Chlorine-resistant Bacteria Research Articles

Enhanced removal of biolabile oxygen-depleted dissolved organic matter by coagulation-adsorption process Improves biological stability of reclaimed water

Ensuring biological stability, signifying the maintenance of an unchanged bacterial concentration and composition during water distribution, is essential for mitigating the microbial hazards of reclaimed water. However, the interplay between chlorine-resistant bacteria (CRB) regrowth and molecular transformation of biodegradable organic matter in chlorinated reclaimed water distribution system remain unclear. This work investigated the transformation of dissolved organic matter (DOM) in reclaimed water treated by coagulation and by coagulation-adsorption over a 20-day incubation following chlorination, as well as its interactions with CRB through high-resolution mass spectrometer and high-throughput sequencing. The DOM biotransformation profile and DOM-bacteria interaction network collectively revealed the overall substrate preference and metabolic pattern of CRB (e.g., Methylobacterium-Methylorubrum, Acidovorax, and Sphingomonas), which evinced a propensity for utilizing oxygen-depleted DOM (O/C < 0.5) and producing oxygen-enriched DOM (O/C > 0.4). The incorporation of powdered activated carbon during coagulation markedly decreased the level of biodegradable DOM (4.33 mg C/L) and subsequently retarded the regrowth of CRB by one day compared to coagulation alone, attributable to the selective adsorption of DOM molecules with low O/C onto the activated carbon. This work underscores the critical role of the enhanced removal of oxygen-depleted DOM in ameliorating the biological stability of waters.

Ozone-Resistant Bacteria, an Inconvenient Hazard in Water Reclamation: Resistance Mechanism, Propagating Capacity, and Potential Risks.

Resistant bacteria have always been of research interest worldwide. In the urban water system, the increased disinfectant usage gives more chances for undesirable disinfection-resistant bacteria. As the strongest oxidative disinfectant in large-scale water treatment, ozone might select ozone-resistant bacteria (ORB), which, however, have rarely been reported and are inexplicit for their resistant mechanisms and physiological characteristics. In this study, six strains of ORB were screened from a water reclamation plant in Beijing. Three of them (O7, CR19, and O4) were more resistant to ozone than all previously reported ORB or even spores. The ozone consumption capacity of extracellular polymeric substances and cell walls was proved to be the main sources of bacterial ozone resistance, rather than intracellular antioxidant enzymes. The transcriptome results elucidated that strong ORB possessed a combined antioxidant mechanism consisting of the enhanced transcription of protein synthesis, protein export, and polysaccharide export genes (LptF, LptB, NodJ, LivK, LviG, MetQ, MetN, and GltU). This study confirmed the existence of ORB in urban water systems and brought doubts to the idea of a traditional control strategy against chlorine-resistant bacteria. A salient "trade-off" effect between the ozone resistance and propagation ability indicated the weakness and potential control approaches of ORB.

Occurrence of chlorine-resistant Pseudomonas aeruginosa in hospital water systems: threat of waterborne infections for patients

BackgroundSeveral healthcare-associated infection outbreaks have been caused by waterborne Pseudomonas aeruginosa exhibiting its ability to colonize water systems and resist conventional chlorine treatment. This study aims to investigate the occurrence of Pseudomonas aeruginosa in hospital drinking water systems and the antimicrobial resistance profiles (antibiotic and chlorine resistance) of isolated strains.MethodsWe investigated the presence of Pseudomonas aeruginosa in water and biofilms developed in nine hospital water systems (n = 192) using culture-based and molecular methods. We further assessed the survival of isolated strains after exposure to 0.5 and 1.5 ppm concentrations of chlorine. The profile of antibiotic resistance and presence of antibiotic resistance genes in isolated strains were also investigated.ResultsUsing direct PCR method, Pseudomonas aeruginosa was detected in 22% (21/96) of water and 28% (27/96) of biofilm samples. However, culturable Pseudomonas aeruginosa was isolated from 14 samples. Most of P. aeruginosa isolates (86%) were resistant to at least one antibiotic (mainly β-lactams), with 50% demonstrating multidrug resistance. Moreover, three isolates harbored intI1 gene and two isolates contained blaOXA−24,blaOXA−48, and blaOXA−58‌ genes. Experiments with chlorine disinfection revealed that all tested Pseudomonas aeruginosa strains were resistant to a 0.5 ppm concentration. However, when exposed to a 1.5 ppm concentration of chlorine for 30 min, 60% of the strains were eliminated. Interestingly, all chlorine-resistant bacteria that survived at 30-minute exposure to 1.5 ppm chlorine were found to harbor the intI1 gene.ConclusionsThe detection of antimicrobial resistant Pseudomonas aeruginosa in hospital water systems raises concerns about the potential for infections among hospitalized patients. The implementation of advanced mitigation measures and targeted disinfection methods should be considered to tackle the evolving challenges within hospital water systems.

