Bacterial Suspension Research Articles

In vitro Antibacterial Effect Study of Plasma-Activated Saline on Mycobacterium Tuberculosis.

This study aimed to investigate the antibacterial effects of plasma-activated saline (PAS) on My-cobacterium tuberculosis (Mtb). We conducted a growth assay on 3 strains of Mtb and an antibiotic sensitivity test on 4 strains of Mtb. Both tests included groups treated with normal saline (NS), PAS, and hydrochloric acid (HCl). The test of antibiotic sensitivity consisted of parallel tests with two concentrations of bacteria suspension: 10-2 and 10-4. The selected antibiotics were rifampicin (RIF), isoniazid (INH), ethambutol (EMB), and streptomycin (SM). The number of bacteria was determined after one month of culture under different conditions. The Kruskal-Wallis test was used to analyze the differences in grouping factors at representative time points. The growth assay indicated that PAS significantly inhibited the growth of 3 strains of Mtb compared with NS and HCl treatment groups. Furthermore, except for the initial observation time point, the remaining three observation time points consistently demonstrate no significant differences between the NS group and the HCl group. The antibiotic sensitivity test of INH, SM, and RIF indicated that PAS could inhibit the growth of antibiotic-resistant Mtb, and the antibiotic sensitivity test of INH and SM with bacterial suspension concentration of 10-2 and SM with bacterial suspension concentration of 10-4 showed statistically different results. The antibiotic sensitivity test of EMB indicated that the growth of Mtb in PAS was slower than that in NS and HCl in both antibiotic-resistant and sensitive Mtb, but there was no statistical difference. The study indicates that PAS contains a significant amount of active substances and exhibits high oxidizability and an acidic pH state. The unique physicochemical properties of PAS significantly delayed the growth of Mtb, compared to the NS and the HCl. PAS not only inhibited the growth of drug-sensitive strains but also significantly enhanced the sensitivity of drug-resistant strains to anti-tuberculosis drugs, which may provide a new therapeutic strategy for the treatment of tuberculosis.

Negative Pressure Level and Effects on Bacterial Growth Kinetics in an in vitro Wound Model.

Negative Pressure Wound Therapy (NPWT) has been widely adopted in wound healing strategies due to its multimodal mechanism of action. While NPWT's positive impression on wound healing is well-established, its effect on bacterial load reduction remains equivocal. This study investigates NPWT's efficacy in reducing bioburden using an in vitro porcine skin model, focusing on the impact of Staphylococcus aureus and Staphylococcus epidermidis. Custom-made negative pressure chambers were employed to apply varying negative pressures. Porcine skin was cut into 5 × 5 cm squares and three standardized wounds of 6 mm each were created using a biopsy punch. Then, wounds were infected with S. aureus and S. epidermidis bacterial suspensions diluted 1:10,000 to obtain a final concentration of 1.5 × 104 CFU/ml and were placed in negative pressure chambers. After incubation, bacterial counts were expressed as colony-forming units (CFU) per ml. For S. aureus at 120 hours, the median CFU, mean area per colony, and total growth area were notably lower at -80 mmHg when compared to -250 mmHg and -50 mmHg, suggesting an optimal negative pressure for the pressure-dependent inhibition of the bacterial proliferation. While analyzing S. epidermidis at 120 hours, the response to the negative pressure was similar but less clear, with the minor CFU at -100 mmHg. The influence of intermittent negative pressure on the S. epidermidis growth showed notably lower median CFU with the interval therapy every hour compared to the S. aureus control group. This study contributes valuable insights into NPWT's influence on the bacterial load, emphasizing the need for further research to reformulate its role in managing contaminated wounds.

The potential of pulsed electromagnetic field-generated shock waves for reducing microbial load and improving homogenization in raw milk

Milk is a highly nutritious food essential for human consumption. However, traditional thermal processing methods can reduce its nutritional value and cause unwanted changes. The use of shock waves produced by pulsed electromagnetic fields (PEMFs) has been explored as a means to reduce pathogenic microorganisms. The effect of shock wave treatment on microbial load and particle distribution in packaged fresh cow's milk was investigated. Additionally, the impact of shock wave treatment on Salmonella enterica counts in a bacterial suspension of phosphate-buffered saline (PBS) was evaluated, as this bacterium is a significant milkborne pathogen. Treatment with 1000 impulses from an electromagnetic shock wave generator resulted in a 0.7-log reduction in the total bacterial count of milk. In a separate experiment, a 300-impulse shock wave treatment applied to a Salmonella enterica suspension achieved a 3-log reduction in bacterial counts. Furthermore, shock wave treatment resulted in a decrease in milk particle size compared to untreated milk. Notably, the volume of milk used in this study aligns with commercially available packaged products, enhancing the experiment's industrial relevance. The use of PEMF to generate shock waves could provide a novel approach for future studies focused on reducing the microbial load of milk and improving its homogenization.

