Bacterial Survival Rate Research Articles

IL-27 mediates immune response of pneumococcal vaccine SPY1 through Th17 and memory CD4+T cells

Vaccination is an effective means of preventing pneumococcal disease and SPY1 is a live attenuated pneumococcal vaccine we obtained earlier. We found IL-27 and its specific receptor (WSX-1) were increased in SPY1 vaccinated mice. Bacterial clearance and survival rates were decreased in SPY1 vaccinated IL-27Rα-/- mice. The vaccine-induced Th17 cell response and IgA secretion were also suppressed in IL-27Rα-/- mice. STAT3 and NF-κB signaling and expression of the Th17 cell polarization-related cytokines were also decreased in IL-27Rα-/- bone-marrow-derived dendritic cells(BMDC) stimulated with inactivated SPY1. The numbers of memory CD4+T cells were also decreased in SPY1 vaccinated IL-27Rα-/- mice. These results suggested that IL-27 plays a protective role in SPY1 vaccine by promoting Th17 polarization through STAT3 and NF-κB signaling pathways and memory CD4+T cells production in the SPY1 vaccine. In addition, we found that the immune protection of SPY1 vaccine was independent of aerobic glycolysis.

Osteogenic and antibacterial PLLA membrane for bone tissue engineering

Insufficient bone regeneration and bacterial infection are two major concerns of bone repair materials. Poly-L-lactic acid (PLLA) have been widely used in bone tissue engineering (BTE), however, lack of osteogenic and antibacterial properties have greatly limit its clinical application. Herein, PLLA membrane was firstly treated with polydopamine (PDA), and then modified with ε-polylysine (ε-PL) and alginate (ALG) via layer-by-layer method. The (ε-PL/ALG)n composite layer coated PLLA (PLLA@(ε-PL/ALG)n) could facilitates the adhesion and osteoblast differentiation of MC3T3-E1 cells. Furthermore, PLLA@(ε-PL/ALG)n presents an effective antibacterial efficacy against S. aureus and E. coli, and the bacterial survival rates of S. aureus and E. coli on PLLA@(ε-PL/ALG)10 were 21.5 ± 3.5 % and 13 ± 2.1 %, respectively. This work provides a promising method to design PLLA materials with osteogenic and antibacterial activity simultaneously. Furthermore, the method is also an optional choice to construct multifunctional coatings on the other substrate.

Effect of prebiotic supplementation on the low-temperature storage stability and in vitro gastrointestinal tolerance of Bifidobacterium breve and Bifidobacterium longum in lactose and sucrose systems

The objective of this study was to investigate the effect of fructooligosaccharides (FOS) and inulin supplementation on the stability of Bifidobacterium breve and Bifidobacterium longum grown in lactose and sucrose systems over 12-week low-temperature storage at 4 °C. FOS and inulin supplementation in the lactose and sucrose systems improved the low-temperature storage stability of B. breve and B. longum. On week 12, the highest lactic (29.7 ± 0.7%) and acetic acid (28.7 ± 1.3%) concentrations were observed in B. breve in 2% lactose with 3% inulin supplementation. In week 12, B. breve auto-aggregation rate and hydrophobicity significantly increased in 2% lactose with 3% inulin supplementation than non-supplemented (2% lactose). At week 0, the co-aggregation of B. longum and B. breve with E. faecalis and E. coli significantly increased compared to non-supplemented media. However, as the storage week proceeded, the co-aggregation ability of B. longum and B. breve drastically declined. FOS and inulin supplementation in these sugar systems significantly improved hydrophobicity, auto-aggregation, and co-aggregation ability with Enterococcus faecalis and Escherichia coli compared to non-supplemented media. In addition, the increase in the bacterial survival rate in vitro gastrointestinal tolerance assay showed that FOS and inulin supplementation in these sugar systems improved the gastric-intestinal tolerance of B. breve and B. longum.

