are optimized within near-physiological conditions to enable future combinations with biomolecules; where CIP loading and release are characterized by UV–Vis measurements and thermogravimetry. Solid-state characterization suggests an adsorptive loading mechanism, involving electrostatic attraction and possible tautomerism. Release experiments show that the loaded CIP exhibits a sustained release profile and maintains its antibacterial potency as confirmed by the broth microdilution (BMD) and zone of inhibition methods. Thus, the facile etching of HNT enhances the nanoclay properties rendering it suitable for future application in drug delivery formulations.

Performance of dodecyl dimethyl benzyl ammonium chloride as bactericide and corrosion inhibitor for 7B04 aluminum alloy in an aircraft fuel system

In this study, the broad-spectrum antimicrobial property of dodecyl dimethyl benzyl ammonium chloride (DDBAC) was investigated against three species of bacteria, Lysinibacillus sphaericus ( L. sphaericus ), Acinetobacter lwoffii ( A. lwoffii ), and Sediminibacterium salmoneum ( S. salmoneum ) isolated and purified from a naval aircraft fuel system. Through the inhibition zone method and minimum inhibitory concentration test, DDBAC was found to have a good antimicrobial performance with a minimum inhibitory concentration of 64 mg/L. The influence of DDBAC on the corrosion behavior of fuel tank material was evaluated by electrochemical measurements, such as polarization curve and electrochemical impedance spectroscopy (EIS). The polarization curve indicated that DDBAC suppressed anodic and cathodic reactions as a mixed-type corrosion inhibitor, and the inhibition efficiency was 68.38% at the concentration of 80 mg/L after 28 days of immersion. The EIS results showed that DDBAC inhibited the corrosion of 7B04 aluminum alloy in the concentration range of 40–120 mg/L. The DDBAC adsorption on the aluminum alloy surface was in agreement with the modified Langmuir adsorption isotherm model. The quantum chemical calculations proved that a lone pair of electrons of nitrogen atoms in DDBAC were able to form coordinate bonds with the empty orbital in aluminum, resulting in a tight chemisorption layer on the aluminum alloy surface and corrosion inhibition.

Antibacterial and Antifungal Activity of Functionalized Cotton Fabric with Nanocomposite Based on Silver Nanoparticles and Carboxymethyl Chitosan

Cotton is the most widely used natural fiber for textiles; however, the capacity of cotton fibers to absorb large amounts of moisture, retain oxygen, and have a high specific surface area makes them more prone to microbial contamination, becoming an appropriate medium for the growth of bacteria and fungi. In recent years, the incorporation of silver nanoparticles in textile products has been widely used due to their broad-spectrum antibacterial activity and low toxicity towards mammalian cells. The aim of the current study is to continue the assessment of our developed nanocomposite and evaluate the antibacterial and antifungal activity of the nanocomposite based on silver nanoparticles and carboxymethyl chitosan (AgNPs-CMC) against Escherichia coli, Staphylococcus aureus, and Candida albicans, evaluated by the well diffusion method. The antibacterial activity against E. coli and S. aureus was also evaluated by the qualitative method of inhibition zone and the quantitative method of colony counting. Likewise, the antifungal activity of the functionalized fabric against Candida albicans and Aspergillus niger was determined by the inhibition zone method and the antifungal activity method GBT 24346-2009, respectively. The functionalized fabric showed 100% antibacterial activity against E. coli and S. aureus and good antifungal activity against C. albicans and A. niger. Our results indicate that the functionalized fabric could be used in garments for hospital use to reduce nosocomial infections.

Fabrication of ZnO@Plant Polyphenols/Cellulose as Active Food Packaging and Its Enhanced Antibacterial Activity.

To investigate the efficient use of bioresources and bioproducts, plant polyphenol (PPL) was extracted from larch bark and further applied to prepare ZnO@PPL/Cel with cellulose to examine its potential as an active package material. The structure and morphology were fully characterized by XRD, SEM, FTIR, XPS and Raman spectra. It was found that PPL is able to cover ZnO and form a coating layer. In addition, PPL cross-links with cellulose and makes ZnO distribute evenly on the cellulose fibers. Coating with PPL creates a pinecone-like morphology in ZnO, which is constructed by subunits of 50 nm ZnO slices. The interactions among ZnO, PPL and cellulose have been attributed to hydrogen bonding, which plays an important role in guiding the formation of composites. The antibacterial properties against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) were tested by the inhibition zone method. Our composite ZnO@PPL/Cel has superior antibacterial activity compared to ZnO/Cel. The antibacterial mechanism has also been elaborated on. The low cost, simple preparation method and good performance of ZnO@PPL/Cel suggest the potential for it to be applied as active food packaging.

