Ultrasound-Induced Escherichia coli O157:H7 Cell Death Exhibits Physical Disruption and Biochemical Apoptosis

Comparison of Power Ultrasound and NALC-NaOH Decontamination Methods for Stool Mycobacterial Culture: A Prospective Study

Stool samples have been reported to be useful for the diagnosis of pulmonary tuberculosis (PTB), especially in patients who are unable to produce sputum. However, contamination limits the usefulness of stool specimens in mycobacterial culture. In this study, a novel decontamination method of power ultrasound (PU) was evaluated for mycobacterial isolation from suspected PTB cases. Stool samples (n = 650) were collected, and each sample was divided into approximately three equal groups. In addition to an AFB smear (Auramine O method), the stool samples were treated using different decontamination methods (NaOH-NALC vs. PU methods). The sensitivity (calculated against CRS) and contamination rates between the two methods were compared using McNemar's test. Of the 650 samples, 32 (4.92%) stool samples treated with the NaOH-NALC method were culture-positive, including Mycobacterium tuberculosis (M.TB; n = 21, 3.23%) and nontuberculous mycobacteria (NTM; n = 11, 1.69%). Sixty-one (9.38%) stool samples treated with the PU method were culture-positive, including M.TB (n = 37, 5.69%) and NTM (n = 24, 3.69%). Statistical analysis showed that a significant difference was found in the isolation rate of M.TB and NTM between the two methods (p < 0.05). Additionally, compared with the NALC-NaOH method (19.07%), stool samples treated with the PU method (13.23%) had a significantly lower contamination rate (p < 0.05). In conclusion, our findings suggest that the utilization of the PU method as a novel decontamination technique could significantly enhance the isolation rates of both NTM and M.TB when stool specimens are employed for culture. Compared to the NaOH-NALC method, this approach proves to be more effective in facilitating stool mycobacterial culture.

Chickpea-Derived Modified Antimicrobial Peptides KTA and KTR Inactivate Staphylococcus aureus via Disrupting Cell Membrane and Interfering with Peptidoglycan Synthesis

The widespread bacterial contamination caused by foodborne pathogens has continuously driven the development of advanced and potent food antimicrobial agents. In this study, two novel antimicrobial peptides (AMPs) named KTA and KTR were obtained by modifying a natural AMP, Leg2, from chickpea storage protein legumin hydrolysates. They were further predicted to be stable hydrophobic cationic AMPs of α-helical structure with no hemolytic toxicity by several online servers. Moreover, the AMPs exerted superior antibacterial activity against two representative Staphylococcus aureus strains thanks to the increased hydrophobicity and positive charge, with minimum inhibition concentration value (4.74-7.41 μM) significantly lower than that of Leg2 (>1158.70 μM). Further, this study sought to elucidate the specific antimicrobial mechanism against Gram-positive bacteria. It was found that the electrostatic interactions of the AMPs with peptidoglycan were vital for peptide activity in combating Gram-positive bacteria. Subsequently, the cell membrane of S. aureus cells was irreversibly disrupted by increasing permeability and impairing membrane components, which led to the massive release of intracellular substances and eventual cell death. Overall, this work demonstrated that KTA and KTR were active against Gram-positive bacteria via peptidoglycan targeting and membrane-disruptive mechanisms and paved the way for expanding their application potential to alleviate food contamination.

Ultrasonic cavitation induced Vibrio parahaemolyticus entering an apoptosis-like death process through SOS response