Factors influencing the inactivation of Bacillus subtilis by epigallocatechin gallate (EGCG)

ABSTRACT Epigallocatechin gallate (EGCG) is an exceptional plant polyphenol for drinking water disinfection, due to its lasting antibacterial capabilities and broad spectrum of health benefits. Nevertheless, its effectiveness and the underlying mechanisms against chlorine-resistant bacteria, such as Bacillus subtilis, have not been thoroughly explored under various water conditions. The study at hand probed the inactivation rates of EGCG on B. subtilis was subjected to different concentrations, contact times, acidic or basic environments, and temperatures; biological mechanisms were examined by analyzing alkaline phosphatase, proteins, glucose, ATP, and redox biomolecules. Results indicated a positive correlation between EGCG concentration and the inactivation rate of B. subtilis, with the rate notably rising at EGCG levels below 800 mg/l and under acidic pH. The inactivation efficiency increased with temperature increments from 25 to 45 °C. Moreover, EGCG exerted a detrimental impact on the structural integrity, energy metabolism, and the antioxidant defense system of B. subtilis showed a dose-dependent antimicrobial activity against Escherichia coli. Consequently, this study provides a strong foundation for evaluating EGCG's efficacy against chlorine-resistant bacteria, promoting its theoretical application for drinking water treatment and guiding methodological advancements for broader applications.

Synergistic ferrate(VI) and chlorine for reclaimed water disinfection: Microbial control and chlorine decay mitigation

Chlorination is the most widely used disinfection technology due to its simplicity and continuous disinfection ability. However, the drawbacks of disinfection by-products and chlorine-resistant bacteria have gained increasing attention. Nowadays, ferrate (Fe(VI)) is a multifunctional and environmentally friendly agent which has great potential in wastewater reclamation and reuse. This study investigated synergistic Fe(VI) and chlorine technology for reclaimed water disinfection in terms of microbial control and chlorine decay mitigation. Specifically, synergistic disinfection significantly improved the inactivation efficiency on total coliform, Escherichia coli and heterotrophic bacteria compared to sole chlorination. Synergistic disinfection also exhibited superior performance on controlling the relative abundance of chlorine-resistant bacteria and pathogenic bacteria. In addition, the decay rate of residual chlorine was relatively lower after Fe(VI) pretreatment, which was beneficial for microbial control during the reclaimed water distribution process. Technical and economic analyses revealed that synergistic Fe(VI) and chlorine disinfection was suitable and feasible. Results of this study are believed to provide useful information and alternative options on the optimization of reclaimed water disinfection.

Enhancement of chlorine-resistant bacteria inactivation via coupling Magnéli phase Ti4O7-based electrochemical oxidation and chlorination

The widespread use of chlorination prompts the selection of chlorine-resistant bacteria in drinking water, posing a great threat to public health. Herein, according to sequential electrochemical oxidation/reduction (Ox/Red) processes with a flow-through mode, electrochemical devices (ED) with sequential Ox-Red, Red-Ox and Ox-Red-Ox processes were coupled with chlorination (AC) to evaluate their synergistic effects and mechanisms for inactivation of chlorine-resistant bacteria in drinking water. ED/AC enabled ∼ 3.0 log of synergistic effect and ∼ 2.5 times lower energy consumption for inactivation of various chlorine-sensitive/-resistant bacteria and gram-positive/-negative bacteria in DI and tap waters. Especially, ED/AC with Ox-Red-Ox device exhibited the best disinfection performance with achieving over 6.7 log inactivation of Bacillus cereus at 4.0 V and 0.5 mg/L-Cl2 as compared with ED alone (∼1.25 log) and AC (∼2.67 log) disinfection. The electrochemical oxidation on Ti4O7-based anode promoted the generation of free chlorine radicals and H+ ions, which was accompanied with the formation of neutral HClO molecules. Characterizations of SEM and flow cytometer suggested that oxidative species of neutral HClO molecules and free chlorine radicals enhanced the bacterial inactivation via severe damages of cell structures. This work provided a promising strategy via coupling electrochemical oxidation and chlorination for eliminating chlorine-resistant bacteria in drinking water.