Relationship between Particle Size, Anti-Microbial Activity and Leachability of Copper Particles in Liquid Suspension and Compounded in Polypropylene

Testing the antimicrobial efficiency of plastics with good precision and repeatability remains a challenge in the plastic industry, as commonly used standards can provide unreliable data. In this paper, we show that the “Bacterial Liquid Suspension Test” is a reliable method that allows for the measurement of antimicrobial activity of poor to very potent biocides. We used this technique to discriminate the performance of two Cu-based biocides, either in nanoparticle (NP) or macroparticle (MP) size, at three different loadings (0.02, 0.2 and 2 wt.%) in PP. With this technique, we also tested the antibacterial performance of PP as powders, pellets, and injection molded disks. As anticipated, the technique shows that both the increased loading and the smaller particle size showed higher antimicrobial activity than the larger particle size due to their increased surface area. Also, PP powders showed greater bacterial reduction than pellets and disks. While the PP with 2 wt.% Cu NPs showed the best antimicrobial performance, the detection of Cu at the surface (using SEM-EDX) and in the water leachate (using ICP-MS) were below the LODs, indicating their ability to kill bacteria.

Sedimentation dynamics of passive particles in dilute bacterial suspensions: emergence of bioconvection

Microorganisms are ubiquitous in nature and technology. They inhabit diverse environments, ranging from small river tributaries and lakes, to oceans, as well as wastewater treatment plants and food manufacturing. In many of these environments, microorganisms coexist with settling particles. Here, we investigate the effects of microbial activity (swimming E. coli) on the settling dynamics of passive colloidal particles using particle tracking methods. Our results reveal the existence of two distinct regimes in the correlation length scale ( $L_u$ ) and the effective diffusivity of the colloidal particles ( $D_{eff}$ ), with increasing bacterial concentration ( $\phi _b$ ). At low $\phi _b$ , the parameters $L_u$ and $D_{eff}$ increase monotonically with increasing $\phi _b$ . Beyond critical $\phi _b$ , a second regime is found where both $D_{eff}$ and $L_u$ are independent of $\phi _b$ . We demonstrate that the transition between these regimes is characterized by the emergence of bioconvection. We use experimentally measured particle-scale quantities $L_u$ and $D_{eff}$ to predict the critical bacterial concentration for the diffusion–bioconvection transition.

Impact of surface topography and hydrodynamic flow conditions on single and multispecies biofilm formation by Escherichia coli O157:H7 and Listeria monocytogenes in presence of promotor bacteria

Biofilm formation of E. coli O157:H7 and L. monocytogenes in the presence of promotor bacteria R. insidiosa was evaluated on equipment surfaces under different hydrodynamic flow conditions in a Centers for Disease Control and Prevention biofilm reactor (CBR). The CBR containing 330 ml bacterial suspension (6 log CFU/ml in 10% TSB) was used to grow the biofilms on SS 316 L, PTFE, Polycarbonate and EPDM rubber surface coupons under 100, 200 and 300 rpm (shear stresses 0.368, 1.218 and 2.462 N/m2, respectively) for 24 h in batch flow and additional 24 h in continuous flow conditions. Surface roughness and topography of coupons were measured by electron microscopy. Bacterial populations in biofilms were determined by scrapping of coupon surfaces and plating on selective media. Multispecies E. coli O157:H7 biofilm formations were affected by the surface and shear stress. SS, PTFE, and PC exhibited a significant increased biofilm growth at higher shear stress of 2.462 N/m2 compared to 0.368 N/m2. Multispecies L. monocytogenes biofilms formation decreased with increasing shear stress on all the surface materials. Our study emphasizes the importance of surface skewness and kurtosis besides surface's roughness while selecting the material for food processing environments.