As an effective non-thermal sterilization method, ultrasound remains at the level of passive bacterial death despite the initial understanding of its sterilization mechanism. Here, we present the perspective that bacteria can choose to actively enter an apoptosis-like death state in response to external ultrasonic stress. In this study, Vibrio parahaemolyticus exhibited apoptotic markers such as phosphatidylserine ectropion and activated caspases when subjected to ultrasound stress. Additionally, the accumulation of reactive oxygen species (ROS) and enhanced calcium signaling were observed. Further transcriptomic analysis was conducted to investigate the regulatory mechanism of the SOS response in Vibrio parahaemolyticus during an apoptosis-like state. The results showed that the genes encoding the citrate cycle were down-regulated in Vibrio parahaemolyticus cells adapted to ultrasonic stress, leading to an apoptosis-like state and a decrease in production capacity and ability to catabolize carbon dioxide. Furthermore, the level of oxidized glutathione increased, suggesting that the bacteria were engaged in various anti-oxidative stress responses, ultimately leading to apoptosis. Moreover, the ultrasound field activated the regulatory factor CsrA, which facilitates stress survival as cells transition from rapid growth to an apoptotic state through a stringent response and catabolic inhibition system. Parallel reaction monitoring (PRM) revealed that the expression of certain key SOS proteins in Vibrio parahaemolyticus was up-regulated following ultrasound treatment, resulting in a gradual adaptation of the cells to external stress and ultimately leading to active cell death. In conclusion, the biological lethal effect of ultrasound treatment is not solely a mechanical cell necrosis process as traditionally viewed, but also a programmed cell death process regulated by cellular adaptation. This enriched the biological effect pathway of ultrasound sterilization.

Ultrasound meets the cell membrane: for enhanced endocytosis and drug delivery

Endocytosis plays a crucial role in drug delivery for precision therapy. As a non-invasive and spatiotemporal-controllable stimulus, ultrasound (US) has been utilized for improving drug delivery efficiency due to its ability to enhance cell membrane permeability. When US meets the cell membrane, the well-known cavitation effect generated by US can cause various biophysical effects, facilitating the delivery of various cargoes, especially nanocarriers. The comprehension of recent progress in the biophysical mechanism governing the interaction between ultrasound and cell membranes holds significant implications for the broader scientific community, particularly in drug delivery and nanomedicine. This review will summarize the latest research results on the biological effects and mechanisms of US-enhanced cellular endocytosis. Moreover, the latest achievements in US-related biomedical applications will be discussed. Finally, challenges and opportunities of US-enhanced endocytosis for biomedical applications will be provided.

Microbial decontamination assisted by ultrasound-based processing technologies in food and model systems: A review

Ultrasound (US) technology is recognized as one of the emerging technologies that arise from the current trends for improving nutritional and organoleptic properties while providing food safety. However, when applying the US alone, higher power and longer treatment times than conventional thermal treatments are needed to achieve a comparable level of microbial inactivation. This results in risks, damaging food products' composition, structure, or sensory properties, and can lead to higher processing costs. Therefore, the US has often been investigated in combination with other approaches, like heating at mild temperatures and/or treatments at elevated pressure, use of antimicrobial substances, or other emerging technologies (e.g., high-pressure processing, pulsed electric fields, nonthermal plasma, or microwaves). A combination of US with different approaches has been reported to be less energy and time consuming. This manuscript aims to provide a broad review of the microbial inactivation efficacy of US technology in different food matrices and model systems. In particular, emphasis is given to the US in combination with the two most industrially viable physical processes, that is, heating at mild temperatures and/or treatments at elevated pressure, resulting in techniques known as thermosonication, manosonication, and manothermosonication. The available literature is reviewed, and critically discussed, and potential research gaps are identified. Additionally, discussions on the US's inactivation mechanisms and lethal effects are included. Finally, mathematical modeling approaches of microbial inactivation kinetics due to US-based processing technologies are also outlined. Overall, this review focuses only on the uses of the US and its combinations with other processes relevant to microbial food decontamination.

