Transport of Pseudomonas aeruginosa in Polymer Solutions

Bacteria often live surrounded by polymer solutions, such as in animal respiratory, gastrointestinal, and reproductive tracts. In these systems, polymer solutions are often exposed to fluid flow, and their complex rheology can affect the transport of chemical compounds and microorganisms. Recent studies have focused on the effect of polymer solutions on the motility of bacteria in the absence of fluid flow. However, flow can be a game-changer on bacterial transport, as demonstrated by the depletion of motile bacteria from the low-shear regions and trapping in the high-shear regions in simple fluids, even for flows as simple as the Poiseuille one. Despite the relevance of polymer solutions in many bacterial habitats, the effect of their complex rheology on shear-induced trapping and bacterial transport in flow has remained unexplored. Using microfluidic experiments and numerical modeling, we studied how the shear rate and the rheological behavior of Newtonian and non-Newtonian polymer solutions affect the transport of motile, wild-type Pseudomonas aeruginosa in a Poiseuille flow. Our results show that, in Newtonian solutions, an increase in viscosity reduces bacterial depletion in the low-shear regions at the microchannel center, due to a reduction in the bacterial swimming velocity. Conversely, in the non-Newtonian solution, we observed a depletion comparable to the buffer case, despite its zero-shear viscosity being two orders of magnitude higher. In both cases, bacterial swimming and polymer fluid rheology control the magnitude of bacterial depletion and its shear-rate dependence. Our observations underscore the importance of the rheological behavior of the carrier fluid in controlling bacterial transport, in particular, close to surfaces giving rise to velocity gradients, with potential consequences on surface colonization and biofilm formation in many naturally relevant microbial habitats

Preservatives accelerate the horizontal transfer of plasmid-mediated antimicrobial resistance genes via differential mechanisms

Increasing concentrations of preservatives have been detected in environments due to the overuse and misuse of preservatives in food and personal care products. Recent studies have relied heavily on the toxicity, biodegradability, and fate of preservatives in the environment. However, the biological effects of preservatives on antimicrobial resistance, which poses great threats to public health worldwide, are largely unknown. This study investigated three preservatives for their ability and mechanisms of promoting horizontal transfer of antimicrobial resistance genes (ARGs). The results demonstrated that these preservatives (sodium nitrite, sodium benzoate, and triclocarbon), under daily-use concentrations, led to concentration-dependent increases in conjugative transfer by 1.24–2.63, 6.79–7.05, and 2.17–4.31 folds compared with the control group. Even these three preservatives had different patterns on generating intracellular reactive oxidative species (ROS) and reactive nitrogen species (RNS), all of them could stimulate radical-induced RpoS regulon and SOS response, increase cell membrane permeability, and regulate conjugative transfer-related genes, subsequently promoting horizontal transfer of ARGs. The present results expanded the understanding of biological effects induced by preservatives, and provided mechanistic insight into the preservatives-induced resistance. This study also opens an intriguing question on the roles of emerging contaminants including preservatives in the emerging and spread of ARGs in various environments.ISSN:0160-4120ISSN:1873-675

(Comparison of feeding behaviors and pathogen acquisition rates of adults and the 5th instar nymphs of Diaphorina citri (Hemiptera: Liviidae) on huanglongbing-infected citrus plants)

Aim: The Asiatic citrus psyllid (ACP), Diaphorina citri, is the major vector of ‘Candidatus Liberibacter asiaticus’ (‘CLas’) (α-Proteobacteria), the pathogen that causes the Asiatic form of huanglongbing (HLB), the most devastating disease of citrus. The aims of this study are to determine whether the feeding behaviors of adults and the 5th instar nymphs of D. citri differ, and if so, whether these differences influence pathogen acquisition efficiency, and whether HLB-infected plants influence feeding by the 5th instar nymphs. Methods: The feeding behavior of adults and the 5th instar nymphs of D. citri on immature shoots of HLB-infected Citrus reticulata cv. Sunki was recorded for 10 h with DC-EPG giga-4. The acquisition efficiency of the pathogen by individual adults and nymphs from HLB-infected shoots was determined by qPCR. The feeding behaviors of the 5th instar nymphs on pathogen-free and HLB-infected shoots were also recorded and compared by EPG. Results: The feeding behaviors of adults and the 5th instar nymphs of D. citri on C. reticulata cv. Sunki shoots infected with HLB differed significantly. The 5th instar nymphs started to ingest xylem and phloem sap sooner than adults. Durations of the phloem salivation and ingestion phases of nymphs were significantly longer than those of adults. When feeding on HLB-infected shoots, 37.5% of the 5th instar nymphs acquired ‘CLas’ in contrast 20% of adults. The frequencies of probing and salivation and phloem sap ingestion by the 5th instar nymphs feeding on HLB-infected shoots were significantly lower than those on healthy shoots. However, HLB-infected plants did not influence the duration of phloem salivation and sap ingestion by the 5th instar nymphs. Feeding also commenced sooner in phloem of HLB-infected shoots than in phloem of healthy shoots. Conclusion: The 5th instar nymphs of D. citri feed for longer intervals, ingest more phloem sap, and acquire higher titers of ‘CLas’ than adults. This may be due to that nymphs require more nutrients for their growth and development than adults. They are therefore less inclined to withdraw their stylets from, and re-insert their stylets into ‘CLas’-infected leaf tissues. ‘CLas’-induced changes in host-plant phytochemistry promote feeding by the 5th instar nymphs of D. citri

