Effects of ozone on membrane permeability and ultrastructure in Pseudomonas aeruginosa

Activity of biogenic silver nanoparticles in planktonic and biofilm-associated Corynebacterium pseudotuberculosis

Corynebacterium pseudotuberculosis is a gram-positive bacterium and is the etiologic agent of caseous lymphadenitis (CL) in small ruminants. This disease is characterized by the development of encapsulated granulomas in visceral and superficial lymph nodes, and its clinical treatment is refractory to antibiotic therapy. An important virulence factor of the Corynebacterium genus is the ability to produce biofilm; however, little is known about the characteristics of the biofilm produced by C. pseudotuberculosis and its resistance to antimicrobials. Silver nanoparticles (AgNPs) are considered as promising antimicrobial agents, and are known to have several advantages, such as a broad-spectrum activity, low resistance induction potential, and antibiofilm activity. Therefore, we evaluate herein the activity of AgNPs in C. pseudotuberculosis, through the determination of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), antibiofilm activity, and visualization of AgNP-treated and AgNP-untreated biofilm through scanning electron microscopy. The AgNPs were able to completely inhibit bacterial growth and inactivate C. pseudotuberculosis at concentrations ranging from 0.08 to 0.312 mg/mL. The AgNPs reduced the formation of biofilm in reference strains and clinical isolates of C. pseudotuberculosis, with interference values greater than 80% at a concentration of 4 mg/mL, controlling the change between the planktonic and biofilm-associated forms, and preventing fixation and colonization. Scanning electron microscopy images showed a significant disruptive activity of AgNP on the consolidated biofilms. The results of this study demonstrate the potential of AgNPs as an effective therapeutic agent against CL.

Antibacterial Mechanisms and Antivirulence Activities of Oridonin against Pathogenic Aeromonas hydrophila AS 1.1801

Aeromonas hydrophila, a Gram-negative bacterium widely found in freshwater environments, acts as a common conditional pathogen affecting humans, livestock, and aquatic animals. In this study, the impact of oridonin, an ent-kaurane diterpenoid compound derived from Rabdosia rubescens, on the virulence factors of A. hydrophila AS 1.1801 and its antibacterial mechanism was elucidated. The minimum inhibitory concentration (MIC) of oridonin against A. hydrophila AS 1.1801 was 100 μg/mL. Oridonin at inhibitory concentrations could significantly increase the electrical conductivity in the supernatant and escalate nucleic acid leakage (p < 0.01). This effect was concomitant with observed distortions in bacterial cells, the formation of cytoplasmic cavities, cellular damage, and pronounced inhibition of protein and nucleic acid synthesis. Additionally, oridonin at inhibitory levels exhibited a noteworthy suppressive impact on A. hydrophila AS 1.1801 across biofilm formation, motility, hemolytic activity, lipase activity, and protease activity (p < 0.05), demonstrating a dose-dependent enhancement. qRT-PCR analysis showed that the gene expression of luxR, qseB and omp were significantly downregulated after oridonin treatment in A. hydrophila AS 1.1801 (p < 0.05). Our results indicated that oridonin possessed significant antibacterial and anti-virulence effects on A. hydrophila AS 1.1801.

Use of Ozonized Water in the Prevention of Surgical Site Infection in Children Undergoing Cardiovascular Surgery

INTRODUCTION

Since the reduction of healthcare-associated infections has been a focus for quality patient care, this study aimed to evaluate the surgical site infection rate of children who underwent cardiovascular surgery after implementation of ozonized water system for hand and body hygiene allied to previously implemented preventive measures.

METHODS

Two uniformly comparable groups of pediatric patients underwent cardiovascular surgery. Group A (187) patients were operated prior to installation of ozonized water system (March 1 to August 31, 2019), and group B (214) patients were operated after installation of ozonized water system (October 1, 2019, to March 31, 2020). Ozonized water was used for professional hand hygiene and patient body hygiene.

RESULTS

There was statistical significance for surgical site infection reduction in group B (P=0.0289), with a relative risk of 0.560 (95% confidence interval = 0.298 to 0.920), inferring the risk of being diagnosed with surgical site infections in group B was 44% less than in group A. There was no statistical significance regarding mechanical ventilation time (P=0.1998) or mortality (P=0.4457).

CONCLUSION

Ozonized water for professional hand hygiene and patient body hygiene was an adjuvant combined with traditional preventive methods to reduce the risk of surgical site infection, although no impact on hospital stay or mortality was observed.

Peracetic acid disinfection induces antibiotic-resistant E. coli into VBNC state but ineffectively eliminates the transmission potential of ARGs

The occurrence of a viable but nonculturable (VBNC) state in antibiotic-resistant E. coli (AR E. coli) and inefficient degradation of their antibiotic resistance genes (ARGs) may cause potential health risks during disinfection. Peracetic acid (PAA) is an alternative disinfectant for replacing chlorine-based oxidants in wastewater treatment, and the potential of PAA to induce a VBNC state in AR E. coli and to remove the transformation functionality of ARGs were investigated for the first time. Results show that PAA exhibits excellent performance in inactivating AR E. coli (over 7.0-logs) and persistently inhibiting its regeneration. After PAA disinfection, insignificant changes in the ratio of living to dead cells (∼4%) and the level of cell metabolism, indicating that AR E. coli were induced into VBNC states. Unexpectedly, PAA was found to induce AR E. coli into VBNC state by destroying the proteins containing reactive amino acids at thiol, thioether and imidazole groups, rather than the result of membrane damage, oxidative stress, lipid destruction and DNA disruption in the conventional disinfection processes. Moreover, the result of poor reactivity between PAA and plasmid strands and bases confirmed that PAA hardly reduced the abundance of ARGs and damaged the plasmid's integrity. Transformation assays and real environment validation indicated that PAA-treated AR E. coli could release large abundance of naked ARGs with high-efficiency transformation functionality (∼5.4 × 10-4 - ∼8.3 × 10-6) into the environment. This study has significant environmental implications for assessing the transmission of antimicrobial resistance during PAA disinfection.

