Inactivation of two Mycobacteria by free chlorine: Effectiveness, influencing factors, and mechanisms

Alleviation of RO membrane fouling in wastewater reclamation plants using an enhanced acid-base chemical cleaning method

Membrane fouling has always been a critical constraint in the operation of the reverse osmosis (RO) process, and chemical cleaning is essential for mitigating membrane fouling and ensuring smooth operation of the membrane system. This paper presents an optimized chemical cleaning method for the efficient cleaning of RO membranes in full-scale applications. Compared to the regular cleaning method (cleaning with 0.1 % NaOH + 1 % ethylenediaminetetraacetic acid + 0.025 % sodium dodecyl benzene sulfonate followed by 0.2 % HCl), the optimized cleaning method improves the cleaning efficiency by adding sodium chloride to the alkaline cleaning solution and citric acid to the acid cleaning solution. Notably, the membrane flux recovery rate with the optimized cleaning method is 45.74 %, and it improves the cleaning efficiency by 1.65 times compared to the regular cleaning method. Additionally, the optimized cleaning method removes 30.46 % of total foulants (organic and inorganic), which is 2.11 times higher than the regular cleaning method. The removal of inorganic ions such as Fe, Ca, and Mg is significantly improved with the optimized cleaning method. For organic matter removal, the optimized cleaning method effectively removes more polysaccharides, proteins, and microbial metabolites by disrupting the complex structures of organic matter. Furthermore, it also changes the microbial community structure on the RO membrane surface by eliminating microorganisms that cannot withstand strong acids, bases, and high salt environments. However, Mycobacterium can adapt to these harsh conditions, showing a relative abundance of up to 84.13 % after cleaning. Overall, our results provide a new chemical cleaning method for RO membranes in full-scale applications. This method effectively removes membrane foulants and enhances the understanding of the removal characteristics of foulants on RO membrane surfaces by chemical cleaning.

Pre-exposure to peracetic acid followed by UV treatment for deactivating vancomycin-resistant Enterococcus faecalis through intracellular attack

Antimicrobial resistance (AMR) poses a global health threat to aquatic environments and its propagation is a hot topic. Therefore, deactivating antibiotic-resistant bacteria (ARB) and removing antibiotic resistance genes (ARGs) from water is crucial for controlling AMR transmission. Peracetic acid (PAA), which is known for its potent oxidizing properties and limited by-product formation, is emerging as a favorable disinfectant for water treatment. In this study, we aimed to assess the efficacy of pre-exposure to PAA followed by UV treatment (PAA-UV/PAA) compared with the simultaneous application of UV and PAA (UV/PAA). The focus was on deactivating vancomycin-resistant Enterococcus faecalis (VREfs), a typical ARB in water. Pre-exposure to PAA significantly enhanced the efficacy of subsequent UV/PAA treatment. At a UV fluence of 7.2 mJ cm-2, the PAA-UV/PAA method achieved a 6.21 log reduction in VREfs, surpassing the 1.29 log reduction observed with UV/PAA. Moreover, compared to UV/PAA, PAA-UV/PAA showed increased efficacy with longer pre-exposure times and higher PAA concentrations, maintaining superior performance across a broad pH range and in the presence of humic acid. Flow cytometry analysis indicated minimal cellular membrane damage using both methods. However, the assessments of superoxide dismutase (SOD) activity and adenosine triphosphate content revealed that PAA-UV/PAA induced greater oxidative stress under similar UV irradiation conditions, leading to slower bacterial regrowth. Specifically, SOD activity in PAA-UV/PAA surged to 3.06 times its baseline, exceeding the 1.73-fold increase under UV/PAA conditions. Additionally, pre-exposure to PAA amplified ARGs degradation and reduced resistance gene leakage, effectively mitigating the spread of AMR. Pre-exposure to 200 μM PAA for 10 and 20 min enhanced vanB gene removal efficiency by 0.14 log and 1.29 log, respectively. Our study provides a feasible approach for optimizing UV/PAA disinfection for efficient removal of ARB and ARGs.

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.

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.

Microplastic pollution interaction with disinfectant resistance genes: research progress, environmental impacts, and potential threats

The consumption of disposable plastic products and disinfectants has surged during the global COVID-19 pandemic, as they play a vital role in effectively preventing and controlling the spread of the virus. However, microplastic pollution and the excessive or improper use of disinfectants contribute to the increased environmental tolerance of microorganisms. Microplastics play a crucial role as vectors for microorganisms and plankton, facilitating energy transfer and horizontal gene exchange. The increase in the use of disinfectants has become a driving force for the growth of disinfectant resistant bacteria (DRB). A large number of microorganisms can have intense gene exchange, such as plasmid loss and capture, phage transduction, and cell fusion. The reproduction and diffusion rate of DRB in the environment is significantly higher than that of ordinary microorganisms, which will greatly increase the environmental tolerance of DRB. Unfortunately, there is still a huge knowledge gap in the interaction between microplastics and disinfectant resistance genes (DRGs). Accordingly, it is critical to comprehensively summarize the formation and transmission routes of DRGs on microplastics to address the problem. This paper systematically analyzed the process and mechanisms of DRGs formed by microbes. The interaction between microplastics and DRGs and the contribution of microplastic on the diffusion and spread of DRGs were expounded. The potential threats to the ecological environment and human health were also discussed. Additionally, some challenges and future priorities were also proposed with a view to providing useful basis for further research.

Can microplastics and disinfectant resistance genes pose conceivable threats to water disinfection process?