Airborne metal nanoparticles released by azides detonation: determination and potential public exposure

Abstract Metal azides are highly energetic materials that release a large amount of gas upon detonation. They also release metal particles, generating an aerosol. The most common azide is sodium azide (NaN3), which is used nowadays in car airbags. If the decomposition is not complete, harmful azide particles might be inhaled. Heavy metal azides find application as a primary explosive (primer) in ammunition. Public health officials have raised concerns about heavy metal particles released during training in shooting ranges. We identify a lack of knowledge on airborne metal particles properties released from azide detonation and on the analytical methods applied to characterize them. As a case study, we detonated milligram amounts of silver azide, copper azide, and a mixture of them in a glove box. We then analyse the airborne particles with an ensemble analytical setup, able to measure real-time their particle size distribution and chemical composition. We detected spherical metal nanoparticles in the range of 2–500 nm. These findings and the developed analytical tools may allow identifying airborne nanoparticles the passenger compartments of vehicles after airbag activation as well as in indoor shooting ranges, contributing to the evaluation of public health risks

Dilution versus fractionation: Separation technologies hyphenated with spICP-MS for characterizing metallic nanoparticles in aerosols

The presence of metal salts has become one of the major limitations for measuring metallic nanoparticles (NPs) in single particle inductively coupled plasma mass spectrometry (spICP-MS). Their presence generates a background signal in spICP-MS that can be overlapped with the signal intensity of small particles, leading to inaccurate NP size distributions. To overcome this analytical problem, sample pretreatment methods (e.g. dilution or fractionation) have been applied to liquid samples before spICP-MS measurements to minimize the ionic interference. However, the number of studies focused on reducing the presence of metal salts in aerosol characterization is limited. In this contribution, we investigated three different technologies coupled to an ICP-MS for online separating metallic NPs signals from ionic interference signals of metal salts in the aerosol. A rotating disk diluter (RDD) was used for the online dilution of the aerosol, while a differential mobility analyzer (DMA) and a centrifugal particle mass analyzer (CPMA) were used for the online fractionation of specific-sized NPs in the aerosol. The results from the analysis of 100 nm gold NPs (AuNPs) mixed with gold salts (Au3+, mass ratio 1:25) showed the particle size limit of detection decreased from 78 nm to 61, 50, and 33 nm by using RDD, CPMA, and DMA respectively. In addition, it was found that the separation performance of AuNPs was in the order of DMA > RDD > CPMA. The methods used in this study based on spICP-MS have the potential to characterize directly NPs in complex aerosols containing metal salts.ISSN:0021-8502ISSN:1879-196

An elution-based method for estimating efficiencies of aerosol collection devices not affected by their pressure drops

The evaluation of collection efficiencies of aerosol samplers becomes challenging with high pressure drops. The evaluation approaches applied at various conditions deserve further development, especially when a high pressure drop is induced by the sampler. In this work, an elution-based method using NaCl aerosol was proposed to estimate the size-resolved collection efficiency which was not affected by the pressure drop. More specifically, a Condensation Particle Counter (CPC) was used to count the upstream particle number, and the collected NaCl particles were eluted and determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for estimating the collected particle number. The relationship between number-based concentration and mass-based concentration of NaCl particles was established. A stainless steel impactor for Differential Mobility Analyzer (DMA), polydimethylsiloxane (PDMS)-based microchannel, and a homemade impactor containing 151 nozzles with a diameter of 0.1 mm were employed to investigate the feasibility of the elution method. DMA-selected particles with a nominal size are considered to be the monodisperse aerosol, which was commonly used for estimating the collection efficiencies of samplers, but size redistribution of downstream monodisperse aerosol with the particle size smaller than 100 nm and larger than the cutoff size (D50) was revealed through the elution method, which affected the collection efficiency measured by either conventional CPC- or elution-based method. It was found that the elution method was dependent on the D50 value of the sampler, and the applicable size range was from 100 nm to D50 (D50 < 500 nm) or from 100 nm to 500 nm (D50 greater than 500 nm). This study provided insights into the size-dependent particle transport through aerosol samplers, and the development of an elution-based method to estimate pressure drop-independent collection efficiencies.ISSN:1383-586