Study on the inactivation effect and mechanism of EGCG disinfectant on Bacillus subtilis

The widespread use of chlorine-based disinfectants in drinking water treatment has led to the proliferation of chlorine-resistant bacteria and the risk of disinfection byproducts (DBPs), posing a serious threat to public health. This study aims to explore the effectiveness and potential applications of epigallocatechin gallate (EGCG) against chlorine-resistant Bacillus and its spores in water, providing new insights for the control of chlorine-resistant bacteria and improving the biological stability of distribution systems. The inactivation effects of EGCG on Bacillus subtilis (B. subtilis) and its spores were investigated using transmission electron microscopy, ATP measurement, and transcriptome sequencing analysis to determine changes in surface structure, energy metabolism, and gene expression levels, thereby elucidating the inactivation mechanism. The results demonstrate the potential application of EGCG in continuously inhibiting chlorine-resistant B. subtilis in water, effectively improving the biological stability of the distribution system. However, EGCG is not suitable for treating raw water with high spore content and is more suitable as a supplementary disinfectant for processes with strong spore removal capabilities, such as ozone, ultraviolet, or ultrafiltration. EGCG exhibits a disruptive effect on the morphological structure and energy metabolism of B. subtilis and suppresses the synthesis of substances, energy metabolism, and normal operation of the antioxidant system by inhibiting the expression of multiple genes, thereby achieving the inactivation of B. subtilis.

Full-length 16S rRNA gene sequencing reveals the operating mode and chlorination-aggravated SWRO biofouling at a nuclear power plant.

Reverse osmosis (RO) membrane fouling and biological contamination problems faced by seawater desalination systems are microbiologically related. We used full-length 16S rRNA gene sequencing to assess the bacterial community structure and chlorine-resistant bacteria (CRB) associated with biofilm growth in different treatment processes under the winter mode of a chlorinated seawater desalination system in China. At the outset of the winter mode, certain CRB, such as Acinetobacter, Pseudomonas, and Bacillus held sway over the bacterial community structure, playing a pivotal role in biofouling. At the mode's end, Deinococcus and Paracoccus predominated, with Pseudomonas and Roseovarius following suit, while certain CRB genera still maintained their dominance. RO and chlorination are pivotal factors in shaping the bacterial community structure and diversity, and increases in total heterotrophic bacterial counts and community diversity in safety filters may adversely affect the effectiveness of subsequent RO systems. Besides, the bacterial diversity and culturable biomass in the water produced by the RO system remain high, and some conditionally pathogenic CRBs pose a certain microbial risk as a source of drinking water. Targeted removal of these CRBs will be an important area of research for advancing control over membrane clogging and ensuring water quality safety in the future.

The resistance change and stress response mechanisms of chlorine-resistant bacteria under microplastic stress in drinking water distribution system

The presence of both chlorine-resistant bacteria (CRB) and microplastics (MPs) in drinking water distribution systems (DWDS) poses a threat to water quality and human health. However, the risk of CRB bio evolution under the stress of MPs remains unclear. In this study, polypropylene (PP) and polyethylene (PE) were selected to study the adsorption and desorption behavior of sulfamethoxazole (SMX), and it was clear that MPs had the risk of carrying pollutants into DWDS and releasing them. The results of the antibiotic susceptibility test and disinfection experiment confirmed that MPs could enhance the resistance of CRB to antibiotics and disinfectants. Bacteria epigenetic resistance mechanisms were approached from multiple perspectives, including physiological and biochemical characteristics, as well as molecular regulatory networks. When MPs enter DWDS, CRB could attach to the surface of MPs and directly interact with both MPs and the antibiotics they release. This attachment process promoted changes in the composition and content of extracellular polymers (EPS) within cells, enhanced surface hydrophobicity, stimulated oxidative stress function, and notably elevated the relative abundance of certain antibiotic resistance genes (ARGs). This study elucidates the mechanism by which MPs alter the intrinsic properties of CRB, providing valuable insights into the effective avoidance of biological risks to water quality during CRB evolution.