Ultrasonic interfacial crosslinking of TiO2-based nanocomposite hydrogels through thiol-norbornene reactions for sonodynamic antibacterial treatment

Nanocomposite (NC) hydrogels used for sonodynamic therapy (SDT) face challenges such as lacking interfacial interactions between the polymers and nanomaterials as well as presenting uneven dispersion of nanomaterials in the hydrogel network, reducing their mechanical properties and treatment efficiency. Here, we demonstrate a promising approach of co-engineering nanomaterials and interfacial crosslinking to expand the materials construction and biomedical applications of NC hydrogels in SDT. In this work, mesoporous silica-coated titanium dioxide nanoparticles with thiolated surface functionalization (TiO₂@MS-SH) are utilized as crosslinkers to react with norbornene-functionalized dextran (Nor-Dex) through ultrasound-triggered thiol-norbornene reactions, forming TiO₂@MS-SH/Nor-Dex NC hydrogels. The TiO₂@MS-SH nanoparticles act not only as multivalent crosslinkers to improve the mechanical properties of hydrogels under ultrasound irradiation but also as reactive oxygen species (ROS) generators to allow the use of TiO₂@MS-SH/Nor-Dex NC hydrogels in SDT applications. Particularly, the TiO₂@MS-SH/Nor-Dex NC hydrogels present tailorable microstructures, properties, and sonodynamic killing of bacteria through the modulation of the ultrasound frequency. Taken together, a versatile TiO₂-based NC hydrogel platform prepared under ultrasonic interfacial crosslinking reactions is developed for advancing the applications in SDT.

Putative inactivation mechanism and germicidal efficacy of induced electric field against Staphylococcus aureus

Induced electric field (IEF), as an alternative non-conventional processing technique, is utilized to sterilize liquid foods. In this study, the survival and sublethal injury of S. aureus under IEF were investigated in 0.85% normal saline, and the inactivation mechanism of IEF was expounded. The plate count results showed that the sublethal injury rates remained above 90% after IEF treatment for more than 8.4 s, and 7.1 log CFU/mL of S. aureus was completely inactivated after 14 s IEF treatment. Scanning electron microscopy and transmission electron microscope images showed that IEF caused the destruction of cell membrane and internal substructure, and the damage to intracellular substructure was more severe. Altered membrane integrity or permeability was demonstrated through flow cytometry and confocal laser scanning microscope analysis, and the different damage to cells was quantified by propidium iodide & 5-carboxy fluorescein diacetate single and double staining. In addition, IEF treatment also decreased the membrane potential and esterase activity of S. aureus cells. Putative inactivation mechanism of IEF against S. aureus is a complex process, and its apoptosis is the result of the combination of several factors, which provide a basis for understanding the inactivation mechanism of IEF.

Ultrasound Technology as Inactivation Method for Foodborne Pathogens: A Review

An efficient microbiological decontamination protocol is required to guarantee safe food products for the final consumer to avoid foodborne illnesses. Ultrasound and non-thermal technology combinations represent innovative methods adopted by the food industry for food preservation and safety. Ultrasound power is commonly used with a frequency between 20 and 100 kHz to obtain an “exploit cavitation effect”. Microbial inactivation via ultrasound derives from cell wall damage, the oxidation of intracellular amino acids and DNA changing material. As an inactivation method, it is evaluated alone and combined with other non-thermal technologies. The evidence shows that ultrasound is an important green technology that has a good decontamination effect and can improve the shelf-life of products. This review aims to describe the applicability of ultrasound in the food industry focusing on microbiological decontamination, reducing bacterial alterations caused by food spoilage strains and relative foodborne intoxication/infection.

Graphene-Based Coating to Mitigate Biofilm Development in Marine Environments

Due to its several economic and ecological consequences, biofouling is a widely recognized concern in the marine sector. The search for non-biocide-release antifouling coatings has been on the rise, with carbon-nanocoated surfaces showing promising activity. This work aimed to study the impact of pristine graphene nanoplatelets (GNP) on biofilm development through the representative marine bacteria Cobetia marina and to investigate the antibacterial mechanisms of action of this material. For this purpose, a flow cytometric analysis was performed and a GNP/polydimethylsiloxane (PDMS) surface containing 5 wt% GNP (G5/PDMS) was produced, characterized, and assessed regarding its biofilm mitigation potential over 42 days in controlled hydrodynamic conditions that mimic marine environments. Flow cytometry revealed membrane damage, greater metabolic activity, and endogenous reactive oxygen species (ROS) production by C. marina when exposed to GNP 5% (w/v) for 24 h. In addition, C. marina biofilms formed on G5/PDMS showed consistently lower cell count and thickness (up to 43% reductions) than PDMS. Biofilm architecture analysis indicated that mature biofilms developed on the graphene-based surface had fewer empty spaces (34% reduction) and reduced biovolume (25% reduction) compared to PDMS. Overall, the GNP-based surface inhibited C. marina biofilm development, showing promising potential as a marine antifouling coating.