Chitosan decorated essential oil nanoemulsions for enhanced antibacterial activity using a microfluidic device and response surface methodology

In this work, the antibacterial activity of Satureja Khuzestanica essential oil nanoemulsions improved by employing chitosan (ch/SKEO NE) against E. coli bacterium. The optimum ch/SKEO NE with mean droplet size of 68 nm was attained at 1.97, 1.23, and 0.10%w/w of surfactant, essential oil and chitosan, using Response Surface Methodology (RSM). Applying microfluidic platform, the ch/SKEO NE resulted in improved antibacterial activity owing to the modification of surface properties. The nanoemulsion samples showed a significant rupturing effect on the E. coli bacterial cell membrane which resulted in a rapid release of cellular contents. This action was remarkably intensified by executing microfluidic chip in parallel to the conventional method. Having treated the bacteria in the microfluidic chip for 5 min with a 8 μg/mL concentration of ch/SKEO NE, the bacterial integrity disrupted quickly, and the activity was totally lost in a 10-min period at 37 μg/mL, while it took 5 h for a complete inhibition in the conventional method using the same concentration of ch/SKEO NE. It can be concluded that nanoemulsification of EOs using chitosan coating can intensify the interaction of nanodroplets with the bacterial membrane, especially within the microfluidic chips which provides high contact surface area.

Interaction of a natural compound nanoemulsion with Gram negative and Gram positive bacterial membrane; a mechanism based study using a microfluidic chip and DESI technique

The antibacterial activity of a nanoemulsion prepared from Satureja Khusitanica essential oil against a Gram-negative (Escherichia coli) and a Gram-positive (Bacillus atrophaeus) bacteria evaluated using microfluidic and conventional techniques. The effect of different residence time and concentrations on the antibacterial activity of nanoemulsion was studied by measuring the release of protein, nucleic acids, potassium, and also recording the MIC, MBC and time killing assays. Remarkable intensification was observed by employing microfluidic chip regarding a high-contact surface area between nanodroplets and bacterial membrane. The MIC and MBC values for E. coli and B. atrophaeus in conventional method were 400 and 1600 µg mL^-1, respectively, whereas these values reduced to 11 to 50 µg mL^-1 using microfluidic system. B. atrophaeus seemed to be more resistant than E. coli to the nanoemulsion treatment, perhaps due to different cell wall structures. Bacterial cell wall changes were examined using a desorption electrospray ionization (DESI) technique. It was found that the structural changes were more imminent in Gram negative E. coli by detecting a number of released lipids including phosphatidyl glycerol and phosphatidyl ethanolamines. The DESI spectra of B. atrophaeus revealed no M/Z related lipid release. These findings may help providing novel nano based natural antibacterials.

Effectiveness of ozone generated by a dielectric barrier discharge plasma reactor against multidrug-resistant pathogens and Clostridioides difficile spores

The contaminated healthcare environment plays an important role in the spread of multidrug-resistant organisms (MDROs) and Clostridioides difficile. This study aimed to evaluate the antimicrobial effects of ozone generated by a dielectric barrier discharge (DBD) plasma reactor on various materials that were contaminated by vancomycin-resistant Enterococcus faecium (VRE), carbapenem-resistant Klebsiella pneumoniae (CRE), carbapenem-resistant Pseudomonas aeruginosa (CRPA), carbapenem-resistant Acinetobacter baumannii (CRAB) and C. difficile spores. Various materials contaminated by VRE, CRE, CRPA, CRAB and C. difficile spores were treated with different ozone concentrations and exposure times. Atomic force microscopy (AFM) demonstrated bacterial surface modifications following ozone treatment. When an ozone dosage of 500 ppm for 15 min was applied to VRE and CRAB, about 2 or more log₁₀ reduction was observed in stainless steel, fabric and wood, and a 1–2 log₁₀ reduction in glass and plastic. Spores of C. difficile were more resistant to ozone than were all other tested organisms. On AFM, the bacterial cells, following ozone treatment, were swollen and distorted. The ozone generated by the DBD plasma reactor provided a simple and valuable decontamination tool for the MDROs and C. difficile spores, which are known as common pathogens in healthcare-associated infections.

SARS-CoV-2 pseudotyped virus persists on the surface of multiple produce but can be inactivated with gaseous ozone

Due to the immense societal and economic impact that the COVID-19 pandemic has caused, limiting the spread of SARS-CoV-2 is one of the most important priorities at this time. The global interconnectedness of the food industry makes it one of the biggest concerns for SARS-CoV-2 outbreaks. Although fomites are currently considered a low-risk route of transmission for SARS-CoV-2, new variants of the virus can potentially alter the transmission dynamics. In this study, we compared the survival rate of pseudotyped SARS-CoV-2 on plastic with some commonly used food samples (i.e., apple, strawberry, grapes, tomato, cucumber, lettuce, parsley, Brazil nut, almond, cashew, and hazelnut). The porosity level and the chemical composition of different food products affect the virus's stability and infectivity. Our results showed that tomato, cucumber, and apple offer a higher survival rate for the pseudotyped viruses. Next, we explored the effectiveness of ozone in deactivating the SARS-CoV-2 pseudotyped virus on the surface of tomato, cucumber, and apple. We found that the virus was effectively inactivated after being exposed to 15 ppm of ozone for 1 h under ambient conditions. SEM imaging revealed that while ozone exposure altered the wax layer on the surface of produce, it did not seem to damage the cells and their biological structures. The results of our study indicate that ozonated air can likely provide a convenient method of effectively disinfecting bulk food shipments that may harbour the SARS-CoV-2 virus.

Potent Activity of a High Concentration of Chemical Ozone against Antibiotic-Resistant Bacteria

BACKGROUND

Health care-associated infections (HAIs) are a significant public health problem worldwide, favoring multidrug-resistant (MDR) microorganisms. The SARS-CoV-2 infection was negatively associated with the increase in antimicrobial resistance, and the ESKAPE group had the most significant impact on HAIs. The study evaluated the bactericidal effect of a high concentration of O3 gas on some reference and ESKAPE bacteria.

MATERIAL AND METHODS

Four standard strains and four clinical or environmental MDR strains were exposed to elevated ozone doses at different concentrations and times. Bacterial inactivation (growth and cultivability) was investigated using colony counts and resazurin as metabolic indicators. Scanning electron microscopy (SEM) was performed.