Application of expanded perlite immobilized microorganisms in cementitious materials

Cementitious materials are the most widely used building materials worldwide, and microbially induced calcium carbonate deposition technology makes them self-diagnostic and self-healing. However, the direct incorporation of active microorganisms leads to interaction between microorganisms and cement matrix, which seriously affects the bacterial survival rate as well as the performance of the cement matrix itself. This paper first investigates the different components of the microorganisms and shows that the nutrients and metabolites of the microorganisms adversely affect the setting time, flow and compressive strength of the cementitious material. The adsorption and protective effects of expanded perlite on microorganisms were verified by introducing expanded perlite as a carrier. The mechanical properties of the specimens and the survival of the microorganisms were investigated in different modes by immobilizing the microorganisms and adding them to the cementitious material. The surface healing rate, the recovery rate of compressive and flexural strength, and the relative permeability coefficient of cracks were used to evaluate and compare the crack healing of cementitious materials by microorganisms in different immobilized modes. The results showed that the use of microbial spores immobilized in expanded perlite led to a higher density of microorganisms in the specimens of 8.6 × 104 cfu/g, and the maximum healing width of cracks increased by 55.9% to 0.71 mm compared with the carrier-free group, and the average healing rate of cracks could reach 90.2% when the crack width was less than 0.6 mm. When subjected to 60% pre-pressure, the recovery rates of compressive and flexural strengths could reach 95.32% and 102.4% meanwhile, the relative permeability coefficient of the specimens also decreased by 81.3% to 0.076 after maintenance.

Construction of Probiotic Double-Layered Multinucleated Microcapsules Based on Sulfhydryl-Modified Carboxymethyl Cellulose Sodium for Increased Intestinal Adhesion of Probiotics and Therapy for Intestinal Inflammation Induced by Escherichia coli O157:H7.

The decreased number of viable bacteria and the ability of Bifidobacterium to adhere to and colonize the gut in the gastrointestinal environment greatly limit their efficacy. To solve this problem, thiolated carboxymethyl cellulose sodium (CMC) probiotic double-layered multinucleated microcapsules with Bifidobacterium adolescentis FS2-3 in the inner layer and Bacillus subtilis SN15-2 embedded in the outer layers were designed. First, the viable counts and release rates of microcapsules were examined by in vitro simulated digestion assays, and it was found that microcapsules were better protected from gastrointestinal digestion than the controls. Compared with free Bifidobacterium strains, double-layered multinucleated microcapsules have higher viable bacterial survival rates and storage stability. Second, through in vitro rheology, tensile tests, isotherm titration calorimetry, and adhesion tests, it was observed that thiolated CMC could enhance the strong interaction of Bifidobacterium with intestinal mucus and significantly promote the proliferation and growth of probiotics. Finally, double-layered multinucleated microcapsules containing B. adolescentis FS2-3 and B. subtilis SN15-2 modified with sulfhydryl-modified CMC were studied in the intestine. Alleviation of Escherichia coli O157:H7 induced intestinal inflammation. The results showed that microencapsulation could significantly increase the colon content of Bifidobacterium, relieve intestinal inflammation symptoms in mice with bacterial enteritis, and repair the intestinal microbiota disorder caused by inflammation. The probiotic double-layered multinucleated microcapsules prepared in this study can improve the survival rate of probiotics and promote proliferation, adhesion, and colonization of probiotics.

Antibacterial properties of antimicrobial peptide HHC36 modified polyetheretherketone.

Polyetheretherketone (PEEK) is considered to be a new type of orthopedic implant material due to its mechanical properties and biocompatibility. It is becoming a replacement for titanium (Ti) due to its near-human-cortical transmission and modulus of elasticity. However, its clinical application is limited because of its biological inertia and susceptibility to bacterial infection during implantation. To solve this problem, there is an urgent need to improve the antibacterial properties of PEEK implants. In this work, we fixed antimicrobial peptide HHC36 on the 3D porous structure of sulfonated PEEK (SPEEK) by a simple solvent evaporation method (HSPEEK), and carried out characterization tests. We evaluated the antibacterial properties and cytocompatibility of the samples in vitro. In addition, we evaluated the anti-infection property and biocompatibility of the samples in vivo by establishing a rat subcutaneous infection model. The characterization test results showed that HHC36 was successfully fixed on the surface of SPEEK and released slowly for 10 days. The results of antibacterial experiments in vitro showed that HSPEEK could reduce the survival rate of free bacteria, inhibit the growth of bacteria around the sample, and inhibit the formation of biofilm on the sample surface. The cytocompatibility test in vitro showed that the sample had no significant effect on the proliferation and viability of L929 cells and had no hemolytic activity on rabbit erythrocytes. In vivo experiments, HSPEEK can significantly reduce the bacterial survival rate on the sample surface and the inflammatory reaction in the soft tissue around the sample. We successfully loaded HHC36 onto the surface of SPEEK through a simple solvent evaporation method. The sample has excellent antibacterial properties and good cell compatibility, which can significantly reduce the bacterial survival rate and inflammatory reaction in vivo. The above results indicated that we successfully improved the antibacterial property of PEEK by a simple modification strategy, making it a promising material for anti-infection orthopedic implants.