Quantitative proteomic analysis provides insight into the survival mechanism of Salmonella typhimurium under high-intensity ultrasound treatment

The survival mechanism of Salmonella treated with high-intensity ultrasound (HIU) should be explored to further enhance the bactericidal efficacy of HIU. In this study, culturable Salmonella was reduced by applying HIU. Electron microscope imaging revealed that HIU caused the disintegration of cell structure and leakage of intracellular substances. For the Salmonella after the HIU treatment, key enzymes of the tricarboxylic acid [TCA] cycle were significantly downregulated, which led to a reduced ATP content (45.25%-75.00%), although ATPase activity was augmented by 33.82%-60.64% in the Salmonella. Accordingly, surviving Salmonella could have tolerated the stress of HIU by upregulating their environmental sensing (two-component system), chemotaxis (bacterial chemotaxis), substance uptake (ABC transporter), and ATP production (oxidative phosphorylation). Therefore, synergistically blocking the ATP production, signal transduction, or substance intake of Salmonella offer promising potential strategies to improve the bactericidal effect of HIU in industrial food processing.

Comparison of Sputum Treated with Power Ultrasound and Routine NALC-NaOH Methods for Mycobacterial Culture: A Prospective Study

Mycobacterial culture remains the gold standard for the diagnosis of active tuberculosis. However, an appropriate digestion and decontamination method is essential for the effective recovery of tubercle bacilli in culture. The study was designed to compare the efficacy of sputum treated with power ultrasound (PU) and routine NALC-NaOH methods for mycobacterial culture from clinically suspected cases of pulmonary tuberculosis. To evaluate the PU and routine NALC-NaOH methods, sputum specimens (n = 597) were studied (culturing on MGIT 960), and the performances were compared. Of the 597 samples, 89 (14.91%) sputum samples treated with the NaOH-NALC method were mycobacterial culture positive, including Mycobacterium tuberculosis (M.TB; n = 77, 12.90%) and nontuberculous mycobacteria (NTM; n = 12, 2.01%). One hundred and ten (18.43%) sputum samples treated with the PU method were culture positive, including M.TB (n = 87, 14.57%) and NTM (n = 23, 3.85%). The PU method detected 10 additional cases of M.TB and 11 additional cases of NTM when compared to the NALC-NaOH method. Statistical analysis showed that a significant difference was found in the culture-positive ratio of M.TB and NTM between the two method groups (p < 0.05). Compared with that of the NALC-NaOH method (8.04%), sputum treated with PU method (4.86%) had a significantly lower contamination rate (p < 0.05). In conclusion, our data indicate that, compared with the NALC-NaOH method, the PU method is a rapid and effective approach for mycobacterial culture when detecting active TB. However, its accurate mechanism has not been well addressed, and further investigation is still required.

Alternative methods for cleaning membranes in water and wastewater treatment

Membrane fouling is caused by foulant deposition or adsorption through physical or chemical interactions on the membrane surface, causing the reduction of flux through the membrane. The main drawbacks of chemical agents used for cleaning are cost, damage caused on the membrane, and waste stream making the process unattractive. Alternative, methods such as ultrasound, enzymatic process, and osmotic backwashing were explored for membrane cleaning. Among all mentioned methods, micronanobubbles have been reported as a promising and emergent method for membrane surface cleaning; unfortunately, the information is limited, but preliminary studies have shown it as an efficient, cheap, and environmentally friendly technique. Other methods like electrically and vibratory-enhanced membrane cleaning also could be interesting but currently are unexplored and information is limited. PRACTITIONER POINTS: Chemical cleaning is an efficient option; however, from an environmental point of view, it is not attractive, and high concentrations could cause damage to the membrane. Micronanobubbles are an emergent and suitable technology for membrane and surface cleaning. Membrane modification and functionalization avoid membrane fast fouling, and the cleaning process is easier, but the manufacture cost could be expensive.