Microplastic pollution in the environment has aroused widespread concerns, however, the potential environmental risks caused by excessive use of disinfectants are still unknown. Disinfectants with doses below the threshold can enhance the communication of resistance genes in pathogenic microorganisms, promoting the development and spread of antimicrobial activity. Problematically, the intensification of microplastic pollution and the increase of disinfectant consumption will become a key driving force for the growth of disinfectant resistance bacteria (DRB) and disinfectant resistance genes (DRGs) in the environment. Disinfection plays a crucial role in ensuring water safety, however, the presence of microplastics and DRGs seriously disturb the water disinfection process. Microplastics can reduce the concentration of disinfectant in the local environment around microorganisms and improve their tolerance. Microorganisms can improve their resistance to disinfectants or generate resistance genes via phenotypic adaptation, gene mutations, and horizontal gene transfer. However, very limited information is available on the impact of DRB and DRGs on disinfection process. In this paper, the contribution of microplastics to the migration and transmission of DRGs was analyzed. The challenges posed by the presence of microplastics and DRGs on conventional disinfection were thoroughly discussed. The knowledge gaps faced by relevant current research and further research priorities have been proposed in order to provide a scientific basis in the future.

Assessing the Impacts of Lead Corrosion Control on the Microbial Ecology and Abundance of Drinking-Water-Associated Pathogens in a Full-Scale Drinking Water Distribution System

Increases in phosphate availability in drinking water distribution systems (DWDSs) from the use of phosphate-based corrosion control strategies may result in nutrient and microbial community composition shifts in the DWDS. This study assessed the year-long impacts of full-scale DWDS orthophosphate addition on both the microbial ecology and density of drinking-water-associated pathogens that infect the immunocompromised (DWPIs). Using 16S rRNA gene amplicon sequencing and droplet digital PCR, drinking water microbial community composition and DWPI density were examined. Microbial community composition analysis suggested significant compositional changes after the orthophosphate addition. Significant increases in total bacterial density were observed after orthophosphate addition, likely driven by a 2 log 10 increase in nontuberculous mycobacteria (NTM). Linear effect models confirmed the importance of phosphate addition with phosphorus concentration explaining 17% and 12% of the variance in NTM and L. pneumophila density, respectively. To elucidate the impact of phosphate on NTM aggregation, a comparison of planktonic and aggregate fractions of NTM cultures grown at varying phosphate concentrations was conducted. Aggregation assay results suggested that higher phosphate concentrations cause more disaggregation, and the interaction between phosphate and NTM is species specific. This work reveals new insight into the consequences of orthophosphate application on the DWDS microbiome and highlights the importance of proactively monitoring the DWDS for DWPIs.

Actinobacteria produce taste and odor in drinking water reservoir: Community composition dynamics, co-occurrence and inactivation models

Taste and odor (T&O) has become a significant concern for drinking water safety. Actinobacteria are believed to produce T&O during the non-algal bloom period; however, this has not been widely investigated. In this study, the seasonal dynamics of the actinobacterial community structure and inactivation of odor-producing actinobacteria were explored. The results indicated that the diversity and community composition of actinobacteria exhibited significant spatiotemporal distribution. Network analysis and structural equation modeling showed that the actinobacterial community occupied a similar environmental niche, and the major environmental attributes exhibited spatiotemporal dynamics, which affected the actinobacterial community. Furthermore, the two genera of odorous actinobacteria were inactivated in drinking water sources using chlorine. Amycolatopsis spp. have a stronger chlorine resistance ability than Streptomyces spp., indicating that chlorine inactivates actinobacteria by first destroying cell membranes and causing the release of intracellular compounds. Finally, we integrated the observed variability in the inactivation rate of actinobacteria into an expanded Chick-Watson model to estimate its effect on inactivation. These findings will deepen our understanding of the seasonal dynamics of actinobacterial community structure in drinking water reservoirs and provide a foundation for reservoir water quality management strategies.

Effect of NaClO and ClO2 on the bacterial properties in a reclaimed water distribution system: efficiency and mechanisms

Extensive application of reclaimed water alleviated water scarcity obviously. Bacterial proliferation in reclaimed water distribution systems (RWDSs) poses a threat to water safety. Disinfection is the most common method to control microbial growth. The present study investigated the efficiency and mechanisms of two widely used disinfectants: sodium hypochlorite (NaClO) and chlorine dioxide (ClO₂) on the bacterial community and cell integrity in effluents of RWDSs through high-throughput sequencing (Hiseq) and flow cytometry, respectively. Results showed that a low disinfectant dose (1 mg/L) did not change the bacterial community basically, while an intermediate disinfectant dose (2 mg/L) reduced the biodiversity significantly. However, some tolerant species survived and multiplied in high disinfectant environments (4 mg/L). Additionally, the effect of disinfection on bacterial properties varied between effluents and biofilm, with changes in the abundance, bacterial community, and biodiversity. Results of flow cytometry showed that NaClO disturbed live bacterial cells rapidly, while ClO₂ caused greater damage, stripping the bacterial membrane and exposing the cytoplasm. This research will provide valuable information for assessing the disinfection efficiency, biological stability control, and microbial risk management of reclaimed water supply systems.

Biofilm enhances the copper (II) adsorption on microplastic surfaces in coastal seawater: Simultaneous evidence from visualization and quantification

Microplastics (MPs) exposed to the urban coastal seawater could form biofilms, which facilitate the adsorption and transportation of hazardous contaminants. However, influence of biofilms on the metal adsorption of MPs, especially the co-existence of biofilm and metals on MPs, is still less known. In this study, the adsorption of copper (Cu) on biofilm-coated MPs (BMPs) was visually analyzed and quantified. The results of scanning electron microscopy in combination with energy dispersive X-ray showed that biofilm and metals co-occurred on MPs in seawater. The nanoscale secondary ion mass spectrometry images further exhibited that the distribution of Cu, chlorine (Cl) and biofilm on MP surfaces was highly consistent. Moreover, the adsorption of Cu(II) on BMPs was enhanced as quantified by inductively coupled plasma-mass spectrometer. Furthermore, different species on BMPs with and without Cu were identified, and their potential functions of metal or Cl metabolism were predicted based on KEGG pathway database. Overall, for the first time, this study provides visual and quantified evidences for the enhancement of Cu(II) adsorption on BMPs based on co-localization, and it may shed a light on the development of methodologies for investigating the interaction among MPs, biofilms and pollutants in marine environment.