Construction of anti-fouling ceramic tubular membranes with corrugated inner surfaces using DLP 3D printing

The challenge of membrane fouling persistently hinders the advancement of membrane technology. The construction of patterned membrane surfaces is anticipated to mitigate the effects of membrane fouling significantly. In this study, ceramic microfiltration membranes with corrugated patterns were fabricated by 3D printing combined with the dip-coating process. To assess the impact of surface patterning on ceramic membrane performance, we initially compared the pore size and pure water flux between straight and corrugated membrane tubes. Both configurations exhibited similar parameters: a support pore size of approximately 1 μm, a membrane layer pore size of about 110 nm, and a pure water permeance of around 950 L m−2 h−1·bar−1. The corrugated ceramic membranes demonstrated superior anti-fouling properties compared to their straight counterparts during the filtration of nanoparticle suspensions, oil-in-water emulsions, and bacterial suspensions. Specifically, under a nanoparticle suspension concentration of 2000 ppm, a transmembrane pressure of 0.2 MPa, and a flow rate of 1.0 m s−1, the corrugated membrane achieved a stable flux of approximately 1.7 times greater than that of the straight membrane. Furthermore, we explored the effects of surface patterning on fluid dynamics through numerical simulations. The enhanced turbulence dissipation rate in the patterned membrane tubes suggests increased surface turbulence and an improved capacity to remove contaminants. This research offers novel insights into the development of ceramic membranes with enhanced anti-fouling capabilities for water treatment.

On the impact of radiative transfer in fluorescence imaging of bacterial films and suspensions

Fluorescence imaging and spectroscopy are convenient, rapid, and simple methods to analyze chemical samples including biological materials such as bacterial biofilms and suspensions. In principle, these techniques could be used to diagnose or discriminate between infectious bacteria in infections of the skin or ocular surface (microbial keratitis, MK). However, the extension of these techniques to macroscopic turbid media that strongly absorb and scatter light is difficult. Radiative transfer effects obscure the relationship between microscopic scattering and absorption properties and macroscopically observable quantities such as fluorescence intensity, transmission, and reflection. A combination of experimental measurements of aqueous bacteria cell suspensions and Monte Carlo radiation transfer simulations are performed to better understand these effects. Several general observations, e.g., that fluorescence intensity is maximized in scattering-dominated media, are discussed in detail. It was found that wavelength-dependent radiative transfer effects are observable even at moderate optical densities (OD ∼ 1; well below the diffusion limit). Careful consideration of radiative transfer effects using physically rigorous models is needed to determine single-cell scattering and absorption properties and interpret quantitative fluorescence measurements accurately in most cases of interest. A detailed discussion of radiative transfer effects and analytical models is provided. In the context of surface infections and MK, it was found that radiative transfer effects may be negligible for the model bacteria E. coli in some cases. However, more accurate measurements of microbe optical properties are needed to confirm and extend this conclusion to other species. Overall this work demonstrates that quantitative fluorescence imaging and spectroscopy of bacterial films and suspensions is feasible, but requires detailed sample characterization and careful consideration of radiative transfer effects.

The Effect of Two Siderophore-Producing Bacillus Strains on the Growth Promotion of Perennial Ryegrass under Cadmium Stress.

Cadmium (Cd) is a highly toxic and cumulative environmental pollutant. Siderophores are heavy metal chelators with high affinity to heavy metals, such as Cd. Ryegrass (Lolium perenne L.) has a potential remediation capacity for soils contaminated by heavy metals. Consequently, using ryegrass alongside beneficial soil microorganisms that produce siderophores may be an effective means to remediate soils contaminated with Cd. In this study, the Bacillus strains WL1210 and CD303, which were previously isolated from the rhizospheres of Nitraria tangutorum in Wulan and Peganum harmala L. in Dachaidan, Qinghai, China, respectively, both arid and sandy environments, were evaluated for heavy metal pollution mitigation. Our quantitative analyses have discerned that the two bacterial strains possess commendable attributes of phosphorus (P) solubilization and potassium (K) dissolution, coupled with the capacity to produce phytohormones. To assess the heavy metal stress resilience of these strains, they were subjected to a cadmium concentration gradient, revealing their incremental growth despite cadmium presence, indicative of a pronounced tolerance threshold. The subsequent phylogenetic analysis, bolstered by robust genomic data from conserved housekeeping genes, including 16S rDNA, gyr B gene sequencing, as well as dnaK and recA, delineated a species-level phylogenetic tree, thereby confirming the strains as Bacillus atrophaeus. Additionally, we identified the types of iron-carrier-producing strains as catechol (WL1210) and carboxylic acid ferrophilin (CD303). A genomic analysis uncovered functional genes in strain CD303 associated with plant growth and iron carrier biosynthesis, such as fnr and iscA. Ryegrass seed germination assays, alongside morphological and physiological evaluations under diverse heavy metal stress, underscored the strains' potential to enhance ryegrass growth under high cadmium stress when treated with bacterial suspensions. This insight probes the strains' utility in leveraging alpine microbial resources and promoting ryegrass proliferation.