RESULTS

The culture exposure to a high level of O3 inhibited the growth of all bacterial strains tested with a statistically significant reduction in colony count compared to the control group. The cell viability of S. aureus (MRSA) (99.6%) and P. aeruginosa (XDR) (29.2%) was reduced considerably, and SEM showed damage to bacteria after O3 treatment Conclusion: The impact of HAIs can be easily dampened by the widespread use of ozone in ICUs. This product usually degrades into molecular oxygen and has a low toxicity compared to other sanitization products. However, high doses of ozone were able to interfere with the growth of all strains studied, evidencing that ozone-based decontamination approaches may represent the future of hospital cleaning methods.

Impact of electrolyte solution on electrochemical oxidation treatment of Escherichia coli K-12 by boron-doped diamond electrodes

We studied the disinfection efficacy of boron-doped electrodes on Escherichia coli-contaminated water-based solutions in three different electrolytes, physiological solution (NaCl), phosphate buffer (PB), and phosphate buffer saline (PBS). The effect of the electrochemical oxidation treatment on the bacteria viability was studied by drop and spread plate cultivation methods, and supported by optical density measurements. We have found that bacterial suspensions in NaCl and PBS underwent a total inactivation of all viable bacteria within 10 min of the electrochemical treatment. By contrast, experiments performed in the PB showed a relatively minor decrease of viability by two orders of magnitude after two hours of the treatment, which is almost comparable with the untreated control. The enhanced bacterial inactivation was assigned to reactive chlorine species (RCS), capable of penetrating the bacterial cytoplasmic membrane and killing bacteria from within.

Effectiveness of Low-Dose Continuous Gaseous Ozone in Controlling Listeria innocua on Red Delicious Apples During 9-Month Commercial Cold Storage

This study aimed to investigate the effects of low-dose continuous ozone gas in controlling Listeria innocua and quality attributes and disorders of Red Delicious apples during long-term commercial cold storage. Red Delicious apples were inoculated with a three-strain L. innocua cocktail at ∼6.2 log10 CFU/apple, treated with or without 1-methylcyclopropene, and then subjected to controlled atmosphere (CA) storage with or without continuous gaseous ozone in a commercial facility for 36 weeks. Uninoculated Red Delicious apples subjected to the above storage conditions were used for yeast/mold counts and quality attributes evaluation. The 36 weeks of refrigerated air (RA) or CA storage caused ∼2.2 log10 CFU/apple reduction of L. innocua. Ozone gas application caused an additional > 3 log10 CFU/apple reduction of L. innocua compared to RA and CA storage alone. During the 36-week CA storage, low-dose continuous gaseous ozone application significantly retarded the growth of yeast/mold, delayed apple firmness loss, and had no negative influence on ozone burn, lenticel decay, russet, CO2 damage, superficial scald, and soft scald of Red Delicious apples compared to CA-alone storage. In summary, the application of continuous low-dose gaseous ozone has the potential to control Listeria on Red Delicious apples without negatively influencing apple quality attributes.

Genomic Analysis and Stability Evaluation of the Phenol-Degrading Bacterium Acinetobacter sp. DW-1 During Water Treatment

Phenol is a toxic organic molecule that is widely detected in the natural environment, even in drinking water sources. Biological methods were considered to be a good tool for phenol removal, especially microbial immobilized technology. However, research on the “seed” bacteria along with microbial community analysis in oligotrophic environment such as drinking water system has not been addressed. In this study, Acinetobacter sp. DW-1 with high phenol degradation ability had been isolated from a drinking water biofilter was used as seeded bacteria to treat phenol micro-polluted drinking water source. Meanwhile, the whole genome of strain DW-1 was sequenced using nanopore technology. The genomic analysis suggests that Acinetobacter sp. DW-1 could utilize phenol via the β-ketoadipate pathway, including the catechol and protocatechuate branches. Subsequently, a bio-enhanced polyhedral hollow polypropylene sphere (BEPHPS) filter was constructed to investigate the stability of the seeded bacteria during the water treatment process. The denatured gradient gel electrophoresis (DGGE) profile and the quantification of phenol hydroxylase gene results indicate that when the BEPHPS filter was operated for 56 days, Acinetobacter sp. was still a persistent and competitive bacterium in the treatment group. In addition, 16S rRNA gene amplicon sequencing results indicate that Acinetobacter sp., as well as Pseudomonas sp., Nitrospira sp., Rubrivivax sp. were the predominant bacteria in the treatment group, which were different from that in the CK group. This study provides a better understanding of the mechanisms of phenol degradation by Acinetobacter sp. DW-1 at the gene level, and provides new insights into the stability of seeded bacteria and its effects on microbial ecology during drinking water treatment.

Ozonized Water in Microbial Control: Analysis of the Stability, In Vitro Biocidal Potential, and Cytotoxicity

O3 dissolved in water (or ozonized water) has been considered a potent antimicrobial agent, and this study aimed to test this through microbiological and in vitro assays. The stability of O3 was accessed following modifications of the physicochemical parameters of water, such as the temperature and pH, with or without buffering. Three concentrations of O3 (0.4, 0.6, and 0.8 ppm) dissolved in water were tested against different microorganisms, and an analysis of the cytotoxic effects was also conducted using the human ear fibroblast cell line (Hfib). Under the physicochemical conditions of 4 °C and pH 5, O3 remained the most stable and concentrated compared to pH 7 and water at 25 °C. Exposure to ozonized water resulted in high mortality rates for Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, and Candida albicans. Scanning electron micrograph images indicate that the effects on osmotic stability due to cell wall lysis might be one of the killing mechanisms of ozonized water. The biocidal agent was biocompatible and presented no cytotoxic effect against Hfib cells. Therefore, due to its cytocompatibility and biocidal action, ozonized water can be considered a viable alternative for microbial control, being possible, for example, its use in disinfection processes.

A quantitative analysis method to determine the amount of cellulose fibre in waste sludge

A novel quantitative analysis method for cellulose fibre was developed to understand its behaviour in biological wastewater treatment and waste sludge processes. The method developed in this study was designed using Pseudomonas aeruginosa to remove it by dissolving all the organic components except cellulose from the sludge due to needing the solubilisation of bacteria occupied almost of sludge matrix and quantifying the amount of remaining cellulose. The results of this study indicated that a combined treatment process that employed 2,000 U/L protease, 2 M hydrogen peroxide, and 2 mM potassium hydroxide after pre-treatment for floc dispersion with an ultrasonic treatment at 26 W for 1 min resulted in a solubilisation of 96% of P. aeruginosa without losing the cellulose fibre. When it was applied to the cellulose fibre added in the sludge from a municipal wastewater treatment facility, 99.5% of the cellulose fibre was recovered by using the high-speed centrifuge.