Occurrence of fungal spores in drinking water: A review of pathogenicity, odor, chlorine resistance and control strategies

Fungi in drinking water have been long neglected due to the lack of convenient analysis methods, widely accepted regulations and efficient control strategies. However, in the last few decades, fungi in drinking water have been widely recognized as opportunity pathogens that cause serious damage to the health of immune-compromised individuals. In drinking water treatment plants, fungal spores are more resistant to chlorine disinfection than bacteria and viruses, which can regrow in drinking water distribution systems and subsequently pose health threats to water consumers. In addition, fungi in drinking water may represent an ignored source of taste and odor (T&O). This review identified 74 genera of fungi isolated from drinking water and presented their detailed taxonomy, sources and biomass levels in drinking water systems. The typical pathways of exposure of water-borne fungi and the main effects on human health are clarified. The fungi producing T&O compounds and their products are summarized. Data on free chlorine or monochloramine inactivation of fungal spores and other pathogens are compared. At the first time, we suggested four chlorine-resistant mechanisms including aggregation to tolerate chlorine, strong cell walls, cellular responses to oxidative stress and antioxidation of melanin, which are instructive for the future fungi control attempts. Finally, the inactivation performance of fungal spores by various technologies are comprehensively analyzed. The purpose of this study is to provide an overview of fungi distribution and risks in drinking water, provide insight into the chlorine resistance mechanisms of fungal spores and propose approaches for the control of fungi in drinking water.

Flow cytometric assessment of the chlorine/chloramine efficacy of particle-associated bacteria in drinking water

Chlorine and chloramine are widely used to maintain the microbial safety after drinking water treatment plants. Particles existing in the treated water may react with these chemical disinfectants, and impact the efficacy of disinfection. However, the protective effects of particles without-disinfectant demand on bacteria in the chlorination/chloramination are not well known. In this study, two laboratory-derived bacteria (Staphylococcus aureus and Escherichia coli) and two no-disinfectant demand particles (Fe₂O₃ and kaolin) in drinking water were selected to build particle-associated bacteria (PAB) systems, and their resistance to chlorine/chloramine was further assessed. Flow cytometry (FCM) was employed to image PAB systems and assess the removal rate of bacteria. The results were that particles showed protective effects on bacteria in half of chlorine experiments and 90% of chloramination. The protection was related to the combination form of particles and bacteria tied to neither particle species nor size, and there was no positive relationship between the protection effect and water turbidity. S. aureus attached to Fe₂O₃ had stronger resistance than kaolin, and kaolin protected E. coli better than Fe₂O₃. The same trend was observed in both chemical disinfectants, and more significant resistance had been shown in chloramination than chlorination. FCM images which gave a qualitative description on the combination states of different PAB systems may be a clue to explain the strength of the resistance. Environmental bacterial strains and particles are recommended in the future to explore practical applications.

A systematic review on chlorine tolerance among bacteria and standardization of their assessment protocol in wastewater

Though chlorine is a cost-effective disinfectant for water and wastewaters, the bacteria surviving after chlorination pose serious public health and environmental problems. This review critically assesses the mechanism of chlorine disinfection as described by various researchers; factors affecting chlorination efficacy; and the re-growth potential of microbial contaminations in treated wastewater post chlorination to arrive at meaningful doses for ensuring health safety. Literature analysis shows procedural inconsistencies in the assessment of chlorine tolerant bacteria, making it extremely difficult to compare the tolerance characteristics of different reported tolerant bacteria. A comparison of logarithmic reduction after chlorination and the concentration-time values for prominent pathogens led to the generation of a standard protocol for the assessment of chlorine tolerance. The factors that need to be critically monitored include applied chlorine doses, contact time, determination of chlorine demands of the medium, and the consideration of bacterial counts immediately after chlorination and in post chlorinated samples (regrowth). The protocol devised here appropriately assesses the chlorine-tolerant bacteria and urges the scientific community to report the regrowth characteristics as well. This would increase the confidence in data interpretation that can provide a better understanding of chlorine tolerance in bacteria and aid in formulating strategies for effective chlorination.

The role of pipe biofilms on dissemination of viral pathogens and virulence factor genes in a full-scale drinking water supply system

Water is an important medium for virus transmission and viral pathogens are increasingly appreciated as a significant water safety issue. However, the effect of pipe biofilms on viral pathogens remains unclear. This research aimed to investigate the dissemination of viruses in a full-scale drinking water supply system (DWSS) and the effect of pipe biofilms on viral pathogens in bulking water. Viral pathogens, pathogenic viral hosts, and viral virulence factors (VFs) were found to disseminate from source water to tap water. The proportion of virus and viral VFs in the biofilm was far less than that in water. The contribution of biofilms in pipe wall to viruses and viral VFs in bulking water was less than 4%, and viruses in the biofilm had no obvious effect on pathogenic viruses in water. Dominant viruses carrying VFs changed from Cyanobacteria virus to Mycobacterium virus after advanced water treatment. Mycobacterium and organics were identified as the key factors influencing composition and abundance of viral VFs, which could explain 41.1% of the variation in viral virulence in the water supply system. Host bacteria and organics may be used as the key targets to control the risk of viruses in DWSSs.