Gold Nanoparticle-Based Plasmonic Detection of Escherichia coli, Salmonella enterica, Campylobacter jejuni, and Listeria monocytogenes from Bovine Fecal Samples.

Current diagnostic methods for detecting foodborne pathogens are time-consuming, require sophisticated equipment, and have a low specificity and sensitivity. Magnetic nanoparticles (MNPs) and plasmonic/colorimetric biosensors like gold nanoparticles (GNPs) are cost-effective, high-throughput, precise, and rapid. This study aimed to validate the use of MNPs and GNPs for the early detection of Escherichia coli O157:H7, Salmonella enterica spp., Campylobacter jejuni, and Listeria monocytogenes in bovine fecal samples. The capture efficiency (CE) of the MNPs was determined by using Salmonella Typhimurium (ATCC_13311) adjusted at an original concentration of 1.5 × 108 CFU/mL. One (1) mL of this bacterial suspension was spiked into bovine fecal suspension (1 g of fecal sample in 9 mL PBS) and serially diluted ten-fold. DNA was extracted from Salmonella Typhimurium to determine the analytical specificity and sensitivity/LOD of the GNPs. The results showed that the CE of the MNPs ranged from 99% to 100% and could capture as little as 1 CFU/mL. The LOD of the GNPs biosensor was 2.9 µg/µL. The GNPs biosensor was also tested on DNA from 38 naturally obtained bovine fecal samples. Out of the 38 fecal samples tested, 81.6% (31/38) were positive for Salmonella enterica spp., 65.8% (25/38) for C. jejuni, 55.3% (21/38) for L. monocytogenes, and 50% (19/38) for E. coli O157:H7. We have demonstrated that MNP and GNP biosensors can detect pathogens or their DNA at low concentrations. Ensuring food safety throughout the supply chain is paramount, given that these pathogens may be present in cattle feces and contaminate beef during slaughter.

Antimicrobial Susceptibility Testing for Colistin: Extended Application of Novel Quantitative and Morphologic Assay Using Scanning Electron Microscopy.

Colistin (Polymyxin E) has reemerged in the treatment of MDR Gram-negative infections. Traditional Colistin AST methods have long turnaround times and are cumbersome for routine use. We present a SEM-AST technique enabling rapid detection of Colistin resistance through direct observation of morphological and quantitative changes in bacteria exposed to Colistin. Forty-four Gram-negative reference organisms were chosen based on their Colistin susceptibility profiles. Bacterial suspensions of ∼107 CFU/mL were exposed to Colistin at EUCAST-ECOFF, with controls not exposed, incubated at 37°C, and then sampled at 0, 15, 30, 60, and 120 minutes. Phosphotungstic Acid (PTA) staining was applied, followed by SEM imaging using Hitachi TM4000PlusII-Tabletop-SEM at ×2000, ×5000 and ×7000 magnifications. Bacterial viability analysis was performed for all conditions by quantifying viable and dead organisms based on PTA-staining and morphologic changes. We identified a significant drop in the percentage of viable organisms starting 30 minutes after exposure in susceptible strains, as compared to nonsignificant changes in resistant strains across all tested organisms. The killing effect of Colistin was best observed after 120 minutes of incubation with the antibiotic, with significant changes in morphologic features, including bacterial inflation, fusion, and lysis, observed as early as 30 minutes. Our observation matched the results of the gold standard-based broth microdilution method. We provide an extended application of the proof of concept for the utilization of the SEM-AST assay for Colistin for a number of clinically relevant bacterial species, providing a rapid and reliable susceptibility profile for a critical antibiotic.