Impact of bandgap tuning on ZnS for degradation of environmental pollutants and disinfection.

The materials showing multiple applications are appealing for their practical use and industrial production. To realize the suitable property for various applications, we have produced ZnS (sf-ZnS) and metal-doped ZnS nanoflakes (sf-m-ZnS; where m = Cu, Ni, Cd, Bi, or Mn) and correlated their activity with bandgap variation. We obtained all these materials via hexamethyldisilazane (HMDS)-assisted synthetic method without using any surfactants, polymers, or template molecules and characterized them thoroughly using various techniques. Photocatalytic, as well as antibacterial, activities of these materials showed their bifunctional utility. We have demonstrated the effect of doping and consequent extension of absorption band to the visible region and resultant improved photocatalytic activity under sunlight. Thus, the change in bandgap influenced their performance as photocatalysts. Among all materials produced, sf-Cd-ZnS provided superior results as a photocatalyst while degrading two organic pollutants-rhodamine B (RhB) and methylene blue (MB) in water. The antibacterial activity of sf-ZnS and sf-m-ZnS against Gram-positive bacteria, i.e., Staphylococcus aureus (S. aureus), was examined by the zone of inhibition method, wherein sf-Ni-ZnS showed maximum activity. The enhanced activity of these ZnS materials can be attributed to the free surface of nanoparticles without any capping by organic molecules, which provided an intimate interaction of inorganic semiconductor material with organic and biomolecules. Thus, we have demonstrated modification of properties both by bandgap tuning of materials and providing the opportunity for intimate interaction of materials with substrates. The photocatalytic activity and antibacterial action of metal-doped ZnS produced by our method exhibited their potential for environmental remediation, specifically water purification.

Symbiotic bacteria on the cuticle protect the oriental fruit moth Grapholita molesta from fungal infection

The oriental fruit moth, Grapholita molesta (Lepidoptera: Tortricidae), is a destructive orchard pest native to the Asian subcontinent that has spread throughout many fruit-growing regions of the world. The entomopathogenic fungus Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae) is widely employed for control of insect pests, including G. molesta. Various studies have shown that microorganisms present on the insect cuticle can inhibit fungal spore germination and growth, thus inhibiting their pathogenicity and biological control efficacy. We conducted bioassays on larvae pre-treated with antibiotics to test whether cuticular microbiota could reduce the pathogenicity of B. bassiana to G. molesta. Control larvae (untreated with antibiotics) had higher survival than antibiotic-treated larvae following inoculation with B. bassiana, indicating that cuticular microbiota inhibited infection of G. molesta by B. bassiana. The bacterial diversity present on the cuticle of G. molesta larvae was characterized by 16S rDNA amplicon sequencing. The dominant bacterium isolated was Pantoea sp. and its antagonism toward B. bassiana was assayed in vitro using the inhibition zone method. Inhibitory effects on the pathogenicity of Pantoea sp. against B. bassiana were demonstrated by reintroducing the bacterium to G. molesta larvae that had been pre-treated with antibiotic, which increased their survival in comparison to antibiotic-treated larvae following inoculation with B. bassiana. This study provides potentially valuable insights for maximizing the efficacy of B. bassiana applications for biological control of G. molesta.

Chlorhexidine-grafted phenolamine coating to improve antibacterial property of the titanium surface

To investigate the physicochemical properties of pure titanium surface grafted with chlorhexidine (CHX) by phenolamine coating, and to evaluate its antibacterial activity and osteoblast-compatibility in vitro. Control group was obtained by alkali and thermal treatment, and then immersed in the mixture of epigallocatechin-3-gallate/hexamethylene diamine (coating group). Phenolamine coating was deposited on the surface, and then it was immersed in CHX solution to obtain the grafted surface of CHX (grafting group). The surface morphology was observed by scanning electron microscope, the surface element composition was analyzed by X-ray photoelectron spectroscopy, and the surface hydrophilicity was measured by water contact angle test. Live/dead bacterial staining, nephelometery, and inhibition zone method were executed to evaluate the antibacterial property. Cytotoxicity was evaluated by MTT assay and cell fluorescence staining. Bacteria-MC3T3-E1 cells co-culture was conducted to evaluate the cell viability on the samples under the circumstance with bacteria. Scanning electron microscope observation results showed that deposits of coating group and grafting group increased successively and gradually covered the porous structure. X-ray photoelectron spectroscopy results showed the peak of N1s enhanced and the peak of Cl2p appeared in grafting group. Water contact angle test results showed that the hydrophilic angle of three groups increased in turn, and there was significant difference between groups ( P<0.05). Live/dead bacteria staining results showed that the grafting group had the least amount of bacteria adhered to the surface and the proportion of dead bacteria was high. The grafting group had a transparent inhibition zone around it and the absorbance ( A) value did not increase, showing significant difference when compared with control group and coating group ( P<0.05). MTT assay and cell fluorescence staining results showed that the number of adherent cells on the surface of the grafting group was the least, but the adherent cells had good proliferation activity. Bacteria-cell co-culture results showed that there was no bacteria on the surface of grafting group but live cells adhered well. CHX-grafted phenolamine coating has the ability to inhibit bacterial adhesion and proliferation, and effectively protect cell adhesion and proliferation in a bacterial environment.