Bacteriostatic effects of high-intensity ultrasonic treatment on Bacillus subtilis vegetative cells

The bacteriostatic effects of high-intensity ultrasonic treatment (HIU) on Bacillus subtilis vegetative cells were evaluated, and the related mechanisms were explored using quantitative proteomics. The bacteriostatic effect of HIU on B. subtilis was proportional to the ultrasound treatment time and power, and the number of cultivable B. subtilis cells was decreased by approximately one log (at 270 W for 15 min) or half log (at 90 W for 25 min or 360 W for 5 min). Scanning electron microscopy images and gel electrophoresis results showed that HIU caused the destruction of the cell structure and intracellular protein leakage. In addition, HIU treatment at 270 W for 15 min resulted in the greatest decrease (84.22%) in intracellular adenosine triphosphate (ATP) content. The quantitative proteomic analysis showed that B. subtilis resisted the stress of HIU treatment by regulating the key proteins in physiological activities related to membrane transport (ATP-binding cassette [ABC] transporter), signal transduction (the two-component system), and energy metabolism (the tricarboxylic acid [TCA] cycle). HIU-induced physical damage, stress, and metabolic disorders were the main causes of the bacteriostatic effects on B. subtilis. These findings provide a foundation for the subsequent optimization and potential applications of HIU inactivation of B. subtilis.

Exosomal microRNAs from mesenchymal stem/stromal cells: Biology and applications in neuroprotection

Mesenchymal stem/stromal cells (MSCs) are extensively studied as cell-therapy agents for neurological diseases. Recent studies consider exosomes secreted by MSCs as important mediators for MSCs’ neuroprotective functions. Exosomes transfer functional molecules including proteins, lipids, metabolites, DNAs, and coding and non-coding RNAs from MSCs to their target cells. Emerging evidence shows that exosomal microRNAs (miRNAs) play a key role in the neuroprotective properties of these exosomes by targeting several genes and regulating various biological processes. Multiple exosomal miRNAs have been identified to have neuroprotective effects by promoting neurogenesis, neurite remodeling and survival, and neuroplasticity. Thus, exosomal miRNAs have significant therapeutic potential for neurological disorders such as stroke, traumatic brain injury, and neuroinflammatory or neurodegenerative diseases and disorders. This review discusses the neuroprotective effects of selected miRNAs (miR-21, miR-17-92, miR-133, miR-138, miR-124, miR-30, miR146a, and miR-29b) and explores their mechanisms of action and applications for the treatment of various neurological disease and disorders. It also provides an overview of state-of-the-art bioengineering approaches for isolating exosomes, optimizing their yield and manipulating the miRNA content of their cargo to improve their therapeutic potential.

Antibacterial mechanism of ultrasound against Escherichia coli: Alterations in membrane microstructures and properties

This study was aimed at providing new insights on the response of bacterial cell membranes to ultrasound exposure. Escherichia coli (E. coli) O157:H7 cells were exposed to different ultrasound treatments (power intensities of 64, 191, 372, and 573 W/cm², frequency of 20 kHz, pulsed mode of 2 sec: 2 sec) and the dynamic changes in cell viability within 27 min were assessed. With an increase in ultrasonic intensity and prolonged duration, a 0.76-3.52 log CFU/mL reduction in E. coli populations was attained. The alterations in the sensitivity of ultrasound-treated cells to antimicrobial compounds were evaluated by exposure to thyme essential oil nanoemulsion (TEON). The treatment reduced the E. coli population by 2.16-7.10 log CFU/mL, indicating the effects of ultrasonic field on facilitating the antibacterial efficacy of TEON. Ultrasonic-treated E. coli cells also displayed remarkable morphological and ultrastructural damages with destroyed membrane integrity and misshaped cell structures, which was observed by electron microscopy analysis. Significant increase in outer and inner membrane permeability, along with the cytoplasmic leakage and membrane depolarization were assessed utilizing spectrophotometry. For the first time, significant reduction in the membrane fluidity in response to ultrasound exposure were investigated. Additional efforts in exploring the effect of ultrasonic field on some bacterial membrane compositions were performed with infrared spectroscopy. In this study, multiple lines of evidence effectively served to elucidate the alterations on cellular membrane structure and property during exposure to sonication that could extend our understanding of the antimicrobial molecular mechanisms of ultrasound.