Ozone Exposure Induces Metabolic Disorders and NAD+ Depletion Through PARP1 Activation in Spinal Cord Neurons

Background and Objective: Ozone therapy has shown therapeutic efficacy in different disorders particularly low back pain (LBP). However, ozone therapy has been associated with toxic effects on the respiratory, endocrine, cardiovascular systems as well as nervous system because of its strong oxidizing capacity. Recent studies have reported possible associations between ozone exposure and metabolic disorders, but the findings are controversial and little is known on the mechanisms of action. This study aims to investigate the cytotoxic effects of ozone exposure and possible mechanism of action in the animal model.

Methods: Wistar neonate rats with the age of 24 h after birth were sacrificed by cervical dislocation under general anesthesia, then immersed in 75% alcohol and iodophor for 5 min, respectively. The spinal cord was isolated and cut to samples of ~1 mm³ and prepared for further experiments. The spinal cord neurons (SCNs) were exposed to ozone at different concentrations and then cultured in 96-well plates with glass bottom for 7 days. The cell viability, ATP levels and the NAD+ concentration were determined and compared between the different experimental groups and the control group.

Results: Analyses of the data by non-targeted liquid chromatography-mass spectrometry (LC-MS) analysis determined the metabolic disorder in SCNs following the ozone exposure. Moreover, our assessments showed that ozone exposure resulted in DNA damage, poly (ADP)-ribose polymerase-1 (PARP1) excessive activation, nicotinamide adenine dinucleotide (NAD+) depletion and decrease of ATP level in SCNs. The PARP1 inhibitor can inhibit the cytotoxic effect of ozone to SCNs without inhibiting the activation of AMP-activated protein kinase (AMPK). Our findings revealed that the cytotoxic effects of ozone to SCNs might be mediated by excessive PARP1 activation and subsequent NAD+ depletion. Moreover, using PARP1 inhibitor can protect SCNs from cytotoxic effects of ozone by preventing NAD+ depletion during ozone exposure.

Conclusion: Ozone exposure seems to induce metabolic disorders and NAD+ depletion through excessive PARP1 activation in SCNs.

Antibiofilm effect of ozonized physiological saline solution on peri-implant-related biofilm

BACKGROUND

Removal of dental plaque and local application of local chemical adjuncts, such as chlorhexidine (CHX), have been used to control and treat peri-implant disease. However, these methods can damage the surface properties of the implants or promote bacterial resistance. The application of ozone as an adjunctive treatment represents a new approach in the management of peri-implantitis. Thus, the purpose of this study was to evaluate the antimicrobial effect of ozonized physiological saline solution in different concentrations against oral biofilms developed on titanium surface.

METHODS

Single and multi-species biofilms of Porphyromonas gingivalis, Fusobacterium nucleatum, and Streptococcus oralis were formed on titanium specimens for 5 days in anaerobic conditions. Biofilms were treated with ozonized saline solution at different concentrations (25, 50, and 80 μg/NmL), for 30 seconds and 1 minute. CHX (0.12%) and saline solution (0.89% NaCl) were used as positive and negative controls, respectively. Bacterial viability was quantified by colony forming units (CFU mL^-1 ), and biofilm images were acquired by confocal laser scanning microscopy (CLSM). Data were analyzed by parametric test (ANOVA) with Tukey post-hoc test (P < 0.05).

RESULTS

Ozonized saline solution showed antibiofilm activity at a concentration of 80 μg/NmL for 30 seconds and 1 minute, reducing, mainly, Porphyromonas gingivalis viability, with 2.78 and 1.7 log₁₀ CFU mL^-1 of reduction in both single and multi-species biofilms, respectively, when compared to the control (saline), whereas CHX reduced 1.4 and 1.2 log₁₀ CFU mL^-1 .

CONCLUSION

Ozonized saline solution has antibiofilm activity, with better effect when applied for 1 minute at 80 μg/NmL, being a promising candidate therapy for the treatment of peri-implant diseases.

Dissemination prevention of antibiotic resistant and facultative pathogenic bacteria by ultrafiltration and ozone treatment at an urban wastewater treatment plant

Conventional wastewater treatment is not sufficient for the removal of hygienically relevant bacteria and achieves only limited reductions. This study focuses on the reduction efficiencies of two semi-industrial ultrafiltration units operating at a large scale municipal wastewater treatment plant. In total, 7 clinically relevant antibiotic resistance genes, together with 3 taxonomic gene markers targeting specific facultative pathogenic bacteria were analysed via qPCR analyses before and after advanced treatment. In parallel with membrane technologies, an ozone treatment (1 g ozone/g DOC) was performed for comparison of the different reduction efficiencies. Both ultrafiltration units showed increased reduction efficiencies for facultative pathogenic bacteria and antibiotic resistance genes of up to 6 log units, resulting mostly in a strong reduction of the bacterial targets. In comparison, the ozone treatment showed some reduction efficiency, but was less effective compared with ultrafiltration due to low ozone dosages frequently used for micro-pollutant removal at municipal wastewater treatment plants. Additionally, metagenome analyses demonstrated the accumulation of facultative pathogenic bacteria, antibiotic resistance genes, virulence factor genes, and metabolic gene targets in the back flush retentate of the membranes, which opens further questions about retentate fluid material handling at urban wastewater treatment plants.