Transport of Pseudomonas aeruginosa in Polymer Solutions

Bacteria often live surrounded by polymer solutions, such as in animal respiratory, gastrointestinal, and reproductive tracts. In these systems, polymer solutions are often exposed to fluid flow, and their complex rheology can affect the transport of chemical compounds and microorganisms. Recent studies have focused on the effect of polymer solutions on the motility of bacteria in the absence of fluid flow. However, flow can be a game-changer on bacterial transport, as demonstrated by the depletion of motile bacteria from the low-shear regions and trapping in the high-shear regions in simple fluids, even for flows as simple as the Poiseuille one. Despite the relevance of polymer solutions in many bacterial habitats, the effect of their complex rheology on shear-induced trapping and bacterial transport in flow has remained unexplored. Using microfluidic experiments and numerical modeling, we studied how the shear rate and the rheological behavior of Newtonian and non-Newtonian polymer solutions affect the transport of motile, wild-type Pseudomonas aeruginosa in a Poiseuille flow. Our results show that, in Newtonian solutions, an increase in viscosity reduces bacterial depletion in the low-shear regions at the microchannel center, due to a reduction in the bacterial swimming velocity. Conversely, in the non-Newtonian solution, we observed a depletion comparable to the buffer case, despite its zero-shear viscosity being two orders of magnitude higher. In both cases, bacterial swimming and polymer fluid rheology control the magnitude of bacterial depletion and its shear-rate dependence. Our observations underscore the importance of the rheological behavior of the carrier fluid in controlling bacterial transport, in particular, close to surfaces giving rise to velocity gradients, with potential consequences on surface colonization and biofilm formation in many naturally relevant microbial habitats.ISSN:2296-424

Integrated Aerodynamic/Electrochemical Microsystem for Collection and Detection of Nanogram-level Airborne Bioaccessible Metals

The soluble fraction of aerosol particulate matter containing trace metals has the potential to engender toxicity and exacerbate the adverse health effects of particulate matter. In this study, an inertial-impaction-based fluidic chip integrated with electrochemical detection was developed to achieve high collection efficiency and measurements of the bioaccessible metal fraction at the nanogram level. The average collection efficiency for ultrafine and fine particles larger than 50 nm, obtained at a flow rate of 2.5 L/min, was above 70%. The detection ranges of aerosol soluble copper depended on the collection duration and airflow rate. At a working flow rate of 3.1 L/min and collection efficiency of 70%, the microsystem was capable of detecting Cu concentrations above 53 ng/m3, 32 ng/m3 and 8 ng/m3 with 3 h, 5 h and 20 h collection periods, respectively, which were in the range of reported atmospheric concentrations. The detection ratio of real-world samples (i.e. PM10-like aerosol) was 100 ± 14%, indicating excellent aerodynamic collection and reliable electrochemical detection. The collection and sensing performance of the microsystem demonstrates a new step towards an online, mobile, low-cost, and miniaturized routine monitoring system for bioaccessible metals and possibly other soluble components in the aerosols

Integrated aerodynamic/electrochemical microsystem for collection and detection of nanogram-level airborne bioaccessible metals

The soluble fraction of aerosol particulate matter containing trace metals has the potential to engender toxicity and exacerbate the adverse health effects of particulate matter. In this study, an inertial-impaction-based fluidic chip integrated with electrochemical detection was developed to achieve high collection efficiency and measurements of the bioaccessible metal fraction at the nanogram level. The average collection efficiency for ultrafine and fine particles larger than 50 nm, obtained at a flow rate of 2.5 L/min, was above 70%. The detection ranges of aerosol soluble copper depended on the collection duration and airflow rate. At a working flow rate of 3.1 L/min and collection efficiency of 70%, the microsystem was capable of detecting Cu concentrations above 53 ng/m3, 32 ng/m3 and 8 ng/m3 with 3 h, 5 h and 20 h collection periods, respectively, which were in the range of reported atmospheric concentrations. The detection ratio of real-world samples (i.e. PM10-like aerosol) was 100 ± 14%, indicating excellent aerodynamic collection and reliable electrochemical detection. The collection and sensing performance of the microsystem demonstrates a new step towards an online, mobile, low-cost, and miniaturized routine monitoring system for bioaccessible metals and possibly other soluble components in the aerosols.ISSN:0925-400

Breaking Down the Performance Losses in O₂-Evolution Stability Tests of IrO₂-based Electrocatalysts

Understanding the deactivation mechanisms affecting the state-of-the-art, Ir oxide catalysts employed in polymer electrolyte water electrolyser (PEWE-) anodes is of utmost importance to guide catalyst design and improve PEWE-durability. With this motivation, we have tried to decouple the contributions of various degradation mechanisms to the overall performance losses observed in rotating disk electrode (RDE) tests on three different, commercial Ir oxide catalysts (pure or supported on Nb2O5). Specifically, we investigated whether these performance decays stem from an intrinsic deactivation of the catalysts caused by alterations in their oxidation state, crystalline structure, morphology and/or Ir-dissolution, and also assessed possible decreases in the catalyst loading caused by the delamination of the materials over the course of these OER-stability tests. Additionally, we also examined recently reported artifacts related to the use of RDE voltammetry for such measurements and found that neither these nor the above mechanisms (or combinations thereof) can cause the totality of the observed performance losses. Beyond these uncertainties, complementary PEWE-tests showed that this apparent RDE-instability is not reproduced in this application-relevant environment.ISSN:0013-4651ISSN:1945-711