Challenges of antibiotic resistance biofilms and potential combating strategies: a review

In this modern era, medicine is facing many alarming challenges. Among different challenges, antibiotics are gaining importance. Recent years have seen unprecedented increase in knowledge and understanding of various factors that are root cause of the spread and development of resistance in microbes against antibiotics. The infection results in the formation of microbial colonies which are termed as biofilms. However, it has been found that a multiple factors contribute in the formation of antimicrobial resistance. Due to higher dose of Minimum Bactericidal Concentration (MBC) as well as of Minimum Inhibitory Concentration (MIC), a large batch of antibiotics available today are of no use as they are ineffective against infections. Therefore, to control infections, there is dire need to adopt alternative treatment for biofilm infection other than antibiotics. This review highlights the latest techniques that are being used to cure the menace of biofilm infections. A wide range of mechanisms has been examined with particular attention towards avenues which can be proved fruitful in the treatment of biofilms. Besides, newer strategies, i.e., matrix centered are also discussed as alternative therapeutic techniques including modulating microbial metabolism, matrix degrading enzyme, photodynamic therapy, natural compounds quorum sensing and nanotechnology which are being used to disrupt extra polymeric substances (EPS) matrix of desired bacterial biofilms.

Cumulative damage by nonthermal plasma (NTP) exceeds the defense barrier of multiple antibiotic-resistant Staphylococcus aureus: a key to achieve complete inactivation

Objectives

The aim of this study was to provide a comprehensive understanding of the nonthermal plasma (NTP)-induced inactivated behaviors on a multiple antibiotic–resistant (MAR) Staphylococcus aureus (S. aureus).

Materials and Methods

A dielectric barrier discharge (DBD) NTP system was employed for the inactivation of a MAR S. aureus under various applied powers of 35, 45, and 55 W, and gas distances of 4, 6, and 8 mm. The inactivation kinetics of S. aureus were estimated with linear and nonlinear predictive models. In addition, degradation of carotenoid pigment, peroxidation of fatty acids, oxidation of nucleic acids and proteins, and alteration in gene expression were analyzed after NTP treatment.

Results and Discussion

The computationally simulated results indicated that the densities of various reactive species increased with enhanced applied powers and decreased discharge distances. These species were further transformed into reactive oxidative and nitrogen species in the gas–liquid interphase and liquid phase. The oxidative and nitrosative stress of NTP resulted in severe damage to cellular components and the morphological structure of S. aureus. On the other hand, the plasma reactive species could also induce the sublethal injury of S. aureus through upregulating the general stress response, antioxidative and antinitrosative defensive systems. Once the cumulative damages overrode the stress tolerance of S. aureus, the completed cell death was finally achieved by NTP.

Conclusions

This work infers the possible risk of inducing the repair and resistant capacity of pathogens when the applied NTP parameters are inappropriate, which helps the optimization of NTP process to achieve sufficient inactivation.