The Effect of Decreased Ca++/Mg++ ATPase Activity on Lactobacillus delbrueckii subsp. bulgaricus sp1.1 Survival during Spray Drying.

Compared with the commonly used technique of freeze-drying, spray drying has lower energy costs. However, spray drying also has a fatal disadvantage: a lower survival rate. In this study, the survival of bacteria in a spray-drying tower decreased as the water content was reduced. The water content of 21.10% was the critical point for spray drying Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) sp1.1 based on sampling in the tower. Based on the relationship between the moisture content of spray drying and the survival rate, the water content of 21.10% was also the critical point for the change in the survival rate during spray drying. Proteomic analysis was used to investigate the reasons for L. bulgaricus sp1.1 inactivation during and after spray drying. Gene Ontology (GO) enrichment revealed that differentially expressed proteins were mainly associated with the cell membrane and transport. In particular, proteins related to metal ion transport included those involved in the transport of potassium, calcium and magnesium ions. The protein-protein interaction (PPI) network revealed that Ca++/Mg++ adenosine triphosphatase (ATPase) may be a key protein. Ca++/Mg++ ATPase activity decreased substantially during spray drying (p < 0.05). Supplementation with Ca++ and Mg++ significantly increased the expression of ATPase-related genes and enzyme activity (p < 0.05). The Ca++/Mg++ ATPase activity of L. bulgaricus sp1.1 was enhanced by increasing the intracellular Ca++ or Mg++ concentration, thus increasing the survival of spray-dried LAB. Bacterial survival rates were increased to 43.06% with the addition of Ca++ and to 42.64% with the addition of Mg++, respectively. Ca++/Mg++ ATPase may be the key to the damage observed in spray-dried bacteria. Furthermore, the addition of Ca++ or Mg++ also reduced bacterial injury during spray drying by enhancing the activity of Ca++/Mg++ ATPase.

Gold − Titanium dioxide heterojunction for enhanced sonodynamic mediated biofilm eradication and peri-implant infection treatment

Peri-implant infection caused by bacterial biofilm is the main reason for dental implant repair failure. The success of controlling infection depends mainly on eliminating bacterial biofilm. However, traditional medicine therapy is not practical due to the growth of bacterial resistance. Recently, antibacterial sonodynamic therapy (aSDT) activated by ultrasound has been recognized as an emerging strategy for treating biofilm infections. In this study, an activatable nanoplatform (Au-TNT) fabricated on the implant surface is proposed for aSDT. Au-TNT could rapidly produce O2 under ultrasonic irradiation, which could relieve the hypoxic microenvironment of biofilm and improve the anti-biofilm efficiency of aSDT. Furthermore, it could generate singlet oxygen (1O2) and hydroxyl radicals (OH), resulting in a powerfully high antibacterial capacity for both single and multi-species pathogenic biofilms as assessed by bacterial survival rate, cell membrane rupture, biofilm metabolism and thickness. Meanwhile, Au-TNT exhibited excellent antibacterial ability in vivo with a 3 logs CFU decreased compared to the control group. Interestingly, it also showed that Au-TNT downregulated inflammatory factor levels and promoted bone repair. Thus, this study provides a sonodynamic-catalytic nanoplatform for efficient biofilm eradication and peri-implant infection treatment.

Z-Scheme CuOx/Ag/TiO2 Heterojunction as Promising Photoinduced Anticorrosion and Antifouling Integrated Coating in Seawater.

In the marine environment, steel materials usually encounter serious problems with chemical or electrochemical corrosion and fouling by proteins, bacteria, and other marine organisms. In this work, a green bifunctional Z-scheme CuOx/Ag/P25 heterostructure coating material was designed to achieve the coordination of corrosion prevention and antifouling by matching the redox potential of the reactive oxygen species and the corrosion potential of 304SS. When CuOx/Ag/P25 heterostructure was coupled with the protected metal, the open circuit potential under illumination negatively shifted about 240 mV (vs. Ag/AgCl) and the photoinduced current density reached 16.6 μA cm-2. At the same time, more reactive oxygen species were produced by the Z-shape structure, and then the photocatalytic sterilization effect was stronger. Combined with the chemical sterilization of Ag and the oxide of Cu, the bacterial survival rate of CuOx/Ag/P25 was low (0.006%) compared with the blank sample. This design provides a strategy for developing green dual-functional coating materials with photoelectrochemical anticorrosion and antifouling properties.