Composition and Dynamics of Bacterial Communities in a Full-Scale Mineral Water Treatment Plant

The aim of this study was to gain insight into the bacterial composition and dynamics in a mineral water treatment system (MWTS). The bacterial community of a full-scale mineral water treatment plant in the Maofeng Mountain, South China, was studied using high-throughput sequencing combined with cultivation-based techniques in both the dry and wet season. Overall, adenosine tri-phosphate (ATP) concentration (6.47 × 10^-11 – 3.32 × 10^-8 M) and heterotrophic plate counts (HPC) (3 – 1.29 × 10³ CFU/mL) of water samples in the wet season were lower than those (ATP concentration 5.10 × 10^-11 – 6.96 × 10^-8 M, HPC 2 – 1.97 × 10³ CFU/mL) in the dry season throughout the whole MWTS. The microbial activity and biomass of water samples obviously changed along with treatment process. All 300 isolates obtained using cultivation-based techniques were distributed in 5 phyla, 7 classes, and 19 genera. Proteobacteria accounted for 55.7% (167) of the total isolates, among which predominant genus was Pseudomonas (19.3%). Illumina sequencing analysis of 16s rRNA genes revealed 15 bacterial phyla (relative abundance >0.1%) as being identified in all water samples. Among these, Proteobacteria constituted the dominant bacteria microbiota in all water samples. A large shift in the proportion of Bacteroidetes, Actinobacteria, and Firmicutes was obtained during the treatment process, with the proportion of Bacteroidetes, Actinobacteria decreasing sharply, whereas that of Firmicutes increased and predominated in the final water product. The core microbiome, which was still present in whole MWTS comprised several genera including Pseudomonas, Acinetobacter, Clostridium, and Mycobacterium, that contain species that are opportunistic pathogens, suggesting a potential threat for mineral water microbiology safety. This study is the first to investigate the bacterial community of a full-scale mineral water treatment plant in China. The results provided data regarding the bacteria composition and dynamics in an MWTS, which will contribute to the beneficial manipulation of the mineral water microbiome.

Ozone against Pseudomonas aeruginosa biofilms in contact lenses storage cases

Pseudomonas aeruginosa is associated with ocular infections such as keratitis. Multipurpose contact lens solutions can be used for washing, disinfection and storage of contact lenses, however, P. aeruginosa biofilm disinfection by this method is unsatisfactory. The present study aimed to investigate the effectiveness of ozonated water in reducing P. aeruginosa colony count. Lenses kept in storage cases were contaminated with P. aeruginosa and disinfected using ozonized water, chlorhexidine, ultrasound and multipurpose solutions. The multipurpose solutions and ultrasound methods reduced colony count from 1.17 to 1.63 log10 CFU/cm2 (92.93% to 97.31%), respectively, of P. aeruginosa biofilm cell viability when compared to the positive control. Both, ozonated water and chlorhexidine showed 7.42 log reduction in the number of viable cells of P. aeruginosa biofilm. As compared to chlorhexidine, ozonized water did not depose any known toxic residues, so that we recommend it as an alternative disinfectant solution for contact lenses storage cases.

Changes of Intracellular Porphyrin, Reactive Oxygen Species, and Fatty Acids Profiles During Inactivation of Methicillin-Resistant Staphylococcus aureus by Antimicrobial Blue Light

Antimicrobial blue light (aBL) has attracted increasing interest for its antimicrobial properties. However, the underlying bactericidal mechanism has not yet been verified. One hypothesis is that aBL causes the excitation of intracellular chromophores; leading to the generation of reactive oxygen species (ROS) and the resultant oxidization of various biomolecules. Thus, monitoring the levels of redox-sensitive intracellular biomolecules such as coproporphyrins, as well as singlet oxygen and various ROS may help to uncover the physiological changes induced by aBL and aid in establishing the underlying mechanism of action. Furthermore, the identification of novel targets of ROS, such as fatty acids, is of potential significance from a therapeutic perspective. In this study, we sought to investigate the molecular impact of aBL treatment on methicillin-resistant Staphylococcus aureus (MRSA). The results showed that aBL (5–80 J/cm²) exhibited a bactericidal effect on MRSA, and almost no bacteria survived when 80 J/cm² had been delivered. Further studies revealed that the concentrations of certain intracellular molecules varied in response to aBL irradiation. Coproporphyrin levels were found to decrease gradually, while ROS levels increased rapidly. Moreover, imaging revealed the emergence and increase of singlet oxygen molecules. Concomitantly, the lipid peroxidation product malondialdehyde (MDA) increased in abundance and intracellular K⁺ leakage was observed, indicating permeability of the cell membrane. Atomic force microscopy showed that the cell surface exhibited a coarse appearance. Finally, fatty acid profiles at different illumination levels were monitored by GC-MS. The relative amounts of three unsaturated fatty acids (C_16:1, C_20:1, and C_20:4) were decreased in response to aBL irradiation, which likely played a key role in the aforementioned membrane injuries. Collectively, these data suggest that the cell membrane is a major target of ROS during aBL irradiation, causing alterations to membrane lipid profiles, and in particular to the unsaturated fatty acid component.

Isolation and Transcriptome Analysis of Phenol-Degrading Bacterium From Carbon-Sand Filters in a Full-Scale Drinking Water Treatment Plant

Phenol is a typical organic contaminant in the environment. To date, the biodegradation of phenol by microorganisms remains the preferred method for its removal and remediation, but data on phenol removal by drinking water biofilters are lacking. In this study, we used high-throughput sequencing to investigate the microbial community structure in a carbon-sand biofilter. The results indicated that the predominant bacterial group was Bacilli, followed by Gammaproteobacteria, Clostridia, and Alphaproteobacteria. In addition, a strain was capable of degrading phenol at low concentrations of 500 μg/L within 100 min was isolated and identified as Rhodococcus sp. CS-1. Transcriptome analysis results showed that Rhodococcus sp. CS-1 was able to degrade phenol via both the catechol and protocatechuate branch of the β-ketoadipate pathway. Furthermore, some novel candidate biomarkers (copper oxidase, copper chaperone, and MarR/DeoR/TetR family transcriptional regulators) were successfully identified to be potentially involved in phenol biodegradation. This study indicates that carbon-sand filters have the potential for remediation of phenol. The application of native microorganisms to drinking water treatment system is an adaptive strategy in oligotrophic water environments.

Disinfection by Ozone Microbubbles Can Cause Morphological Change of Fusarium oxysporum f. sp. melonis Spores

To investigate the difference in the disinfectant efficiency of ozone microbubbles (O₃MB) and ozone millibubbles (O₃MMB), the morphological change of the treated Fusarium oxysporum f. sp. melonis spores was observed with scanning and transmission electron microscopies (SEM and TEM). The disinfectant efficiency of O₃MB on F. oxysporum f. sp. melonis spores was greater than that of O₃MMB. On observation with SEM, it was revealed that morphological change of F. oxysporum f. sp. melonis spores was caused by O₃MB and O₃MMB, and damage to the spore surfaces by O₃MB occurred sooner than that by O₃MMB. On observation with TEM, it was furthermore confirmed that F. oxysporum f. sp. melonis spores treated with O₃MB induced wavy deformation of cell membrane and the intracellular change different from that with O₃MMB. Therefore, the greater disinfection efficiency of O₃MB was suggested to be caused due to the function of the MB in addition to the oxidative power of O₃.