Enhanced photocatalytic activity of Fe2O3@ZnO decorated CQD for inactivation of Escherichia coli under visible light irradiation

The present study, magnetically separable Fe₂O₃@ZnO/CQD nanocomposite was successfully prepared via hydrothermal process and characterized with SEM-EDX, XRD, FTIR, VSM and DRS analysis. The effect of operational parameters includes photocatalyst dosage, photocatalyst type, CQD content and Escherichia coli (E. coli) concentration were evaluated on the E. coli inactivation. The disinfecting ability of nanocomposite components was obtained as Fe₂O₃@ZnO/CQD> Fe₂O₃@ZnO> ZnO> Fe₂O₃> CQD which shows a synergetic effect among different components. The highest E. coli inactivation rate (K_max=0.7606 min^-1) was obtained at photocatalyst dosage of 0.2 g/L and 15% CQD content. The MIC and MBC values value for E. coli were determined 0.1172 mg/mL and 0.4948 respectively that the results tests proved the antibacterial functions of the Fe₂O₃@ZnO/CQD. Nanocomposite showed the high reusability after 4 consecutive cycles, K_max decreased from 0.7606 min^-1 to 0.6181 min^-1. Quenching experiments showed ^•OH and h⁺ are the main reactive oxygen species involved in the E. coli inactivation.

Nontuberculous Mycobacterial Resistance to Antibiotics and Disinfectants: Challenges Still Ahead

The mortality incidence from nontuberculous mycobacteria (NTM) infections has been steadily developing globally. These bacterial agents were once thought to be innocent environmental saprophytic that are only dangerous to patients with defective lungs or the immunosuppressed. Nevertheless, the emergence of highly resistant NTM to different antibiotics and disinfectants increased the importance of these agents in the health system. Currently, NTM frequently infect seemingly immunocompetent individuals at rising rates. This is of concern as the resistant NTM are difficult to control and treat. The details behind this NTM development are only beginning to be clarified. The current study will provide an overview of the most important NTM resistance mechanisms to not only antibiotics but also the most commonly used disinfectants. Such evaluations can open new doors to improving control strategies and reducing the risk of NTM infection. Moreover, further studies are crucial to uncover this association.

Comparison of Macrophage Immune Responses and Metabolic Reprogramming in Smooth and Rough Variant Infections of Mycobacterium mucogenicum

Mycobacterium mucogenicum (Mmuc), a rapidly growing nontuberculous mycobacterium (NTM), can infect humans (posttraumatic wound infections and catheter-related sepsis). Similar to other NTM species, Mmuc exhibits colony morphologies of rough (Mmuc-R) and smooth (Mmuc-S) types. Although there are several case reports on Mmuc infection, no experimental evidence supports that the R-type is more virulent. In addition, the immune response and metabolic reprogramming of Mmuc have not been studied on the basis of morphological characteristics. Thus, a standard ATCC Mmuc strain and two clinical strains were analyzed, and macrophages were generated from mouse bone marrow. Cytokines and cell death were measured by ELISA and FACS, respectively. Mitochondrial respiration and glycolytic changes were measured by XF seahorse. Higher numbers of intracellular bacteria were found in Mmuc-R-infected macrophages than in Mmuc-S-infected macrophages. Additionally, Mmuc-R induced higher levels of the cytokines TNF-α, IL-6, IL-12p40, and IL-10 and induced more BMDM necrotic death. Furthermore, our metabolic data showed marked glycolytic and respiratory differences between the control and each type of Mmuc infection, and changes in these parameters significantly promoted glucose metabolism, extracellular acidification, and oxygen consumption in BMDMs. In conclusion, at least in the strains we tested, Mmuc-R is more virulent, induces a stronger immune response, and shifts bioenergetic metabolism more extensively than the S-type. This study is the first to report differential immune responses and metabolic reprogramming after Mmuc infection and might provide a fundamental basis for additional studies on Mmuc pathogenesis.

Chlorine Tolerance and Cross-Resistance to Antibiotics in Poultry-Associated Salmonella Isolates in China

Chlorine disinfectants have been widely used in the poultry supply chain but this exposure can also result in the development of bacterial tolerance to chlorine and this is often linked to antibiotic cross-resistance. The objectives of this study were to investigate sodium hypochlorite (NaClO) tolerance of Salmonella isolated from poultry supply chains and evaluate cross-resistance. We collected 172 Salmonella isolates from poultry farms, slaughter houses and retail markets in China during 2019–2020. We found that S. Enteritidis, S. Kentucky, and S. Typhimurium constituted > 80% of our Salmonella isolates. Overall, 68% of Salmonella isolates were resistant to > 3 antibiotics and S. Kentucky displayed a significantly (p > 0.05) higher frequency (93.2%) of multidrug resistance than the other serovars. Tolerance to chlorine at MIC > 256 mg/L was detected in 93.6% of isolates (161/172) and tolerant isolates displayed higher decimal reduction times (D value) and less ultrastructural damage than did the suspectable strains under chlorine stress. Spearman analysis indicated significant positive correlations between chlorine tolerance (evaluated by the OD method) and antibiotic resistance (p < 0.05) to ceftiofur, tetracycline, ciprofloxacin and florfenicol and this was most likely due to efflux pump over-expression. The most frequently detected chlorine resistance gene was qacEΔ1 (83.1%, n = 143) and we found a positive correlation between its presence and MIC levels (r = 0.66, p < 0.0001). Besides, we found weak correlations between chlorine-tolerance and antibiotic resistance genes. Our study indicated that chlorine disinfectants most likely played an important role in the emergence of chlorine tolerance and spread of antibiotic resistance and therefore does not completely control the risk of food-borne disease. The issue of disinfectant resistance should be examined in more detail at the level of the poultry production chain.