Neutrophil membrane-coated nanoparticles exhibit increased antimicrobial activities in an anti-microbial resistant K. pneumonia infection model

ObjectiveTo investigate the efficacy and safety of neutrophil membrane-coated nanoparticles mediated KLA peptides (KLAKLAKKLAKLAK) and gentamicin in the targeted therapy of anti-microbial resistant Klebsiella pneumoniae (K. pneumonia) lung infection. MethodsThe characteristics of KLA-neutrophils nanoparticles (NNPs) are identified via dynamic light scattering (DLS), transmission electron microscope (TEM), SDS-PAGE, Western blot, quantitative flow cytometry (QFCM) and confocal microscopy. The safety of KLA-NNPs both in vitro and in vivo is evaluated by hemolysis test, platelet α granule membrane protein concentration, protein adsorption capacity, in vitro macrophage phagocytosis, weight change, liver function indicators, blood biochemical indicators, and pathological changes of vital organs in mice. The efficacy of KLA-NNPs is determined by time-kill assay, fluorescent label test, intracellular bacterial content, caspase-1 activity, survival rate, and HE staining both in vitro and in vivo. ResultsThe prepared KLA-NNPs have a typical “core-shell” structure, uniform nanometer size, and retain the membrane proteins on the neutrophil membrane that achieve functional effects. In vitro safety analysis showed that KLA-NNPs have good blood compatibility and can inhibit macrophage phagocytosis in vitro. KLA-NNPs can effectively release KLA and significantly reduce intracellular bacteria and caspase-1 activity. In vivo safety analysis and efficacy analysis revealed that KLA-NNPs have good biocompatibility and could effectively improve the survival rate of mice. ConclusionThe prepared KLA-NNPs have good nano-medicine chemical and physical properties and safety. It can evade immune system clearance, achieve high-efficiency targeted aggregation and drug delivery to bacterial infection sites, and effectively inhibit the development of pneumonia induced by drug-resistant K. pneumonia.

Development and Characterization of Novel Orthodontic Adhesive Containing PCL-Gelatin-AgNPs Fibers.

Enamel demineralization around brackets is a relatively common complication of fixed orthodontic treatment, which seriously affects the aesthetics of teeth. In this study, a novel orthodontic adhesive containing polycaprolactone−gelatin−silver nanoparticles (PCL−gelatin−AgNPs) composite fibers was prepared to prevent enamel demineralization of orthodontic treatment. First, PCL−gelatin−AgNPs fibers film prepared by electrospinning was made into short fibers and added to traditional orthodontic adhesives (Transbond XT, 3M Unitek) in three different ratios to design a series of composite adhesives containing antibacterial materials. The antimicrobial performance of the control product and the three samples were then evaluated by bacterial live/dead staining, colony-forming unit (CFU) counts, tensile bond strength (TBS), and adhesive residue index (ARI) scores. The composite adhesives’ antimicrobial properties increased with the increasing content of PCL−gelatin−AgNPs short fibers. The addition of complex antimicrobial fibers to 3M Transbond XT adhesive can significantly reduce the CFU of bacterial biofilms (p < 0.05). The bacterial survival rate on the surface of the specimen decreased with the increase of PCL−gelatin−AgNPs short fibers (p < 0.05). The TBS and ARI values (n = 10) indicated that adding PCL−gelatin−AgNPs short fibers had no significant adverse effect on adhesion. Therefore, adding PCL−gelatin−AgNPs short fibers makes it possible to fabricate orthodontic adhesives with strong antibacterial properties without compromising the bonding ability, which is essential for preventing enamel demineralization around the brackets.

Application of Biomineralization Technology to Self-Healing of Fiber-Reinforced Lightweight Concrete after Exposure to High Temperatures.