Comprehensive assessment of chlorination disinfection on microplastic-associated biofilms

Chlorination on microplastic (MP) biofilms was comprehensively investigated with respect to disinfection efficiency, morphology, and core microbiome. The experiments were performed under various conditions: i) MP particles; polypropylene (PP) and polystyrene (PS), ii) MP biofilms; Escherichia coli for single-species and river water microorganisms for multiple-species, iii) different chlorine concentrations, and iv) different chlorine exposure periods. As a result, chlorination effectively inactivated the MP biofilm microorganisms. The disinfection efficiency increased with increasing the free chlorination concentration and exposure periods for both single- and multiple-species MP biofilms. The multiple-species MP biofilms were inactivated 1.3–6.0 times less than single-species MP biofilms. In addition, the PP-MP biofilms were more vulnerable to chlorination than the PS-MP biofilms. Morphology analysis verified that chlorination detached most MP biofilms, while a small part still remained. Interestingly, chlorination strongly changed the biofilm microbiome on MPs; the relative abundance of some microbes increased after the chlorination, suggesting they could be regarded as chlorine-resistant bacteria. Some potential pathogens were also remained on the MP particles after the chlorination. Notably, chlorination was effective in inactivating the MP biofilms. Further research should be performed to evaluate the impacts of residual MP biofilms on the environment.

Comparative analysis of chlorine-resistant bacteria after chlorination and chloramination in drinking water treatment plants

Chlorine-resistant bacteria (CRB) in drinking water treatment plants (DWTPs) jeopardize water quality and pose a potential risk to human health. However, the specific response of CRB to chlorination and chloramination remains uncharacterized. Therefore, we analyzed 16 S rRNA sequencing data from water samples before and after chlorination and chloramination taken between January and December 2020. Proteobacteria and Firmicutes dominated all finished water samples. After chloramination, Acinetobacter, Pseudomonas, Methylobacterium, Ralstonia, and Sphingomonas were the dominant CRB, whereas Ralstonia, Bacillus, Acinetobacter, Pseudomonas, and Enterococcus were prevalent after chlorination. Over 75% of the CRB e.g. Acinetobacter, Pseudomonas, Bacillus, and Enterococcus were shared between the chlorination and chloramination, involving potentially pathogens, such as Acinetobacter baumannii and Pseudomonas aeruginosa. Notably, certain genera such as Faecalibacterium, Geobacter, and Megasphaera were enriched as strong CRB after chloramination, whereas Vogesella, Flavobacterium, Thalassolituus, Pseudoalteromonas, and others were enriched after chlorination according to LEfSe analysis. The shared CRB correlated with temperature, pH, and turbidity, displaying a seasonal pattern with varying sensitivity to chlorination and chloramination in cold and warm seasons. These findings enhance our knowledge of the drinking water microbiome and microbial health risks, thus enabling better infectious disease control through enhanced disinfection strategies in DWTPs.

Biofilm Formation in Water Distribution Systems

A biofilm is a biologically active matrix attached to the surface of cells and their extracellular products. As they are a mixture of many microorganisms, the microbiological activity of biofilms varies according to their position in the aggregate. With particular emphasis on drinking water distribution systems, this review focuses on the process of biofilm formation, associated bacteria, chlorine resistance of bacteria, and the predominant surface materials. We have compiled studies on the bacteria in drinking water distribution systems and their interactions with biofilm formation on different materials, and we also analysed the chlorine-resistant bacteria and their problems in the water networks. The materials used in the drinking water network are significantly affected by the disinfection method used to produce the biofilm that adheres to them. Some studies propose that the material is inconsequential, with the disinfection process being the most significant factor. Studies suggest that materials based on plastics (such as PVC and HDPE) tend to be more effective in controlling biofilm formation or removal than those based on metals (such as stainless steel), which have been found to be less effective in some instances. Chlorine-resistant strains are becoming more and more common in drinking water networks, resulting in the occurrence of diseases such as typhus and cholera.