Spatiotemporal changes in bacterial community and microbial activity in a full-scale drinking water treatment plant

To gain insight into the bacterial dynamics present in drinking water treatment (DWT) systems, the microbial community and activity in a full-scale DWT plant (DWTP) in Guangzhou, South China, were investigated using Illumina Hiseq sequencing analyses combined with cultivation-based techniques during the wet and dry seasons. Illumina sequencing analysis of 16S rRNA genes revealed a large shift in the proportion of Actinobacteria, Proteobacteria and Firmicutes during the treatment process, with the proportion of Actinobacteria decreased sharply, whereas that of Proteobacteria and Firmicutes increased and predominated in treated water. Both microbial activity and bacterial diversity during the treatment process showed obvious spatial variation, with higher levels observed during the dry season and lower levels during the wet season. Clustering analysis and principal component analysis indicated dramatic shifts in the bacterial community after chlorination, suggesting that chlorination was highly effective at influencing the bacterial community. The bacterial community structure of finished water primarily comprised Pseudomonas, Citrobacter, and Acinetobacter, and interestingly showed high similarity to biofilms on granular activated carbon. Additionally, the abundance of bacterial communities was relatively stable in finished water and did not change with the season. A large number of unique operational taxonomic units were shared during treatment steps, indicating the presence of a diverse core microbiome throughout the treatment process. Opportunistic pathogens, including Pseudomonas, Acinetobacter, Citrobacter, Mycobacterium, Salmonella, Staphylococcus, Legionella, Streptococcus and Enterococcus, were detected in water including finished water, suggesting a potential threat to drinking-water safety. We also detected bacteria isolated from each treatment step using the pure-culture method. In particular, two isolates, identified as Mycobacterium sp. and Blastococcus sp., which belong to the phylum Actinobacteria, were obtained from finished water during the dry season. Together, these results provided evidence of spatial and temporal variations in DWTPs and contributed to the beneficial manipulation of the drinking water microbiome.

Changes in Microcystis aeruginosa cell integrity and variation in microcystin-LR and proteins during Tanfloc flocculation and floc storage

The objective of this study was to determine the influence of Tanfloc on Microcystis aeruginosa cell integrity, microcystin-LR (MC-LR), and proteins during flocculation and floc storage. The effects of Tanfloc addition, stirring, and floc storage time were considered to minimize cell damage and the release of MC-LR and proteins. Optimal flocculation conditions (Tanfloc dosage 10.42 mg L^-1, rapid agitation for 0.36 min at 568.88 rpm and slow agitation for 14.14 min at 12.1 rpm) were obtained using the response surface methodology. Up to 98.9% of the M. aeruginosa cells were removed intact at low Tanfloc dosage. During floc storage, Tanfloc initially protected the cells. After 8 d, large-scale cell lysis occurred because Tanfloc had substantially decomposed. Nevertheless, Tanfloc also extended the extracellular MC-LR and protein release time to 8 d. This delay ensured adequate time to decontaminate sludge containing the algae, thereby reducing the risk of secondary pollution. In addition, the low cost of Tanfloc facilitates its widespread application in the management of harmful algal blooms.

The Glutaredoxin Gene, grxB, Affects Acid Tolerance, Surface Hydrophobicity, Auto-Aggregation, and Biofilm Formation in Cronobacter sakazakii

Cronobacter species are foodborne pathogens that can cause neonatal meningitis, necrotizing enterocolitis, and sepsis; they have unusual abilities to survive in environmental stresses such as acid stress. However, the factors involved in acid stress responses and biofilm formation in Cronobacter species are poorly understood. In this study, we investigated the role of grxB on cellular morphology, acid tolerance, surface hydrophobicity, auto-aggregation (AAg), motility, and biofilm formation in Cronobacter sakazakii. The deletion of grxB decreased resistance to acid stresses, and notably led to weaker surface hydrophobicity, AAg, and biofilm formation under normal and acid stress conditions, compared with those of the wild type strain; however, motility was unaffected. Therefore, grxB appears to contribute to the survival of C. sakazakii in acid stresses and biofilm formation. This is the first report to provide valuable evidence for the role of grxB in acid stress responses and biofilm formation in C. sakazakii.

Combined effects of binary antibiotic mixture on growth, microcystin production, and extracellular release of Microcystis aeruginosa: application of response surface methodology

The interactive effects of binary antibiotic mixtures of spiramycin (SP) and ampicillin (AMP) on Microcystis aeruginosa (MA) in terms of growth as well as microcystin production and extracellular release were investigated through the response surface methodology (RSM). SP with higher 50 and 5% effective concentrations in MA growth was more toxic to MA than AMP. RSM model for toxic unit approach suggested that the combined toxicity of SP and AMP varied from synergism to antagonism with SP/AMP mixture ratio decreasing from reversed equitoxic ratio (5:1) to equitoxic ratio (1:5). Deviations from the prediction of concentration addition (CA) and independent action (IA) model further indicated that combined toxicity of target antibiotics mixed in equivalent ratio (1:1) varied from synergism to antagonism with increasing total dose of SP and AMP. With the increase of SP/AMP mixture ratio, combined effect of mixed antibiotics on MA growth changed from stimulation to inhibition due to the variation of the combined toxicity and the increasing proportion of higher toxic component (SP) in the mixture. The mixture of target antibiotics at their environmentally relevant concentrations with increased total dose and SP/AMP mixture ratio stimulated intracellular microcystin synthesis and facilitated MA cell lysis, thus leading to the increase of microcystin productivity and extracellular release.