Biocontrol of tomato pathogens by Bacillus subtilis F62 and its synergistic action in plant growth promotion with Rhizobium sp. L5

ABSTRACT Plant growth-promoting rhizobacteria (PGPR) are recognised for inhibiting pathogens and increasing plant biomass and yield. This study aims to evaluate the antagonistic potential of Bacillus subtilis F62 against fungal diseases of tomatoes and investigates its capability for promoting the growth of tomato seedlings using single-strain inoculation and co-inoculation with Rhizobium sp. L5. The in vitro antagonism of B. subtilis F62 against Alternaria sp., Botrytis sp., Fusarium sp., and Stemphylium sp. was assessed through dual-culture and volatile compounds assays. Furthermore, the antagonism against Botrytis sp. was also evaluated in harvested tomatoes. The growth promotion experiment involved treating tomato seeds with bacterial suspensions through soil drenching and seed soaking. Our results demonstrated the inhibitory ability of B. subtilis F62 against all fungal species, reducing the mycelial growth speed index from 54.7% to 76.6% in the dual-culture assay, and from 14.1% to 70.6% through antagonism via volatile compounds. This bacterium also decreased the incidence and severity of Botrytis sp. by 21% and 18.8%, respectively, in harvested tomatoes. Additionally, the growth promotion assay revealed that co-inoculation of B. subtilis F62 and Rhizobium sp. L5 increased leaf area and root dry weight compared to single-strain inoculation. Therefore, B. subtilis F62 is a promising bacterium for the biocontrol of tomato diseases and an effective plant growth-promoting rhizobacterium, demonstrating its synergistic effect when co-inoculated with Rhizobium sp. L5 on tomato seeds.

First report of Cassava Bacterial Blight caused by Xanthomonas phaseoli pv. manihotis in the Amazonian forest of Ecuador.

Xanthomonas phaseoli pv. manihotis (Xpm) is a plant pathogenic bacterium known as the causal agent of cassava bacterial blight (CBB). CBB is the most limiting bacterial disease affecting cassava (Manihot esculenta Crantz), characterized by diverse symptoms including angular water-soaked leaf lesions, blight, wilting, stem exudates, stem cankers and dieback. CBB has been reported in most cassava-growing regions around the world, and, under conducive conditions, crop yield losses can reach up to 100% (Zárate-Chaves et al. 2021). While Xpm genetic diversity is remarkably high in South America (Bart et al. 2012) and cassava originates and was domesticated in the Amazon basin (Allem 2002), reports of CBB in the Amazonian region are missing. To fill this gap, in October 2018 we surveyed for CBB symptoms in cassava fields of the Orellana Province, located in the Amazon forest of the Republic of Ecuador. Adult cassava plants exhibiting typical angular, water-soaked leaf lesions were found in polyculture plots, i.e. intercrops of cassava with other species such as plantains and fruit trees (a.k.a. chakras). After surface disinfection with 5% sodium hypochlorite followed by 70% ethanol, white Xpm-like colonies were isolated from diseased leaf tissues of four plants on YPGA medium (yeast extract, 5 g/l; peptone, 5 g/l; glucose, 5 g/l; agar-agar, 15 g/l) supplemented with cephalexin (40 mg/l) and cycloheximide (50 mg/l). Pathogenicity tests were performed on peat-potted, 2-month-old cassava plants of the cultivar 60444. Bacterial suspensions were adjusted to an OD600 of 0.2 (2 × 108 CFU/ml) in sterile 10-mM MgCl2 and syringe infiltrated in fully-expanded leaves. In parallel, 20 µl of each bacterial suspension adjusted to an OD600 of 0.02 (2 × 107 CFU/ml) were inoculated on stems inside a hole previously punched with a sterile needle in the junction of the third-top petiole. Sterile 10-mM MgCl2 was used for mock inoculations in both leaves and stems, and experiments were replicated in three plants. Plants were incubated in a greenhouse at 28 ± 1°C with a 12-h photoperiod. Infiltrated leaves developed watersoaking 3 days post inoculation, while wilted leaves, stem exudates, and dieback were observed 21 days after stem inoculation. Control plants remained symptomless. White Xpm-like colonies were re-isolated from symptomatic leaves (Fig S1). One colony of each of the four Xpm isolates (before and after re-isolation) was assessed using diagnostic PCRs (Bernal-Galeano et al. 2018; Flores et al. 2019), using strain Xam668 as positive control. All four candidates were positive for both diagnostic tools. The sequences of the housekeeping genes atpD, dnaK, efp, glnA, gyrB and rpoD of our isolates were extracted from full genome sequences obtained through Oxford Nanopore Technologies (ONT) (GenBank OR288194 to OR288217) and compared to their homologs in four close Xanthomonas species and a reference Xpm strain (Table S1). The sequences of the tested strains aligned with that of Xpm CIO151 (GCA_004025275.1) (Arrieta-Ortiz et al. 2013) with nucleotide identity above 99.92% (Fig S2). The four strains were named CIX4169, CIX4170, CIX4171 and CIX4172, stored in the IRD Collection of Xanthomonas, where they are available upon request. To our knowledge, this is the first report of CBB in the Amazonian region and in Ecuador, where cassava is a central element for local culture and economy. Further surveys will be necessary to evaluate the distribution and prevalence of CBB in other ecozones of Ecuador where cassava is cultivated.