Incidence of co-resistance to antibiotics and chlorine in bacterial biofilm of hospital water systems: Insights into the risk of nosocomial infections

The presence of biofilms in drinking water distribution systems (DWDS) in healthcare settings poses a considerable risk to the biological security of water, particularly when the biofilm bacteria demonstrate antimicrobial resistance characteristics. This study aimed to investigate the occurrence of antibiotic-resistant bacteria (ARB) in biofilms within DWDS of hospitals. The chlorine resistance of the isolated ARB was analyzed, and then chlorine-resistant bacteria (CRB) were identified using molecular methods. Additionally, the presence of several antibiotic resistance genes (ARGs) was monitored in the isolated ARB. Out of the 41 biofilm samples collected from hospitals, ARB were detected in 32 (78%) of the samples. A total of 109 colonies of ARB were isolated from DWDS of hospitals, with β-lactam resistant bacteria, including ceftazidime-resistant and ampicillin-resistant bacteria, being the most frequently isolated ARB. Analyzing of ARGs revealed the highest detection of aac6, followed by sul1 gene. However, the β-lactamase genes blaCTX-M and blaTEM were not identified in the ARB, suggesting the presence of other β-lactamase genes not included in the tested panel. Exposure of ARB to free chlorine at a concentration of 0.5 mg/l showed that 64% of the isolates were CRB. However, increasing the chlorine concentration to 4 mg/l decreased the high fraction of ARB (91%). The domi‌‌nant CRB identified were Sphingomonas, Brevundimonas, Stenotrophomonas, Bacillus and Staphylococcus with Bacillus exhibiting the highest frequency. The results highlight the potential risk of biofilm formation in the DWDS of hospitals, leading to the dissemination of ARB in hospital environments, which is a great concern for the health of hospitalized patients, especially vulnerable individuals. Surveillance of antimicrobial resistance in DWDS of hospitals can provide valuable insights for shaping antimicrobial use policies and practices that ensure their efficacy.

Residual chlorine persistently changes antibiotic resistance gene composition and increases the risk of antibiotic resistance in sewer systems

During the COVID-19 pandemic, excessive amounts of disinfectants and their transformation products entered sewer systems worldwide, which was an extremely rare occurrence before. The stress of residual chlorine and disinfection by-products is not only likely to promote the spread of antibiotic resistance genes (ARGs), but also leads to the enrichment of chlorine-resistant bacteria that may also be resistant to antibiotics. Therefore, the potential impact of such discharge on ARG composition should be studied and the health risks should be assessed. Thus, this study combined high-throughput 16S rRNA gene amplicon sequencing and metagenomic analysis with long-term batch tests that involved two stages of stress and recovery to comprehensively evaluate the impact of residual chlorine on the microbial community and ARG compositions in sewer systems. The tests demonstrated that the disturbance of the microbial community structure by residual chlorine was reversible, but the change in ARG composition was persistent. This study found that vertical propagation and horizontal gene transfer jointly drove ARG composition succession in the biofilm, while the driving force was mainly horizontal gene transfer in the sediment. In this process, the biocide resistance gene (BRG) subtype chtR played an important role in promoting co-selection with ARGs through plasmids and integrative and conjugative elements. Moreover, it was further shown that the addition of sodium hypochlorite increased the risk of ARGs to human health, even after discontinuation of dosing, signifying that the impact was persistent. In general, this study strengthens the co-selection theory of ARGs and BRGs, and calls for improved disinfection strategies and more environmentally friendly disinfectants.

Inactivation of chlorine-resistant bacteria (CRB) via various disinfection methods: Resistance mechanism and relation with carbon source metabolism