In the field of civil engineering, concrete self-healing technology plays an important role. Concrete self-healing should be able to effectively heal cracks, not only improving the internal structure, but also improving the mechanical properties and durability of the concrete structure. The biomineralization-repair method is characterized by its potential for long-lasting, rapid, and active crack repair potential. Biomineralization repair has an effective bond ability, is compatible with concrete components, and is also environmentally friendly. This study used biomineralization to explore the self-healing of fiber-reinforced lightweight concrete after its exposure to high temperatures. Concrete specimens of a control group (using lightweight aggregate without bacterial spores and a nutrient source) and an experimental group (using lightweight aggregate containing bacterial spores and a nutrient source) were prepared. The repair effect of the microbial self-healing concrete after the exposure to high temperature was observed by a crack-width gauge, field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). According to the EDS and XRD analyses, the precipitate formed at the crack was calcium carbonate. After 28 days of self-healing, the water absorption rate of the experimental group was lower than that of the control group. This is because the specimens of the penetration test were taken from the middle of the concrete cylinder after high temperature, and their bacterial survival rate was higher, which made the mineralization more significant. However, the mechanical test results of the control and experimental groups after the self-healing in the water were not substantially different, which indicated that the bacterial mineralization in the experimental group was slow in the absence of an adequate source of nutrients.

Antioxidant and antibacterial PBAT/lignin-ZnO nanocomposite films for active food packaging

In present works, the lignin-zinc oxide (LZn) hybrid particles composed with lignin nanoparticles (LNP) and zinc oxide (ZnO) were prepared by a simple hydrothermal method under different pH conditions. Results from infrared spectra, thermogravimetric analysis, and elemental analysis evidenced the successful synthesis of LZn hybrids. The bacterial survival rate of LZn-9 (pH=9) against E. coli and S. aureus decreased to 9% and 49%, while the value of LNP was 69% and 80%, respectively. Then glyceryl methacrylate (GMA) was grafted on poly (butyleneadipate-co-terephthalate) (PBAT), following by the addition of LZn hybrid to prepare the master batches. Finally, the master batches were catalyzed by trimethylamine, and the PBAT-G-xLZn composite films were produced. The tensile modulus and yield strength of PBAT-G-3LZn increased by 35.2% and 28.6% compare with pure PBAT, respectively. The PBAT/LZn composite films were found to have obvious UV shielding, antioxidant and antibacterial activities. Composites belong to the contact type antibacterial, the bacterial adhesion rates of PBAT-G-xLZn were obviously reduced compare with pure PBAT. The transmittance at λ = 320 nm of PBAT-G-3LZn film was only 0.16%, and the radical scavenging activity (RSA) value was 11.6%. The Zn2+ migration concentration of PBAT-G-3LZn was only 3.3 μg/L. Therefore, the PBAT/LZn composite films were believed to be applied for active food packaging.

Investigation of bactericidal effect of a mid-infrared free electron laser on Escherichia coli

The rapid increase in the number of bacteria that are resistant to many commonly used antimicrobial agents and their global spread have become a major problem worldwide. In particular, for periodontal disease, which is a localized infection, there is a growing need for treatment methods that do not primarily involve antimicrobial agents, and antimicrobial photodynamic therapy (aPDT) is attracting attention. In this study, the bactericidal effects of a mid-infrared free electron laser (MIR-FEL) on E. coli were investigated as a basic study to examine the applicability of MIR-FELs, which can selectively excite molecular vibrations due to their wavelength tunability, to aPDT. The optimal irradiation wavelengths to be examined in this study were determined from the infrared spectrum of the bacteria, which was obtained using Fourier transform infrared spectroscopy. Five irradiation wavelengths (6.62, 6.88, 7.14, 8.09 and 9.26 µm) were selected from the FT-IR spectrum, and we found that the bactericidal effects at a wavelength of 6.62 µm were markedly stronger than those observed at the other wavelengths. At this wavelength corresponding to the Amide II band, the bacterial survival rate decreased significantly as the irradiation time increased. On the contrary, irradiation of a neodymium-doped yttrium aluminum garnet (Nd: YAG) laser at 1.06 µm exhibited no distinct bactericidal effect. No morphological changes were observed after MIR-FEL irradiation, suggesting that a bacterial organelle molecule may be the target of MIR-FEL irradiation, but the exact target was not identified. Furthermore, the temperature change induced in the culture medium by the laser irradiation was ± 1.5 °C at room temperature. These results suggest that the bactericidal effects of MIR-FEL are derived from photochemical reactions involving infrared photons, since E. coli is usually killed by heating it to 75 °C for 1 min or longer.

Fabrication of a Highly Efficient Wood-Based Solar Interfacial Evaporator with Self-Desalting and Sterilization Performance.