The source and fate of Mycobacterium tuberculosis complex in wastewater and possible routes of transmission

BACKGROUND

The Mycobacterium tuberculosis complex (MTBC) consists of causative agents of both human and animal tuberculosis and is responsible for over 10 million annual infections globally. Infections occur mainly through airborne transmission, however, there are possible indirect transmissions through a faecal-oral route which is poorly reported. This faecal-oral transmission could be through the occurrence of the microbe in environments such as wastewater. This manuscript, therefore, reviews the source and fate of MTBC in the wastewater environment, including the current methods in use and the possible risks of infections.

RESULTS

The reviewed literature indicates that about 20% of patients with pulmonary TB may have extra-pulmonary manifestations such as GITB, resulting in shedding in feaces and urine. This could potentially be the reason for the detection of MTBC in wastewater. MTBC concentrations of up to 5.5 × 105 (±3.9 × 105) copies/L of untreated wastewater have been reported. Studies have indicated that wastewater may provide these bacteria with the required nutrients for their growth and could potentially result in environmental transmission. However, 98.6 (± 2.7) %, removal during wastewater treatment, through physical-chemical decantation (primary treatment) and biofiltration (secondary treatment) has been reported. Despite these reports, several studies observed the presence of MTBC in treated wastewater via both culture-dependent and molecular techniques.

CONCLUSION

The detection of viable MTBC cells in either treated or untreated wastewater, highlights the potential risks of infection for wastewater workers and communities close to these wastewater treatment plants. The generation of aerosols during wastewater treatment could be the main route of transmission. Additionally, direct exposure to the wastewater containing MTBC could potentially contribute to indirect transmissions which may lead to pulmonary or extra-pulmonary infections. This calls for the implementation of risk reduction measures aimed at protecting the exposed populations.

Synergistic effect of ozone and chlorine on inactivating fungal spores: Influencing factors and mechanisms

Effective control of fungal contamination in water is vital to provide healthy and safe drinking water for human beings. Although ozone was highly effective in inactivating fungi in water, it was limited by a lack of continuous disinfection ability in water supply system. In present study, the inactivation of fungal spores by combining ozone and chlorine was investigated. The synergistic effects of Aspergillus niger and Trichoderma harzianum spores reached 0.47- and 0.55-log within 10 min, respectively. The inactivation efficiency and the synergistic effect would be affected by disinfectant concentration, pH, and temperature. The combined inactivation caused more violent oxidative stimulation and more severe damage to the fungal spores than the individual inactivation based on the flow cytometry analysis and the scanning electron microscopy observation. The synergistic effect during the combined inactivation process was attributed to the generation of hydroxyl radicals by the reaction between ozone and chlorine and the promotion of chlorine penetration by the destruction of cell wall by ozone. The combined inactivation efficiency in natural water samples was reduced by 26.4-43.8% compared with that in PBS. The results of this study provided an efficient and feasible disinfection method for the control of fungi in drinking water.

Evaluation of Structural Changes and Molecular Mechanism Induced by High Hydrostatic Pressure in Enterobacter sakazakii

The contamination of infant milk and powder with Enterobacter sakazakii poses a risk to human health and frequently caused recalls of affected products. This study aims to explore the inactivation mechanism of E. sakazakii induced by high hydrostatic pressure (HHP), which, unlike conventional heat treatment, is a nonthermal technique for pasteurization and sterilization of dairy food without deleterious effects. The mortality of E. sakazakii under minimum reaction conditions (50 MPa) was 1.42%, which was increased to 33.12% under significant reaction conditions (400 MPa). Scanning electron microscopy (SEM) and fluorescent staining results showed that 400 MPa led to a loss of physical integrity of cell membranes as manifested by more intracellular leakage of nucleic acid, intracellular protein and K⁺. Real-time quantitative PCR (RT-qPCR) analysis presents a downregulation of three functional genes (glpK, pbpC, and ompR), which were involved in cell membrane formation, indicating a lower level of glycerol utilization, outer membrane protein assembly, and environmental tolerance. In addition, the exposure of E. sakazakii to HHP modified oxidative stress, as reflected by the high activity of catalase and super oxide dismutase. The HHP treatment lowered down the gene expression of flagellar proteins (fliC, flgI, fliH, and flgK) and inhibited biofilm formation. These results determined the association of genotype to phenotype in E. sakazakii induced by HHP, which was used for the control of food-borne pathogens.

Both viable and inactivated amoeba spores protect their intracellular bacteria from drinking water disinfection

In drinking water systems, waterborne pathogens constitute a significant threat. While most studies focus on a single infectious agent, such as bacteria, fungi, viruses, and protists, the effect of interactions among these infectious agents on disinfection treatment has largely been ignored. In this study, we find that dormant amoeba spores, a frequently found protist in drinking water systems, can protect their intracellular bacteria from drinking water disinfection. Bacteria-containing amoeba spores were constructed and treated with various disinfection techniques (Cl₂, ClO_2, and UV₂₅₄). The three disinfection methods could kill the bacteria alone efficiently (6-log inactivation). However, the inactivation efficiency of bacteria that hid within amoeba spore was significantly inhibited (2-3-log inactivation). We also found that inactivated amoeba spores can still protect their intracellular bacteria. This study provides direct evidence that viable and inactivated amoeba spores can protect their hitchhiking bacteria from disinfection treatment, which is crucial for future decision-making about the dosage for sufficient bacterial disinfection in drinking water systems.