With the widespread use of chlorine disinfection, chlorine-resistant bacteria (CRB) in water treatment systems have gained public attention. Bacterial chlorine resistance has been found positively correlated with extracellular polymeric substance (EPS) secretion. In this study, we selected the most suitable CRB controlling method against eight bacterial strains with different chlorine resistance among chloramine, ozone, and ultraviolet (UV) disinfection, analyzed the resistance mechanisms, clarified the contribution of EPS to disinfection resistance, and explored the role of carbon source metabolism capacity. Among all the disinfectants, UV disinfection showed the highest disinfection capacity by achieving the highest average and median log inactivation rates for the tested strains. For Bacillus cereus CR19, the strain with the highest chlorine resistance, 40 mJ/cm2 UV showed a 1.90 log inactivation, which was much higher than that of 2 mg-Cl2/L chlorine (0.67 log), 2 mg-Cl2/L chloramine (1.68 log), and 2 mg/L ozone (0.19 log). Meanwhile, the UV resistance of the bacteria did not correlate with EPS secretion. These characteristics render UV irradiation the best CRB controlling disinfection method. Chloramine was found to have a generally high inactivation efficiency for bacteria with high chlorine-resistance, but a low inactivation efficiency for low chlorine-resistant ones. Although EPS consumed up to 56.7% of chloramine which an intact bacterial cell consumed, EPS secretion could not explain chloramine resistance. Thus, chloramine is an acceptable CRB control method. Similar to chlorine, ozone generally selected high EPS-secreting bacteria, with EPS consuming up to 100% ozone. Therefore, ozone is not an appropriate method for controlling CRB with high EPS secretion. EPS played an important role in all types of disinfection resistance, and can be considered the main mechanism for bacterial chlorine and ozone disinfection resistance. However, as EPS was not the main resistance mechanism in UV and chloramine disinfection, CRB with high EPS secretion were inactivated more effectively. Furthermore, carbon source metabolism was found related to the multiple resistance of bacteria. Those with low carbon source metabolism capacity tended to have higher multiple resistance, especially to chlorine, ozone, and UV light. Distinctively, among the tested gram-negative bacteria, in contrast to other disinfectants, chloramine resistance was negatively correlated with EPS secretion and positively correlated with carbon source metabolism capacity, suggesting a special disinfection mechanism.

Differential Expression of Antioxidant Enzymes in Chlorine-Resistant Acinetobacter and Serratia spp. Isolated from Water Distribution Sites in Mumbai: A Study on Mechanisms of Chlorine Resistance for Sustainable Water Treatment Strategies

Chlorination is a widely used process for disinfecting drinking water, but the emergence of chlorine-resistant bacteria has become a significant concern. While previous research has focused on identifying chlorine-resistant organisms, there has been limited investigation into the mechanisms behind chlorine resistance. Some bacterial isolates that display resistance to chlorine treatment may protect themselves using various mechanisms, including biofilm production, antibiotic resistance, horizontal transfer of antibiotic resistance genes, or producing antioxidant enzymes. Given that chlorination employs hypochlorous acid (HOCl), which is an extremely potent oxidizing agent, the most critical mechanism to investigate is antioxidant enzymes. This study investigated the antioxidant profile of eight chlorine-resistant isolates (three of the Serratia sp. and five of the Acinetobacter) after chlorine exposure. The profiles, both between and within species, were noticeably different. Among the isolates, Acinetobacter junii NA 3-2 showed a significant increase in the specific activity of superoxide dismutase, catalase, and ascorbate peroxidase after exposure to 20 ppm chlorine. In the guaiacol peroxidase (GPX) assay, only isolates belonging to Serratia marcescens showed GPX activity, and Serratia marcescens 3929-1 showed significant increase after exposure to 20 ppm of chlorine. None of the isolates belonging to Acinetobacter spp. showed GPX activity. Additionally, almost all control samples exhibited some enzyme activity, which may explain their survival against chlorine treatment in reservoirs. Principal component analysis revealed no strain-dependent similarities, while the balance of scavenging enzymes changed, as demonstrated in the heat map. Thus, this study suggests that antioxidant enzymes may be one mechanism of protection for some bacterial species against oxidative stress from chlorination, resulting in chlorine resistance. Understanding the mechanism of chlorine resistance is critical to identifying potential solutions. This study highlights the need to consider more modern approaches to disinfecting drinking water.

Chlorine-resistant bacteria in drinking water: Generation, identification and inactivation using ozone-based technologies

Along with the expansion of cities and population growth, the demand for drinking water is increasing. Chlorine, the most common method of disinfection, is often used in the disinfection process of drinking water plants. Residual chlorine is routinely added to the water delivery network as an additive for continuous disinfection to ensure water safety from the drinking water pipelines to the customer's taps. However, some organisms can still survive even in conditions of high chlorine concentration. This also poses a significant risk to the safety of drinking water. This review investigates the origin of chlorine-resistant bacteria in drinking water networks, the species of chlorine-resistant bacteria found in recent years and the conventional methods of identification of chlorine-resistant bacteria, the current inactivation techniques for chlorine-resistant bacteria are also summarized. The research on inactivation of chlorine-resistant bacteria by ozone-based and other methods are especially highlighted.