Acinetobacter sp. DW-1 immobilized on polyhedron hollow polypropylene balls and analysis of transcriptome and proteome of the bacterium during phenol biodegradation process

Phenol is a hazardous chemical known to be widely distributed in aquatic environments. Biodegradation is an attractive option for removal of phenol from water sources. Acinetobacter sp. DW-1 isolated from drinking water biofilters can use phenol as a sole carbon and energy source. In this study, we found that Immobilized Acinetobacter sp. DW-1cells were effective in biodegradation of phenol. In addition, we performed proteome and transcriptome analysis of Acinetobacter sp. DW-1 during phenol biodegradation. The results showed that Acinetobacter sp. DW-1 degrades phenol mainly by the ortho pathway because of the induction of phenol hydroxylase, catechol-1,2-dioxygenase. Furthermore, some novel candidate proteins (OsmC-like family protein, MetA-pathway of phenol degradation family protein, fimbrial protein and coenzyme F390 synthetase) and transcriptional regulators (GntR/LuxR/CRP/FNR/TetR/Fis family transcriptional regulator) were successfully identified to be potentially involved in phenol biodegradation. In particular, MetA-pathway of phenol degradation family protein and fimbrial protein showed a strong positive correlation with phenol biodegradation, and Fis family transcriptional regulator is likely to exert its effect as activators of gene expression. This study provides valuable clues for identifying global proteins and genes involved in phenol biodegradation and provides a fundamental platform for further studies to reveal the phenol degradation mechanism of Acinetobacter sp.

Effects of ozone and chlorine disinfection on VBNC Helicobacter pylori by molecular techniques and FESEM images

Helicobacter pylori is a pathogen bacteria associated with chronic gastritis, peptic ulceration, and gastric carcinoma. H. pylori has a spiral morphology, which under certain conditions of stress becomes a coccoid form. This type of morphology has been linked to a viable but non-culturable (VBNC) state, which is thought to allow its persistence in the environment. Membrane damage in VBNC H. pylori in water as a mechanism for inactivation using ozone (O₃) and chlorine disinfection has not been reported in the literature. In this paper, disinfection assays with ozone and chlorine were conducted to evaluate their effects on VBNC H. pylori cells. The use of fluorescent dyes such as propidium monoazide (PMA) coupled with quantitative real-time polymerase chain reactions produced results necessary to assess the viability of the microorganism and demonstrate the effect of each disinfectant on the bacterial count. Applying ozone showed a 5-log bacterial reduction using a disinfectant concentration and exposure time (CT) of 4 mg min/L. Chlorine disinfection for the same 5-log reduction required a higher CT value. Field emission scanning electron microscope images of ozone-treated VBNC H. pylori also showed severe cell damage. The use of PMA revealed that chlorine produced physical damage in the membrane in addition to the known inhibiting effect on cell enzymatic processes. These findings are important for the detection and control of VBNC H. pylori cells in drinking water systems.

In vitro evaluation of wound healing and antimicrobial potential of ozone therapy

Although ozone therapy is extensively applied when wound repair and antimicrobial effect are necessary, little is known about cellular mechanisms regarding this process. Thus, this study aimed to evaluate ozone cytotoxicity in fibroblasts (L929) and keratinocytes (HaCaT) cell lines, its effects on cell migration and its antimicrobial activity. Cells were treated with ozonated phosphate-buffered saline (8, 4, 2, 1, 0.5 and 0.25 μg/mL ozone), chlorhexidine 0.2% or buffered-solution, and cell viability was determined through MTT assay. The effect of ozone on cell migration was evaluated through scratch wound healing and transwell migration assays. The minimum inhibitory concentrations for Candida albicans and Staphylococcus aureus were determined. Ozone showed no cytotoxicity for the cell lines, while chlorhexidine markedly reduced cell viability. Although no significant difference between control and ozone-treated cells was observed in the scratch assay, a considerable increase in fibroblasts migration was noticed on cells treated with 8 μg/mL ozonated solution. Ozone alone did not inhibit growth of microorganisms; however, its association with chlorhexidine resulted in antimicrobial activity. This study confirms the wound healing and antimicrobial potential of ozone therapy and presents the need for studies to elucidate the molecular mechanisms through which it exerts such biological effects.

Coagulation and oxidation for controlling ultrafiltration membrane fouling in drinking water treatment: Application of ozone at low dose in submerged membrane tank

Coagulation prior to ultrafiltration (UF) is widely applied for treating contaminated surface water sources for potable supply. While beneficial, coagulation alone is unable to control membrane fouling effectively in many cases, and there is continuing interest in the use of additional, complementary methods such as oxidation in the pre-treatment of raw water prior to UF. In this study, the application of ozone at low dose in the membrane tank immediately following coagulation has been evaluated at laboratory-scale employing model raw water. In parallel tests with and without the application of ozone, the impact of applied ozone doses of 0.5 mg L(-1) and 1.5 mg L(-1) (approximately 0.18 mg L(-1) and 0.54 mg L(-1) consumed ozone, respectively) on the increase of trans-membrane pressure (TMP) was evaluated and correlated with the quantity and nature of membrane deposits, both as a cake layer and within membrane pores. The results showed that a dose of 0.5 mgO3 L(-1) gave a membrane fouling rate that was substantially lower than without ozone addition, while a dose of 1.5 mgO3 L(-1) was able to prevent fouling effects significantly (no increase in TMP). Ozone was found to decrease the concentration of bacteria (especially the concentration of bacteria per suspended solid) in the membrane tank, and to alter the nature of dissolved organic matter by increasing the proportion of hydrophilic substances. Ozone decreased the concentration of extracellular polymeric substances (EPS), such as polysaccharides and proteins, in the membrane cake layer; the reduced EPS and bacterial concentrations resulted in a much thinner cake layer, although the suspended solids concentration was much higher in the ozone added membrane tank. Ozone also decreased the accumulation and hydrophobicity of organic matter within the membrane pores, leading to minimal irreversible fouling. Therefore, the application of low-dose ozone within the UF membrane tank is a potentially important approach for fully mitigating membrane fouling.

Subcellular mechanism of Escherichia coli inactivation during electrochemical disinfection with boron-doped diamond anode: A comparative study of three electrolytes

Although the identification of effective oxidant species has been extensively studied, yet the subcellular mechanism of bacterial inactivation has never been clearly elucidated in electrochemical disinfection processes. In this study, subcellular mechanism of Escherichia coli inactivation during electrochemical disinfection was revealed in terms of comprehensive factors such as cell morphology, total organic components, K(+) leakage, membrane permeability, lipid peroxidation, membrane potential, membrane proteins, intracellular enzyme, cellular ATP level and DNA. The electrolysis was conducted with boron-doped diamond anode in three electrolytes including chloride, sulfate and phosphate. Results demonstrated that cell inactivation was mainly attributed to damage to the intracellular enzymatic systems in chloride solution. In sulfate solution, certain essential membrane proteins like the K(+) ion transport systems were eliminated. Thus, the pronounced K(+) leakage from cytosol resulted in gradual collapse of the membrane potential, which would hinder the subcellular localization of cell division-related proteins as well as ATP synthesis and thereby lead to the bacterial inactivation. Remarkable lipid peroxidation was observed, while the intracellular damage was negligible. In phosphate solution, the cells sequentially underwent overall destruction as a whole cell with no captured intermediate state, during which the organic components of the cells were mostly subjected to mineralization. This study provided a thorough insight into the bacterial inactivation mechanism on the subcellular level.