Microbiological Mechanisms of Collaborative Remediation of Cadmium-Contaminated Soil with Bacillus cereus and Lawn Plants.

Severe cadmium contamination poses a serious threat to food security and human health. Plant-microbial combined remediation represents a potential technique for reducing heavy metals in soil. The main objective of this study is to explore the remediation mechanism of cadmium-contaminated soil using a combined approach of lawn plants and microbes. The target bacterium Bacillus cereus was selected from cadmium-contaminated soil in mining areas, and two lawn plants (Festuca arundinacea A'rid III' and Poa pratensis M'idnight II') were chosen as the target plants. We investigated the remediation effect of different concentrations of bacterial solution on cadmium-contaminated soil using two lawn plants through pot experiments, as well as the impact on the soil microbial community structure. The results demonstrate that Bacillus cereus promotes plant growth, and the combined action of lawn plants and Bacillus cereus improves soil quality, enhancing the bioavailability of cadmium in the soil. At a bacterial suspension concentration of 105 CFU/mL, the optimal remediation treatment was observed. The removal efficiency of cadmium in the soil under Festuca arundinacea and Poa pratensis treatments reached 33.69% and 33.33%, respectively. Additionally, the content of bioavailable cadmium in the rhizosphere soil increased by up to 13.43% and 26.54%, respectively. Bacillus cereus increased the bacterial diversity in the non-rhizosphere soil of both lawn plants but reduced it in the rhizosphere soil. Additionally, the relative abundance of Actinobacteriota and Firmicutes, which have potential for heavy metal remediation, increased after the application of the bacterial solution. This study demonstrates that Bacillus cereus can enhance the potential of lawn plants to remediate cadmium-contaminated soil and reshape the microbial communities in both rhizosphere and non-rhizosphere soils.

Staphylococcus aureus–specific skin resident memory T cells protect against bacteria colonization but exacerbate atopic dermatitis–like flares in mice

BackgroundThe contribution of Staphylococcus aureus (S. aureus) to the exacerbation of atopic dermatitis (AD) is widely documented, but its role as a primary trigger of AD skin symptoms remains poorly explored. ObjectiveTo reappraise the main bacterial factors and underlying immune mechanisms by which S. aureus triggers AD-like inflammation. MethodsWe capitalized on a pre-clinical model, in which different clinical isolates were applied in the absence of any prior experimental skin injury. ResultsWe report that the development of S. aureus-induced dermatitis depended on the nature of the S. aureus strain, its viability, the concentration of the applied bacterial suspension, the production of secreted and non-secreted factors, as well as the activation of accessory gene regulatory quorum sensing system. In addition, the rising dermatitis, which exhibited the well-documented AD cytokine signature, was significantly inhibited in inflammasome adaptor protein ASC- and monocyte/macrophage-deficient animals, but not in T- and B-cell-deficient mice, suggesting a major role for the innate response in the induction of skin inflammation. However, bacterial exposure generated a robust adaptive immune response against S. aureus, and an accumulation of S. aureus-specific γδ and CD4+ tissue resident memory T (Trm) cells at the site of previous dermatitis. The latter both contributed to worsen the flares of AD-like dermatitis upon new bacteria exposures, but also, protected the mice from persistent bacterial colonization. ConclusionThese data highlight the induction of unique AD-like inflammation, with the generation of pro-inflammatory but protective Trm cells in a context of natural exposure to pathogenic S. aureus strains.