Study on the distribution characteristics and metabolic mechanism of chlorine-resistant bacteria in indoor water supply networks

The presence and attachment of chlorine-resistant bacteria on the surface of water distribution network will deteriorate water quality and threaten human health. Chlorination is critical in drinking water treatment to ensure the biosafety of drinking water. However, how disinfectants affect the structures of dominant flora during biofilm development and whether the changes are consistent with the free flora remain unclear. Therefore, we investigated changes in species diversity and relative abundance of different bacterial communities in planktonic and biofilm samples at different chlorine residual concentrations (blank, 0.3 mg/L, 0.8 mg/L, 2.0 mg/L and 4.0 mg/L), and the main reasons for the development of chlorine resistance in bacteria was also discussed. The results showed that the richness of microbial species in the biofilm was higher than that in planktonic microbial samples. In the planktonic samples, Proteobacteria and Actinobacteria were the dominant groups regardless of the chlorine residual concentration. For biofilm samples, the dominant position of Proteobacteria bacteria was gradually replaced by actinobacteria bacteria with the increase of chlorine residual concentration. In addition, at higher chlorine residual concentration, Gram-positive bacteria were more concentrated to form biofilms. There are three main reasons for the generation of chlorine resistance of bacteria: enhanced function of efflux system, activated bacterial self-repair system, and enhanced nutrient uptake capacity.

Enhance antibiotic resistance and human health risks in aerosols during the COVID-19 pandemic

Aerosols are an important route for the transmission of antibiotic resistance genes (ARGs). Since the 2019 (COVID-19) pandemic, the large-scale use of disinfectants has effectively prevented the spread of environmental microorganisms, but studies regarding the antibiotic resistance of airborne bacteria remain limited. This study focused on four functional urban areas (commercial areas, educational areas, residential areas and wastewater treatment plant) to study the variations in ARG abundances, bacterial community structures and risks to human health during the COVID-19 pandemic in aerosol. The results indicated the abundance of ARGs during the COVID-19 period were up to approximately 13-fold greater than before the COVID-19 period. Large-scale disinfection resulted in a decrease in total bacterial abundance. However, chlorine-resistant bacteria tended to be survived. Among the four functional areas, the diversity and abundance of aerosol bacteria were highest in commercial aera. Antibiotic susceptibility assays suggested elevated resistance of isolated bacteria to several tested antibiotics due to disinfection exposure. The potential exposure risks of ARGs to human health were 2 times higher than before the COVID-19 pandemic, and respiratory intake was the main exposure route. The results highlighted the elevated antibiotic resistance of bacteria in aerosols that were exposed to disinfectants after the COVID-19 pandemic. This study provides theoretical guidance for the rational use of disinfectants and control of antimicrobial resistance.

Synergistic nanowire-assisted electroporation and chlorination for inactivation of chlorine-resistant bacteria in drinking water systems via inducing cell pores for chlorine permeation

The widespread use of chlorination (Cl2) in drinking water systems causes the selection of chlorine-resistant bacteria commonly with dense extracellular polymeric substance (EPS) against chlorine permeation, posing significant threat to public health. Herein, a nanowire-assisted electroporation (EP) via locally enhanced electric field was combined with Cl2 to construct the synergistic EP/Cl2 disinfection, with the purposes of inducing cell pores for chlorine permeation and bacterial inactivation. The synergistic effects of EP/Cl2 were observed for inactivation of chlorine-resistant Bacillus cereus (G+, 304 μg DOC-EPS/109 CFU) and Aeromonas media (G-, 35.8 μg), and chlorine-sensitive Escherichia coli (G-, 5.1 μg) that were frequent occurrence in drinking water systems. The EP/Cl2 enabled above 6 log B. cereus inactivation (undetectable live bacteria) at 1.5 V-EP and 0.9 mg/L-Cl2, which was much higher than the individual EP (1.11 log) and Cl2 (1.13 log) disinfection. The cell membrane integrity, intracellular free chlorine levels, and morphology analyses revealed that the electroporation-induced pores on cell wall/membrane destructed the bound EPS barrier for chlorine permeation, and the pore sizes were further enlarged by chlorine oxidation, hence facilitating bacterial inactivation via destroying the cell structures. The excellent disinfection performance for tap water and lake water also suggested its sound application potentials.