Transcriptomic analysis reveal differential gene expressions of Escherichia coli O157:H7 under ultrasonic stress

In order to uncover the molecular regulatory mechanisms underlying the phenotypes, the overall regulation of genes at the transcription level in Escherichia coli O157:H7 after ultrasonic stimulation were investigated by RNA-sequencing and real-time quantitative polymerase chain reaction. The results revealed that differential expressions of 1217 genes were significant when exposed at 6.67 W/mL power ultrasonic density for 25 min, including 621 up-regulated and 596 down-regulated genes. Gene transcription related to a series of crucial biomolecular processes were influenced by the ultrasonic stimulation, including carbohydrate metabolism, energy metabolism, membrane transport, signal transduction, transcription and translation. The most enriched pathways were further analyzed in each category. Specifically, genes encoded citrate cycle were down-regulated in E. coli O157:H7, indicating the capacity to decompose carbohydrate and produce energy were decreased under ultrasonic stress. Accompanied with energy loss, the membrane function was affected by the ultrasonic stimulation since the majority of genes encoded ATP-binding cassette transporters were down-regulated. Besides, the autoinducer 2-mediated signal transduction was also inhibited. The interesting thing, however, the protein translation processing was benefited under ultrasonic field. This phenomenon might due to the desperate need of stress response proteins when the bacteria were under stress. We believed that the sonomechanical and sonochemical effects generated by acoustic cavitation were responsible for those gene expression changes.

Degradation of antibiotic resistance contaminants in wastewater by atmospheric cold plasma: kinetics and mechanisms

This work employed the atmospheric cold plasma technology to efficiently control the antibiotic resistance contaminants in the wastewater effluent. We found that the plasma inactivated the antibiotic-resistant Escherichia coli through multiple damages on the cell membranes and intracellular components (enzymes and DNA). Plasma treatment at an influence of 0.71 kJ/cm² resulted in a more than 3 log₁₀ CFU/ml reduction (>99.999%) of E. coli in an actual wastewater system. We further estimated the effect of plasma on the ampicillin (bla_TEM ) and tetracycline (tet) resistance genes. The results demonstrated that an applied plasma dose of 1.06 kJ/cm² could significantly (P < .05) eliminate the extracellular (e-) bla_TEM and tet genes by 3.26 and 3.14 log₁₀ copies/ml, respectively. Higher plasma intensity was required for the efficient reduction of intracellular (i-)antibiotic resistance genes (ARGs) than extracellular (e-)ARGs due to the shielding effect of the outer envelopes or intracellular components. The inactivation of E. coli and the degradation of e- and i-ARGs can be well described by the Weibull models. The results here provide the evidence for the potential of the plasma technology as a water/wastewater treatment technology.

The potential advantages of using a poly(HPMA) brush in urinary catheters: effects on biofilm cells and architecture

Infections related to bacterial colonization of medical devices are a growing concern given the socio-economical impacts in healthcare systems. Colonization of a device surface with bacteria usually triggers the development of a biofilm, which is more difficult to eradicate than free-floating or adhered bacteria and can act as a reservoir for subsequent infections. Biofilms often harbor Viable but nonculturable (VBNC) cells that are likely to be more resistant to antibiotic treatment and that can become active in more favorable conditions causing infection. Biofilm formation is dependent on different factors, chiefly the properties of the surface and of the surrounding medium, and the hydrodynamic conditions. In this work, the antifouling performance of a poly[N-(2-hydroxypropyl) methacrylamide] (poly(HPMA)) brush was evaluated in vitro in conditions that mimic a urinary catheter using Escherichia coli as a model organism. The results obtained with the brush were compared to those obtained with two control surfaces, polydimethylsiloxane (PDMS) (the most common material for catheters) and glass. A decrease in initial adhesion and surface coverage was observed on the brush. This antifouling behavior was maintained during biofilm maturation and even in a simulated post-bladder infection period when the reduction in total cell number reached 87 %. Biofilms were shown to adapt their architecture during that period and VBNC cells adsorbed weakly on the brushes and were completely washed away. Taken together, these results suggest that the use of the poly(HPMA) brush in urinary tract devices such as catheters and stents may reduce biofilm formation and possibly render the formed biofilms more susceptible to antibiotic treatment and with reduced infectivity potential.