Solar interfacial evaporation based on wood-derived materials has been considered a promising strategy for desalination and wastewater purification. Herein, we adopted delignified wood (DW) as the water transport substrate and lignosulfonate (LS)-modified narrow-band gap semiconductor nickel disulfide (NiS2) as the light-absorbing agent (LS-NiS2) to fabricate a high-efficiency evaporator (LS-NiS2@DW). On the one hand, the high absorbance (>95%) within a broad wavelength range and excellent photothermal conversion efficiency of LS-NiS2 endow efficient solar energy utilization. On the other hand, the hydrophilicity of DW facilitates water activation, which results in a lower evaporation enthalpy of LS-NiS2@DW (1274.4 kJ kg-1) than that of pure water. By combining LS-NiS2 and DW, LS-NiS2@DW achieved an evaporation rate as high as 2.80 kg m-2 h-1 under one sun irradiation (1 kW m-2), and the evaporation efficiency reached 87.4%. Notably, LS-NiS2@DW exhibits a high evaporation rate (2.42-2.69 kg m-2 h-1) in simulated seawater for 24 h with no salt crystals formed on the surface. Moreover, LS-NiS2@DW shows high antibacterial activity with about 90% reduction in bacterial survival rate. This work could provide new perspectives for the design of a high-efficiency wood-based photothermal evaporator.

Formulation of chewing gum containing Lactobacillus brevis NB10

Lactobacillus brevis NB10 isolated from human saliva, showed in vitro effect on inhibiting the growth and the biofilm formation of Streptococcus mutans - a major pathogen that initiates dental plaque and caries. Formulation of chewing gum containing L. brevis NB10 is the next step in using this probiotic for the prevention of dental diseases related to S. mutans. Cryoprotectants such as sorbitol, mannitol, xylitol, lactose, maltodextrin, skim milk and potassium ascorbate were selected to formulate the freeze-dried powder containing L. brevis NB10. Next, the freeze-dried powder of L. brevis NB10 was used to make chewing gum by direct compression method using HIG-04 gum base (Heath in Gum ®). Other ingredients such as xylitol, strawberry flavor powder, glycerin, aerosil, talc, and magnesium stearate were selected to formulate chewing gum with suitable chewing feel, taste, and flavor. The freeze-dried powder showing the highest bacterial survival rate (75.5 ± 7.6%) consists of 6% maltodextrin, 6% skim milk, and 0.25% potassium ascorbate. The optimal formula of chewing gum tablet consists of 10% L. brevis NB10 freeze-dried powder, 10% xylitol, 2% strawberry powder, 1.5% glycerol, 1.5% magnesium stearate, 1.5% talc and 2.5% aerosil. The bacterial survival rate after tablet compression is 34.34 ± 0.55 %. The product is stable for at least 3 months at 5 °C ± 3 °C. This study was successful in formulating chewing gum containing at least 107 CFU/tablet of L. brevis NB10.

Experimental evolution of bacterial survival on metallic copper

AbstractAntimicrobial copper‐containing surface materials have a great potential of reducing the risks of healthcare‐associated infections (HAIs), but their increased use in hospital facilities may select copper‐resistant strains, causing concerns to antimicrobial resistance management. Here, we describe a long‐term bacterial evolution experiment wherein a non‐pathogenic Pseudomonas strain was subjected to daily transfer in laboratory media with and without copper‐mediated contact killing. The copper treatment sequentially involved two surface materials differing in Cu content and thus contact killing effectiveness: first on brass (Cu 63.5%) and then on pure copper (Cu 99.9%). A gradual increase in bacterial survival rate (or a decrease of killing effectiveness) was observed over time on the related copper surfaces. For the final evolved populations after 320 transfers, 37.8% cells of the copper‐evolved populations were able to survive 60 min on pure copper, whereas populations in the control lines remained sensitive with a survival rate of 0.09% under the same contact killing condition. Genome re‐sequencing revealed ~540 mutations accumulated in the copper lines but only 71, on average, in the control lines (variant frequency &gt; 0.5). The mutagenic activities of Cu+ ions were confirmed by measuring spontaneous mutation rate in a laboratory medium supplemented with copper sulfate at a non‐inhibitory concentration. The copper‐evolved populations have acquired increased resistance to Cu+ ions and tobramycin (an aminoglycoside antibiotic), but showed decreased production of biofilm, exoprotein, and pyoverdine. Together, our data demonstrate the potential of bacteria to evolve prolonged survival on metallic copper, and the long‐term impacts should be considered with increased copper usage in hospital environments.