Flow cytometric evaluation of physico-chemical impact on Gram-positive and Gram-negative bacteria

Since heat sensitivity of fruits and vegetables limits the application of thermal inactivation processes, new emerging inactivation technologies have to be established to fulfill the requirements of food safety without affecting the produce quality. The efficiency of inactivation treatments has to be ensured and monitored. Monitoring of inactivation effects is commonly performed using traditional cultivation methods which have the disadvantage of the time span needed to obtain results. The aim of this study was to compare the inactivation effects of peracetic acid (PAA), ozonated water (O3), and cold atmospheric pressure plasma (CAPP) on Gram-positive and Gram-negative bacteria using flow cytometric methods. E. coli cells were completely depolarized after treatment (15 s) with 0.25% PAA at 10°C, and after treatment (10 s) with 3.8 mg l(-1) O3 at 12°C. The membrane potential of CAPP treated cells remained almost constant at an operating power of 20 W over a time period of 3 min, and subsequently decreased within 30 s of further treatment. Complete membrane permeabilization was observed after 10 s O3 treatment, but treatment with PAA and CAPP did not completely permeabilize the cells within 2 and 4 min, respectively. Similar results were obtained for esterase activity. O3 inactivates cellular esterase but esterase activity was detected after 4 min CAPP treatment and 2 min PAA treatment. L. innocua cells and P. carotovorum cells were also permeabilized instantaneously by O3 treatment at concentrations of 3.8 ± 1 mg l(-1). However, higher membrane permeabilization of L. innocua and P. carotovorum than of E. coli was observed at CAPP treatment of 20 W. The degree of bacterial damage due to the inactivation processes is highly dependent on treatment parameters as well as on treated bacteria. Important information regarding the inactivation mechanisms can be obtained by flow cytometric measurements and this enables the definition of critical process parameters.

The performance of chitosan/montmorillonite nanocomposite during the flocculation and floc storage processes of Microcystis aeruginosa cells

This study aimed to investigate the performance of chitosan-modified nano-sized montmorillonite (CTS/NMMT) during the flocculation of Microcystis aeruginosa (MA). The release of intracellular microcystins (MCs) caused by the damage of intact MA cells during the flocculation and floc storage processes was also comprehensively evaluated through scanning electron microscopy (SEM) and measurement of K(+) and Mg(2+) release. With the application of the Box-Behnken experimental design combined with response surface methodology, the quadratic statistical model was established to predict and optimize the interactive effects of content of CTS/NMMT, weight ratio of NMMT to CTS, and agitation time on the removal efficiency of MA cells. A maximum removal of 94.7 % MA cells was observed with content of CTS/NMMT 300-320 mg L(-1), weight ratio of NMMT to CTS 14-16, and agitation time 16-50 min. During the flocculation process, CTS/NMMT aggregated MA cells as flocs and served as a protection shield for cells. The extracellular and intracellular microcystin-leucine-arginine (MC-LR) decreased remarkably and the yield of intracellular MC-LR showed a decreasing trend during the flocculation. The cell integrity was slightly damaged by the mechanical actions rather than by the flocculant. During the floc storage process, cell lysis and membrane damage were remarkably aggravated. The noticeable increase of K(+) and Mg(2+) release indicated that CTS/NMMT damaged the integrity of most MA cells in the flocs and liberated the intracellular MC-LR. Meanwhile, NMMT and CTS polymers assisted the adsorptive removal of extracellular MC-LR released to water. The flocs should be timely treated within 12 h to prevent the leakage of MCs.

UV disinfection induces a VBNC state in Escherichia coli and Pseudomonas aeruginosa

The occurrence of a viable but nonculturable (VBNC) state in bacteria may dramatically underestimate the health risks associated with drinking water. Therefore, the potential for UV treatment to induce a VBNC state in Escherichia coli and Pseudomonas aeruginosa was investigated. UV disinfection effectively reduced the culturability of E. coli and P. aeruginosa, with the destruction of nucleic acids demonstrated using gadA long gene fragment qPCR amplification. Following UV radiation, copy numbers for the high transcriptional levels of the 16S rRNA gene varied insignificantly in both strains, confirming results from plate counting assays indicating that VBNC states were induced in both strains. Furthermore, the virulence genes gadA and oprL remained highly expressed, suggesting that the VBNC bacteria still displayed pathogenicity. Propidium monoazide qPCR indicated that cell membranes remained intact even at a UV dose of 300 mJ/cm(2). The RT-qPCR results after UV and chlorine treatments in E. coli were significantly different (8.41 and 5.59 log units, respectively), further confirming the induction of VBNC bacteria induced by UV radiation. Finally, resuscitation was achieved, with E. coli showing greater resuscitation ability than P. aeruginosa. These results systematically revealed the potential health risks of UV disinfection and strongly suggest a combined disinfection strategy.

What is the best strategy for enhancing the effects of topically applied ozonated oils in cutaneous infections?

Owing to diabetes, atherosclerosis, and ageing, there are several million patients undergoing skin lesions degenerated into infected ulcers with very little tendency to heal and implying a huge socioeconomical cost. Previous medical experience has shown that the daily application of ozonated oil eliminates the infection and promotes a rapid healing. The purpose of the study is the optimization of the antimicrobial effect of ozonated oils by testing in vitro four bacterial species and one yeast without or in the presence of different amounts of human serum. The results obtained suggest that a gentle and continuous removal of debris and exudate is an essential condition for the potent bactericidal effect of ozonated oils. In fact, even small amounts of human serum inactivate ozone derivatives and protect bacteria. The application of ozonated oil preparations is very promising in a variety of skin and mucosal infections. Moreover, ozonated oils are far less expensive than antibiotic preparations.