Nonthermal Plasma Induces the Viable-but-Nonculturable State in Staphylococcus aureus via Metabolic Suppression and the Oxidative Stress Response

As a novel nonthermal technology, nonthermal plasma (NTP) has attracted a lot of attention. However, it could induce microorganisms into a viable but nonculturable (VBNC) state, posing a potential risk to food safety and public health. In this study, the molecular mechanisms of VBNC Staphylococcus aureus induced by NTP were investigated. With the use of a propidium monoazide quantitative PCR (PMA-qPCR) technique combined with a plate count method, we confirmed that 8.1 to 24.3 kJ NTP induced S. aureus into a VBNC state at a level of 7.4 to 7.6 log10 CFU/ml. The transcriptomic analysis was conducted and revealed that most energy-dependent physiological activities (e.g., metabolism) were arrested in VBNC S. aureus, while the oxidative stress response-related genes (katA, dps, msrB, msrA, and trxA) were significantly upregulated. In addition, this study showed that the ATP depletion by carbonyl cyanide m-chlorophenyl hydrazone (CCCP) pretreatment could accelerate the formation of VBNC S. aureus The NTP-generated oxidative stress triggers the staphylococcal oxidative stress response, which consumes part of cellular energy (e.g., ATP). The energy allocation is therefore changed, and the energy assigned for other energy-dependent physiological activities (cell growth and division, etc.) is reduced, subsequently forcing S. aureus into a VBNC state. Therefore, the alterations of energy allocation should be some of the major contributors to the induction of VBNC S. aureus with NTP exposure. This study provides valuable knowledge for controlling the formation of VBNC S. aureus during NTP treatment.IMPORTANCE In recent years, nonthermal plasma (NTP) technology has received a lot of attention as a promising alternative to thermal pasteurization in the food industry. However, little is known about the microbial stress response toward NTP, which could be a potential risk to food safety and impede the development of NTP. A viable but nonculturable (VBNC) state is one of the most common survival strategies employed by microorganisms against external stress. This study investigated the mechanisms of the formation of VBNC Staphylococcus aureus by NTP in a more comprehensive and systematic aspect than had been done before. Our work confirmed that the NTP-generated oxidative stress induced changes in energy allocation as a driving force for the formation of VBNC S. aureus This study could provide better knowledge for controlling the occurrence of VBNC S. aureus induced by NTP, which could lead to more rational design and ensure the development of safe foods.

Comparison of metabolic response between the planktonic and air-dried Escherichia coli to electrolysed water combined with ultrasound by 1H NMR spectroscopy

The antimicrobial effects of electrolysed water and ultrasound have been well reported; however, little attention was paid to their effects on the metabolite changes of bacteria in different states. In this study, the metabolomic variations of Escherichia coli ATCC 25922 in planktonic and adherent state (air-dried on stainless steel coupons) after the combination treatment of low-concentration acidic electrolysed water (AEW, free available chlorine (FAC): 4 mg/L) and ultrasound were characterised, by conducting multivariate data analysis based on nuclear magnetic resonance (NMR) spectroscopy. Overall, 43 metabolites were identified in two states of E. coli, including a wide range of amino acids, organic acids, nucleotides and their derivatives. The quantification of whole-cell metabolism in planktonic and air-dried cultures was quite different: air-dried E. coli exhibited more resistance to ultrasound and AEW treatments due to initiating a protective response against oxidative and acid stresses, which was not observed in planktonic E. coli, whose levels of all identified metabolites were decreased significantly after the combined treatment. Further pathway analysis revealed that alanine, aspartate and glutamate metabolism, glycolysis, pyruvate metabolism and tricarboxylic acid (TCA) cycle were changed significantly in planktonic culture, but to a less extent in air-dried culture, in which some shifts in glutamate decarboxylase (GAD) system and some shunts like mixed acid fermentation and pentose phosphate pathway were observed for maintaining metabolic balance. These findings suggest that NMR-based metabolomics strategy is promising in identifying different metabolic shifts in different states of bacteria. They also provide some guidance for food equipment sanitisation, especially for organic food processing.