In Vitro Study of Synergistic Activities of Phyllanthus emblica L. Leaves and Garcinia mangostana L. Peels Crude Extracts to Cutibacterium acnes

Background: Due to the increasing antibiotic resistant Cutibacterium acnes, studies have substantiated the effectiveness of botanical extracts to inhibit C. acnes. Both Phyllanthus emblica L. leaves and Garcinia mangostana L. peels have good efficacy in inhibiting C. acnes growth. However, the combination of both herbal extracts on antimicrobial synergistic activities has not been studied. Objective: To perform an in vitro study of synergistic activities of Phyllanthus emblica L. leaves and Garcinia mangostana L. peels crude extracts to C. acnes. Materials and Methods: The present report was an experimental, cross-sectional study. Seventy isolates of C. acnes from clinical isolations were tested with each crude extract by agar well diffusion method to evaluate minimum inhibition zone (MIZ) and broth microdilution method to evaluate minimum inhibitory concentration (MIC). Thirty-five isolates of C. acnes were tested with the combination of both extracts by antimicrobial synergy study-checkerboard testing to evaluate fractional inhibitory concentration (FIC). Results: The medians (Q1, Q3) MIZ of P. emblica and G. mangostana at 5 mg/mL were 15.75 (12.00, 18.50), and 10.00 (10.00, 15.00) mm, respectively, with significant difference (p&lt;0.001). The medians (Q1, Q3) MIC of P. emblica and G. mangostana were 0.078 (0.039, 0.156), and 0.078 (0.078, 0.078) mg/mL, respectively, without significant difference (p=0.327). The checkerboard testing showed FIC indices of 0.192 to 3.333. The synergy activity was 62.86% of the synergy group, 37.14% of the non-synergy group, and none of antagonism, without significant difference between resistant C. acnes and susceptible C. acnes (p=0.708). Conclusion: Both P. emblica leaves and G. mangostana peels crude extracts could inhibit resistant and susceptible C. acnes. The combination of both herbal extracts increases antimicrobial synergistic activity, suggesting a utilization of these herbs in combination therapy against antibioticresistant C. acnes. Keywords: Phyllanthus emblica L.; Garcinia mangostana L.; Antimicrobial synergistic activity; Cutibacterium acnes; Crude extract

Preparation and evaluation of antibacterial wound dressing based on vancomycin-loaded silk/dialdehyde starch nanoparticles.

One of the main reasons infected wounds go untreated is that antibiotic-resistant bacteria mainly cause infection. Vancomycin is an antibiotic used against Gram-positive bacteria, such as MRSA, but it has limited intravenous use due to its toxicity. This study describes using a local drug delivery approach at the wound site. The aim is to prepare a silk dressing containing dialdehyde starch nanoparticles loaded with vancomycin that can cure infection through the controlled release of antibiotics. First, the starch was oxidized by sodium periodate solution and converted to dialdehyde starch. Dialdehyde starch was converted into nanoparticles by the microemulsion method. Simultaneously, with nanoparticle formation, the antibiotic vancomycin (VAN), added to the solution, was loaded into the dialdehyde starch nanoparticles (DASNP). The wound dressing (SF/DASNP/VAN) was prepared by adding nanoparticles containing antibiotics to the silk fibroin (SF) solution, and then, the solution containing the nanoparticles was freeze-dried, and the nanoparticles were placed inside the silk matrix. Drug release of dressings was performed by immersion in phosphate-buffered saline, and cytotoxicity by MTT assay and antibacterial properties of dressings were investigated by the inhibition zone method. The morphology of the SF/DASNP/VAN dressing, its biocompatibility, antibacterial efficiency, and antibiotic release kinetics were assessed. The synthesized dressing has the desired biocompatibility with 69% cell viability and shows antibacterial properties against MRSA with a growth inhibition zone diameter of 12mm. Also, VAN was successfully incorporated into the dressing, resulting in a 144-h continuous release profile. It may be concluded that the fabricated dressing based on silk and dialdehyde starch nanoparticles opens up a new option for topical administration of antibiotics. We believe its properties can be considered a new dressing for infectious wounds by reducing infection associated with controlled drug delivery.