Effect of ultraviolet disinfection on the fouling of reverse osmosis membranes for municipal wastewater reclamation

Membrane fouling is a prominent problem that hinders the stable and efficient operation of the reverse osmosis (RO) system for wastewater reclamation. Previous studies showed that chlorine disinfection, which was commonly used in industrial RO systems as pretreatment, could lead to significant change in microbial community structure and resulted in serious biofouling. In order to prevent biofouling during wastewater reclamation, the effect of ultraviolet (UV) disinfection on RO membrane fouling was investigated and the mechanism was also revealed in this study. With the disinfection pretreatment by UV of 20, 40 and 80 mJ/cm², the bacteria in the feed water were inactivated significantly with a log reduction of 1.11, 2.55 and 3.61-log, respectively. However, RO membrane fouling aggravated with higher UV dosage. Especially, in the group with the UV dosage of 80 mJ/cm², the normalized RO membrane flux decreased by 15% compared with the control group after 19-day operation. The morphology of the fouled RO membranes indicated serious biofouling in all groups. The analysis on the microbial amount of the foulants showed that the heterotrophic plate counts (HPC) and ATP content on the fouled RO membranes with and without UV disinfection were at the same level. However, the total organic carbon content of the foulants with the UV dosage of 40 and 80 mJ/cm² was significantly higher than the control group, with higher content of proteins and polysaccharides as indicated by EEM and FTIR spectrum. Microbial community structure analysis showed that some typical UV-resistant bacteria were selected and remained on the RO membrane after disinfection with high UV dosage, including. These residual bacteria after disinfection with high UV dosage showed higher extracellular polymeric substances (EPS) secretion compared with those without UV disinfection, and thus aggravated RO membrane fouling. Thicker EPS could decrease the transmission of UV rays, and thus bacteria with higher EPS secretion might be selected after UV disinfection.

Disinfectant resistance in bacteria: Mechanisms, spread, and resolution strategies

Disinfectants are widely acknowledged for removing microorganisms from the surface of the objects and transmission media. However, the emergence of disinfectant resistance has become a severe threat to the safety of life and health and the rational allocation of resources due to the reduced disinfectant effectiveness. The horizontal gene transfer (HGT) of disinfectant resistance genes has also expanded the resistant flora, making the situation worse. This review focused on the resistance mechanisms of disinfectant resistant bacteria on biofilms, cell membrane permeability, efflux pumps, degradable enzymes, and disinfectant targets. Efflux can be the fastest and most effective resistance mechanism for bacteria to respond to stress. The qac genes, located on some plasmids which can transmit resistance through conjugative transfer, are the most commonly reported in the study of disinfectant resistance genes. Whether the qac genes can be transferred through transformation or transduction is still unclear. Studying the factors affecting the resistance of bacteria to disinfectants can find breakthrough methods to more adequately deal with the problem of reduced disinfectant effectiveness. It has been confirmed that the interaction of probiotics and bacteria or the addition of 4-oxazolidinone can inhibit the formation of biofilms. Chemicals such as eugenol and indole derivatives can increase bacterial sensitivity by reducing the expression of efflux pumps. The role of these findings in anti-disinfectant resistance has proved invaluable.

Global bibliometric meta-analytic assessment of research trends on microbial chlorine resistance in drinking water/water treatment systems

Chlorine is the commonest and cheapest disinfectant used in drinking water and wastewater treatment at household, municipal and industrial levels. However, the uprising of microbial chlorine resistance (MCR) pose critical public health hazard concerns; because, its potentiate exposure to difficult-to-treat resistant pathogens. Therefore, this study aimed at evaluating the burden of MCR in drinking water/wastewater treatment and distribution systems (DWWTDS) via science mapping of research productivity (authors, countries, institutions), thematic conceptual framework, disciplines, research networks and associated intellectual landscape. MCR data were mined from Scopus and Web of Science based on optimized algorithms with the root key term "chlorine* resistant*'' and analysed for pre-set indicator variables. Results revealed 1127 documents from 442 journals and 1430% average growth rate (AGR) of research articles from 2017 to 2019 on MCR. Country-wise, the USA (n = 299), China (n = 119), and Japan (n = 43) ranked in the 1st, 2nd, and 3rd positions respectively, among the top participating countries in MCR research. MCR research had considerable performance in public health and sustainable concern subjects namely, Environmental Sciences & Ecology, Engineering, Microbiology, Water Resources, Biotechnology & Applied Microbiology, Food Science & Technology, Public, Environ & Occupational Health, Chemistry, Infectious Diseases, and Marine & Freshwater Biology; and with noticeable AGR in Environmental Sciences & Ecology (330%) and Infectious Diseases (130%). The study found biofilm-related thrusts (n = 90, 270% AGR) as main research hotspots on MCR. Overall, the study identified and discussed four important thematic areas of public health challenges in MCR that could promote increasing waterborne diseases due to (re)emerging pathogens, enteric viruses and dissemination in DWWTDS. In conclusion, this study provides comprehensive overview of the growing burden of MCR in DWWTDS and standout as a primer of information for researchers on MCR. It recommends direct, intentional and integrated research priorities on MCR to overcome accompanying public health and environmental threats. In addition, chlorine resistance in waterborne fungi have not received research attention. Research activities related to fungal chlorine resistance will be an invaluable future direction in DWWTDS and guide against exposure to waterborne pathogenic fungi and mycotoxins. It is unknown whether chlorine resistance can be acquired by horizontal gene transfer in microorganisms and future research should elucidate this important thrust.