A new bacterial concentration method for large-scale applications of biomineralization

Bacterial suspension is an essential component of microbially induced carbonate precipitation (MICP)-based biocement and a large-scale production is required for field applications. In this study, a new bacterial concentration method is proposed to enable high concentration bacterial suspension to be produced to facilitate field work. By adding low concentration calcium to bacterial suspension, flocs are formed and bacterial cells are adsorbed on the flocs to achieve bacterial concentration. Compared to the traditional bacterial concentration method using centrifugation and freezing-drying method, the proposed method can concentrate a large volume of bacterial suspension without using special equipment. The feasibility of this method is verified by bacterial concentration tests, solution tests and sand column treatment tests. The results of both the solution test and the sand column treatment test show that the bacterial suspension concentrated by the proposed method can be effectively used for soil biocementation. There is a threshold calcium concentration that allows a complete bacterial concentration for the proposed method, and this threshold calcium concentration tends to increase linearly with the optical density of the cell suspension at a wavelength of 600 nm (OD600).

Optimisation of plasma-activated water: Plasma DBD technology and application in recirculating aquaculture system for Nile tilapia larval culture

Plasma-activated water (PAW) is a useful tool for producing pathogen-free seed fish. This study aimed to apply dielectric barrier discharge (DBD) plasma to reduce the microbial population in the water of a recirculating aquaculture system (RAS) for Nile tilapia larval culture. Initially, a PAW system prototype was developed and found to effectively reduce bacterial populations in both stagnant and circulating water. Additionally, a slight increase in water temperature was observed in the circulating water. Subsequently, the optimisation of PAW conditions in the circulating water was performed. The PAW system, with a copper anode distance of 2 cm and a 1 cm distance between the copper tip and the water surface, combined with a non-spaced cathode pad, exhibited the highest bactericidal effect. Using the optimised PAW conditions, for Experiment I, Nile tilapia larval culture was established in the RAS, supplemented with a bacterial suspension (Bacillus subtilis, Streptococcus agalactiae and Aeromonas hydrophila) to assess the bactericidal effects. Three treatments were applied: 1) control (no PAW or antibiotics), 2) PAW, and 3) antibiotic treatment for Nile tilapia larvae cultured in the RAS system for 672 h. The results demonstrated that both PAW and antibiotic treatments significantly reduced the bacterial populations in the water in relation to the control (P < 0.05). Moreover, a substantial reduction in bacterial population was observed in the whole body of the fingerlings in both the PAW and antibiotic groups in relation to the control fingerlings (P < 0.05). In Experiment II, Nile tilapia larval culture in the RAS was conducted under three different conditions: 1) control (no PAW or antibiotic), 2) PAW, and 3) antibiotic treatment, to evaluate the antimicrobial effects of PAW on waterborne bacterial populations for 672 h. Similar to Experiment I, both antibiotic and plasma treatments significantly reduced the bacterial populations in the water and whole-body fingerlings in relation to the control (P < 0.05). Notably, the growth performance and whole-body composition (moisture, crude protein, crude fat, and ash) of the fingerling fish appeared comparable among the experimental groups (P > 0.05), suggesting that PAW had no detrimental effects on long-term fish culture. Therefore, PAW can be employed to effectively reduce bacterial populations in water, thus minimising bacteria-related issues in fish without adverse impacts on fish growth.

Pathogens of the oak processionary moth Thaumetopoea processionea: Developing a user-friendly bioassay system and metagenome analyses for microorganisms

The oak processionary moth (OPM) Thaumetopoea processionea is a pest of oak trees and poses health risks to humans due to the urticating setae of later instar larvae. For this reason, it is difficult to rear OPM under laboratory conditions, carry out bioassays or examine larvae for pathogens. Biological control targets the early larval instars and is based primarily on commercial preparations of Bacillus thuringiensis ssp. kurstaki (Btk). To test the entomopathogenic potential of other spore-forming bacteria, a user-friendly bioassay system was developed that (i) applies bacterial spore suspensions by oak bud dipping, (ii) targets first instar larvae through feeding exposure and (iii) takes into account their group-feeding behavior. A negligible mortality in the untreated control proved the functionality of the newly established bioassay system. Whereas the commercial Btk HD-1 strain was used as a bioassay standard and confirmed as being highly efficient, a Bacillus wiedmannii strain was ineffective in killing OPM larvae. Larvae, which died during the infection experiment, were further subjected to Nanopore sequencing for a metagenomic approach for entomopathogen detection. It further corroborated that B.wiedmannii was not able to infect and establish in OPM, but identified potential insect pathogenic species from the genera Serratia and Pseudomonas.

First Report of Dickeya dadantii Causing Potato Blackleg in Fujian Province China.