Optimization of fermentation medium for biocontrol strain Pantoea jilinensis D25 and preparation of its microcapsules

A newly isolated biocontrol strain, Pantoea jilinensis D25, can effectively inhibit Botrytis cinerea caused tomato gray mold. However, the short shelf-life limits its biopesticide applications. This study optimized the fermentation medium for P. jilinensis D25. Also, the best microencapsulation conditions were determined. P. jilinensis D25 microcapsules (D25Ms) were evaluated for storage stability and biofilm formation ability. The results showed that the optimal medium composition contained sucrose (19.65 g/L), tryptone (2.73 g/L), NaCl (20.71 g/L), and yeast extract (13.00 g/L) at pH 6–8. The optimal fermentation conditions were temperature 25 ℃, inoculation amount 2 %, rotation speed 150 r/min, and liquid volume 75 mL. Maltodextrin was found to be an effective microencapsulation wall material showing a great protective effect on P. jilinensis D25. The bacterial survival rate was the highest (90.83 %) for conditions: maltodextrin 80 %, air-inlet temperature 130 ℃, feed flow rate 500 mL/h, and spray pressure 0.15 MPa. D25Ms were stored at 4 ℃ for 180 days showing the bacterial survival rates of 95.1 %. Compared with free cells, the biofilm formation ability of D25Ms was 1.86 times higher. Overall, D25Ms with good stability and biofilm formation ability can be a potential biocontrol agent.

Diatomite and Na-X zeolite as carriers for bacteria in self-healing cementitious mortars

The use of bacteria in the self-healing process of cementitious composites has been recently widely considered. In this study, diatomite and the Na-X zeolite were proposed as carrier materials impregnated by the Bacillus subtilis endospores. The effect of the impregnation method on a bacterial survival rate (BSR) and cement composites modification method on the strength parameters, was investigated. Additionally, the influence of modification and healing method on the flexural and compressive strength recovery and surface crack repair ratio, was assessed. Test results indicated higher BSR for a vacuum impregnated than immersed samples (up to 31% after 28 days of storage for the impregnated Na-X zeolite). The BSR in the self-healing mortar may be promoted by local pH reduction in the vicinity of carrier particles, especially diatomite (pHPZC = 4.6). Mortars containing medium dissolved in the mixing water showed an increase in the flexural and compressive strength (up to 10.4% and 18.0%, respectively). The addition of bacteria immobilized on the both carrier materials caused a decrease of strength properties (to 16.6%), while the series containing both bacteria and the medium attained the strength properties similar or better than the reference series and the series with carrier materials alone. Series containing bacteria immobilized on carrier material and with medium showed a self-healing ability, which was confirmed by the compressive strength recovery and surface repair ratio of 32.6% and 92.6%, respectively. The increased precipitation of CaCO3 was confirmed by the SEM and EDS analysis.

Optimization of antibacterial activity of new poly(vinyl alcohol)–gum arabic–MgO nanoparticles bionanocomposite

Untreated dental caries is an important challenge in human life. In this work, the authors synthesized a new poly(vinyl alcohol) (PVA)–gum arabic (GA)–magnesium oxide (MgO) nanoparticle bionanocomposite and evaluated its antibacterial properties against Streptococcus mutans biofilm in vitro. For optimization of variables to obtain the maximum antibacterial properties, the L9 orthogonal array of the Taguchi method was used for the design of extraction conditions. The nanocomposites were characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy, thermogravimetric analysis and transmission electron microscopy. The FESEM images of the nanocomposite show that the nanoparticles are entirely surrounded with polymer chains of the matrix and nanoparticles are deposited on its walls; thus, a layered nanocomposite is formed. The sheet width and size ranges of the nanocomposite were determined to be between 30 and 40 and 20 and 90 nm, respectively. The results showed that the nanocomposite synthesized under conditions of 1 mg/ml PVA, 3 mg/ml GA and 6 mg/ml magnesium oxide (experiment 3) had the strongest antibacterial activity against the S. mutans bacteria’s biofilm. Under these optimal conditions, the bacterial survival rate was the lowest at 0.21 colony-forming units (CFU)/ml and the activity of S. mutans bacteria could be inhibited at a rate of 0.09 CFU/ml.