The virus removal in UV irradiation, ozonation and chlorination

The COVID-19 pandemic draws much attention to virus inactivation since the SARS-CoV-2 was detected in miscellaneous environments and the wastewater can be a potential transmitting pathway. UV irradiation, ozonation and chlorination are widely used disinfection processes in water treatment. In this review, the mechanisms and applications of three disinfection processes are introduced, and their inactivation effects on virus as well as other microorganisms are compared and discussed. The resistance of viruses to UV irradiation is generally stronger than that of bacteria. 4-log inactivation of bacteria can be easily obtained within a UV dose of 10 ​mJ/cm². However, the doses to reach the same virus removal rate vary greatly from 10 to 140 ​mJ/cm². The coronaviruses have even stronger UV resistance. Comparatively, ozonation and chlorination are effective methods to inactivate viruses, and the CT values of 4-log removal for most viruses concerned are lower than 1 ​mg·min/L and 10 ​mg·min/L, respectively. Protozoa, fungal spores and bacterial spores are more resistant to disinfection. Temperature, pH, organic matters, turbidity and other parameters all have influences on the disinfection. With a 10 ​°C decrease in temperature, the CT value required for certain removal rates doubles. Generally low pH promotes disinfection and high pH is against it. In drinking water and wastewater treatment process, the resistance properties of microorganisms and other influence parameters should be taken into consideration when choosing disinfection technologies.

Evaluating method and potential risks of chlorine-resistant bacteria (CRB): A review

Chlorine-resistant bacteria (CRB) are commonly defined as bacteria with high resistance to chlorine disinfection or bacteria which can survive or even regrow in the residual chlorine. Chlorine disinfection cannot completely control the risks of CRB, such as risks of pathogenicity, antibiotic resistance and microbial growth. Currently, researchers pay more attention to CRB with pathogenicity or antibiotic resistance. The microbial growth risks of non-pathogenic CRB in water treatment and reclamation systems have been neglected to some extent. In this review, these three kinds of risks are all analyzed, and the last one is also highlighted. In order to study CRB, various methods are used to evaluate chlorine resistance. This review summarizes the evaluating methods for chlorine resistance reported in the literatures, and collects the important information about the typical isolated CRB strains including their genera, sources and levels of chlorine resistance. To our knowledge, few review papers have provided such systematic information about CRB. Among 44 typical CRB strains from 17 genera isolated by researchers, Mycobacterium, Bacillus, Legionella, Pseudomonas and Sphingomonas were the five genera with the highest frequency of occurrence in literatures. They are all pathogenic or opportunistic pathogenic bacteria. In addition, although there are many studies on CRB, information about chlorine resistance level is still limited to specie level or strain level. The difference in chlorine resistance level among different bacterial genera is less well understood. An inconvenient truth is that there is still no widely-accepted method to evaluate chlorine resistance and to identify CRB. Due to the lack of a unified method, it is difficult to compare the results about chlorine resistance level of bacterial strains in different literatures. A recommended evaluating method using logarithmic removal rate as an index and E. coli as a reference strain is proposed in this review based on the summary of the current evaluating methods. This method can provide common range of chlorine resistance of each genus and it is conducive to analyzing the distribution and abundance of CRB in the environment.

Identification and inactivation of Gordonia, a new chlorine-resistant bacterium isolated from a drinking water distribution system

Chlorine-resistant bacteria threaten drinking water safety in water distribution systems. In this study, a novel chlorine-resistant bacterium identified as Gordonia was isolated from the drinking water supply system of Jinan City for the first time. We examined the resistance and inactivation of the isolate by investigating cell survival, changes in cell morphology, and the permeability of cell membranes exposed to chlorine. After 240 min chlorine exposure, the chlorine residual was greater than 0.5 mg L^-1 and the final inactivation was about 3 log reduction, which showed that the Gordonia strain had high chlorine tolerance. Flow-cytometric analysis indicated that, following sodium hypochlorite treatments with increasing membrane permeability, culturable cells enter a viable but nonculturable state and then die. We also investigated the inactivation kinetics of Gordonia following chlorine dioxide and ultraviolet radiation treatment. We found that these treatments can effectively inactivate Gordonia, which suggests that they may be used for the regulation of chlorine-resistant microorganisms.

Efficient inactivation of bacteria in ballast water by adding potassium peroxymonosulfate alone: Role of halide ions

In recent years, ballast water disinfection has been paid much more attention due to the untreated discharged ballast water posing threaten of biological invasion and health related consequences. In this study, an effective and simple approach for ballast water disinfection by just adding potassium peroxymonosulfate (PMS) was assessed, and the role of halide ions in seawater on the enhancement of inactivation was revealed. The reactive species responsible for inactivation, the leakage of intracellular materials, and changes of cellular morphology after inactivation were evaluated to explore the inactivation mechanism. The results showed that Escherichia coli and Bacillus subtilis in ballast water could be totally inactivated within 10 min by adding 0.2 mM PMS alone. The inactivation of bacteria in ballast water fitted to the delayed Chick-Watson model. Chloride and bromide ion in seawater were found to play a crucial role in inactivating bacteria, while the effect of iodide ion could be negligible due to its relative lower concentration in seawater. Chlorine and bromine, produced by the reaction of PMS with chloride and bromide ion, were proved to be the main reactive components that were responsible for the inactivation of bacteria. The extracellular ATP and total nitrogen concentration increased after inactivation which indicated that cell membrane was destroyed by reactive oxidants produced by the reaction between PMS and halide ions. The change of cell morphology confirmed that bacteria were seriously damaged after inactivation. The results suggest that PMS is an attractive alternative disinfectant for ballast water disinfection and this application deserved further research.