Blackleg and soft rot are harmful diseases in potato (Solanum tuberosum) caused by Pectobacterium spp. and Dickeya spp. (Czajkowski et al. 2015). The occurrence of potato blackleg was serious in potato-producing areas around Xiapu County in Fujian Province, China, in 2021 (6 ha) and 2022 (7 ha), with an incidence of approximately 5%, which reached nearly 23%. Three diseased plants were collected to isolate the pathogen. Single colonies from each sampled plant were isolated and streaked onto fresh plates. DNA from three colonies from different plants was PCR amplified with primer pair 27F/1492R (Lane 1991) for the 16S rRNA gene. Since the sequences were identical, we selected strain M2-3 for further analysis. The strain M2-3 was gram-negative, pectolytic on CVP, grew at 37°C and 5% NaCl. The bacterium was positive for phosphatase activity, erythromycin sensitivity, indole production, gelatin liquefaction, malonic utilization, and acid production from, melibiose, raffinose, and arabinose. The bacterium was negative for sucrose, α-methyl glucoside, sorbitol, trehalose, lactose, and sodium citrate (Fujimoto et al. 2018;),although sucrose and lactose did not provide the expected results, there are exception in all species. The genome of strain M2-3 was sequenced and deposited in the NCBI database under accession numbers: CP077422. An Average Nucleotide Identity (ANI) analysis showed that M2-3 clustered with other D. dadantii strains and has a 98.39% identity with D. dadantii strain DSM 18020 (CP023467). The housekeeping genes (recA, dnaX, acnA, gapA, icd, mdh, mtlD and pgi) were amplified with primer pairs designed previously(Fujimoto et al. 2018; Ma et al. 2007) and sequenced. A multilocus sequence analysis (MLSA) was performed by concatenating the 8 gene sequences and constructing a maximum likelihood phylogenetic tree using PhyloSuite version 1.2.1 (Zhang et al. 2020) and IQ-tree version 1.6.8 (Nguyen et al. 2015) software. Strain M2-3 was clustered together with Dickeya dadantii. For the pathogenicity test, three plants per treatment, totaling nine plants, were used. Bacterial suspensions (1×10^8 CFU/mL) were made in a 10mM PBS buffer. 10 μL of M2-3, D. dadantii type strain 18020 (positive control), and buffer (negative control) were injected into the plant stems near the base. Water stains appeared at the site of inoculation after 2 days and they gradually became black and rotten. The leaves became yellow and wilted, and the petiole base rotted within 5 days of inoculation completing the Koch postulate. According to average nucleotide identity and housekeeping gene sequence analysis, strain M2-3 was identified as Dickeya dadantii. Previous studies have reported several pathogens that cause potato blackleg in China, including P. atrosepticum, P. carotovorum, P. brasiliense, P. parmentieri, P. polaris, and P. punjabense (Li-ping et al. 2020; Wang et al. 2021). To the best of our knowledge, this study is the first to report potato blackleg disease caused by Dickeya dadantii in Fujian Province, China. This finding suggests that this pathogen may cause a threat to potato production in Fujian Province.

Bacillus velezensis YXDHD1-7 Prevents Early Blight Disease by Promoting Growth and Enhancing Defense Enzyme Activities in Tomato Plants.

Bacillus velezensis is well known as a plant growth-promoting rhizobacteria (PGPR) and biocontrol agent. Nevertheless, there are very few reports on the study of B. velezensis on tomato early blight, especially the biocontrol effects among different inoculation concentrations. In this study, an IAA-producing strain, Bacillus velezensis YXDHD1-7 was isolated from the tomato rhizosphere soil, which had the strongest inhibitory effect against Alternaria solani. Inoculation with bacterial suspensions of this strain promoted the growth of tomato seedlings effectively. Furthermore, inoculations at 106, 107, and 108 cfu/mL resulted in control efficacies of 100%, 83.15%, and 69.90%, respectively. Genome sequencing showed that it possesses 22 gene clusters associated with the synthesis of antimicrobial metabolites and genes that are involved in the production of IAA. Furthermore, it may be able to produce spermidine and volatile compounds that also enhance plant growth and defense responses. Our results suggest that strain YXDHD1-7 prevents early blight disease by promoting growth and enhancing the defense enzyme activities in tomato plants. This strain is a promising candidate for an excellent microbial inoculant that can be used to enhance tomato production.