Inactivation of antibiotic resistant Escherichia coli and degradation of its resistance genes by glow discharge plasma in an aqueous solution

Emerging contaminants such as antibiotic resistance bacteria (ARB) and antibiotic resistance genes (ARGs) are becoming a global environmental problem. In this study, the glow discharge plasma (GDP) was applied for degrading antibiotic resistant Escherichia coli (E. coli) with resistance genes (tetA, tetR, aphA) and transposase gene (tnpA) in 0.9% sterile saline. The results showed that GDP was able to inactivate the antibiotic resistant E. coli and remove the ARGs and reduce the risk of gene transfer. The levels of E. coli determined by 16S rRNA decreased by approximately 4.7 logs with 15 min of discharge treatment. Propidium monoazide - quantitative polymerase chain reaction (PMA-qPCR) tests demonstrated that the cellular structure of 4.8 more logs E. coli was destroyed in 15 min. The reduction of tetA, tetR, aphA, tnpA genes was increased to 5.8, 5.4, 5.3 and 5.5 logs with 30 min discharge treatment, respectively. The removal of ARGs from high salinity wastewater was also investigated. The total abundance of ARGs was reduced by 3.9 logs in 30 min. Scavenging tests indicated that hydroxyl radicals (·OH) was the most probable agents for bacteria inactivation and ARGs degradation. In addition, the active chlorine (Cl· and Cl₂) which formed during the discharge may also contribute to the inactivation and degradation.

Comparison of different disinfection processes for controlling disinfection by-product formation in rainwater

With increasing shortage of clean water, rainwater has been considered as a precious alternative drinking water source. The processes applied to rainwater treatment are responsible for the safety of drinking water. Therefore, we systematically compared different disinfection processes to evaluate the control of disinfection by-product (DBP) formation and integrated cyto- and genotoxicity of the treated rainwater for the first time. The evaluated disinfection processes included chlorination and chloramination, pre-oxidation by potassium permanganate (KMnO₄) and potassium ferrate (K₂FeO₄), ultraviolet/hydrogen peroxide (UV/H₂O₂), and ultraviolet/persulfate (UV/PS) processes. The results revealed that chloramination was effective for controlling the formation of carbonaceous DBPs (C-DBPs), but not nitrogenous DBPs (N-DBPs). Compared to KMnO₄ pre-oxidation, better reduction of almost all DBPs was observed during K₂FeO₄ pre-oxidation. According to the calculation of cytotoxicity index (CTI) and genotoxicity index (GTI), cyto- and genotoxicity of the samples decreased obviously at the dosage of ≥ 2.0 mg/L KMnO₄ and K₂FeO₄. The control of the cyto- and genotoxicity of the formed DBPs from the two UV-related AOPs was more effective at the dosage of ≥ 1.0 mM PS and ≥ 5.0 mM H₂O₂. Moreover, UV/PS was much more powerful to alter the structure of DBP precursors in rainwater.

The effects of ultraviolet disinfection on vancomycin-resistant Enterococcus faecalis

The emergence of vancomycin-resistant Enterococcus faecalis (E. faecalis) in water is threatening the health of human beings. The effect of ultraviolet disinfection on vancomycin-resistant E. faecalis, including the effectiveness, photoreactivation and dark repair of E. faecalis, and the deactivation mechanism were investigated in this work. Ultraviolet disinfection could quickly inactivate the target antibiotic resistant bacterium (ARB), E. faecalis, and it caused damage to the cell membrane and induced the decrease of the total adenosine triphosphate (ATP) content and the superoxide dismutase (SOD) activity significantly (p < 0.05). E. faecalis could reactivate after ultraviolet disinfection especially under light conditions. Furthermore, the removal of the selected antibiotic resistance gene (ARG), vanB, by ultraviolet radiation and the effect on the vancomycin resistance of E. faecalis were investigated, which showed that ultraviolet disinfection had no significant effect on the vancomycin resistance of E. faecalis (p > 0.05).

Antibacterial performance of polymer quaternary ammonium salt-capped silver nanoparticles on Bacillus subtilis in water

In this study, we prepared polymer quaternary ammonium salt–capped silver nanoparticles (PQAS–AgNPs) and investigated their antimicrobial activities. The antimicrobial effectiveness of PQAS–AgNPs on Bacillus subtilis (B. subtilis), and the effect of dose, pH, chloride ion and humic acid (HA) were studied. It was found that PQAS–AgNPs revealed excellent antimicrobial activity to B. subtilis, compared with polyvinylpyrrolidone-capped silver nanoparticles (PVP-AgNPs), which was the reference antimicrobial material. The positive surface, the antimicrobial activity of PQAS, and the synergistic antibacterial effect between PQAS and AgNPs contributed to the significant antibacterial superiority of PQAS–AgNPs. This study demonstrated that the impact of the dose of the material was positive and the microbiocidal efficacy of PQAS–AgNPs was stronger at lower pH. In addition, the antibacterial performance of PQAS–AgNPs decreased in the presence of Cl⁻ and HA. Finally, in combination with the results of FCM and adenosine triphosphate (ATP) content, it was found that PQAS–AgNPs destroyed the respiratory chain of bacterial cells, reduced the synthesis of ATP, and destroyed the cell wall and cell membrane function.

Polymer quaternary ammonium salt–capped silver nanoparticles (PQAS–AgNPs) were synthesized, and they exhibited significant antibacterial capacity against Bacillus subtilis.

Nontuberculous mycobacteria in drinking water systems - the challenges of characterization and risk mitigation

Nontuberculous mycobacteria (NTM) pulmonary infections are a growing concern worldwide, with a disproportionate incidence in persons with pre-existing health conditions. NTM have frequently been found in municipally-treated drinking water and building plumbing, leading to the hypothesis that an important source of NTM exposure is drinking water. The identification and quantification of NTM in environmental samples are complicated by genetic variability among NTM species, making it challenging to determine if clinically relevant NTM are present. Additionally, their unique cellular features and lifestyles make NTM and their nucleic acids difficult to recover. This review highlights a recent work focused on quantification and characterization of NTM and on understanding the influence of source water, treatment plants, distribution systems, and building plumbing on the abundance of NTM in drinking water.