Induction of Escherichia coli into a VBNC state through chlorination/chloramination and differences in characteristics of the bacterium between states

Resting for viability: Gordonia polyisoprenivorans ZM27, a robust generalist for petroleum bioremediation under hypersaline stress

The intrinsic issue associated with the application of microbes for practical pollution remediation involves maintaining the expected activity of engaged strains or consortiums as effectively as that noted under laboratory conditions. Faced with various stress factors, degraders with dormancy ability are more likely to survive and exhibit degradation activity. In this study, a hydrocarbonoclastic and halotolerant strain, Gordonia polyisoprenivorans ZM27, was isolated via stimulation with resuscitation-promoting factor (Rpf). Long-term exposure to dual stresses of 10% NaCl and starvation induced ZM27 to enter a viable but nonculturable (VBNC)-like state, and ZM27 cells could be resuscitated upon Rpf stimulation. Notable changes in both morphological and physiological characteristics between VBNC-like ZM27 cells and resuscitated cells confirmed the response to Rpf and their robust resistance against harsh environments. Whole-genome sequencing and analysis indicated ZM27 could be a generalist degrader with dormancy ability. Subsequently, VBNC-like ZM27 was applied in a soil microcosm experiment to investigate the practical application potential under harsh conditions. VBNC-like ZM27 combined with Rpf stimulation exhibited the most effective biodegradation performance, and the initial n-hexadecane content (1000 mg kg-1) decreased by 63.29% after 14-day incubation. Based on 16S rRNA amplicon sequencing and analysis, Gordonia exhibited a positive response to Rpf stimulation. The relative abundance of genus Gordonia was negatively correlated with that of Alcanivorax, a genus of obligate hydrocarbon degrader with the greatest abundance during soil incubation. Based on the degradation profile and community analysis, generalist Gordonia may be more efficient in hydrocarbon degradation than specialist Alcanivorax under harsh conditions. The characteristics of ZM27, including its sustainable culturability under long-term stress, response to Rpf and robust performance in soil microcosms, are valuable for the remediation of petroleum pollution under stressful conditions. Our work validated the importance of dormancy and highlighted the underestimated role of low-activity degraders in petroleum remediation.

The viable but non-culturable (VBNC) status of Shewanella putrefaciens (S. putrefaciens) with thermosonication (TS) treatment

Although thermosonication (TS) treatment has been widely used in food sterilization, the viable but non-culturable (VBNC) of bacteria with TS treatment has still concerned potential food safety and public health. The molecular mechanism of VBNC status of bacteria with TS treatment is not clearly known. Therefore, in this study, we used Shewanella putrefaciens, which was a common putrefactive bacteria in aquatic products, to study the VBNC state of bacteria with TS treatment. Firstly, our results revealed that S. putrefaciens still could enter the VBNC state after TS treatments: 50 kHz, 300 W, 30 min ultrasonic treatment and 70 °C heating; Subsequently, we found the VBNC state of S. putrefaciens can resist the damage of TS treatment, such as cell wall break, DNA degradation, etc; Finally, four-dimensional data-independent acquisition-based proteomics showed that under VBNC state, S. putrefaciens upregulated functional proteins to resist TS treatment, such as: ribosomal proteins to accelerate the synthesis of stress proteins to counteract TS treatments, ornithine decarboxylase SpeF and MraY to repair TS treatment-induced damage, etc. Meanwhile, S. putrefaciens downregulates metabolic and transport functional proteins such as dehydrogenase to reduce the metabolism. Importantly, among those proteins, the ribosomal transcriptional regulatory protein family, such as rpsB, etc, may be the key proteins for S. putrefaciens entering VBNC state. This finding can provide some new strategies for preventing VBNC status of bacteria with TS treatment, such as: inhibition of key proteins, etc.

Copper single-atom catalysts for broad-spectrum antibiotic-resistant bacteria (ARBs) antimicrobial: Activation of peroxides and mechanism of ARBs inactivation

Antibiotic-resistant bacteria (ARBs) have been widely detected in wastewater and become a potential threat to human health. This work found that low-load single-atom copper (0.1 wt%) anchored on g-C3N4 (SA-Cu/g-C3N4) exhibited excellent ability to activate H2O2 and inactivate ARBs during the photo-Fenton process. The presence of SA-Cu/g-C3N4 (0.4 mg/mL) and H2O2 (0.1 mM) effectively inactivated ARBs. More than 99.9999 % (6-log) of methicillin-resistant Staphylococcus aureus (MRSA), and carbapenem-resistant Acinetobacter baumannii (CRAB) could be inactivated within 5 min. Extended-spectrum β-lactamase-producing pathogenic Escherichia coli (ESBL-E) and vancomycin-resistant Enterococcus faecium (VRE) were killed within 10 and 30 min, respectively. In addition, more than 5-log of these ARBs were killed within 60 min in real wastewater. Furthermore, D2O-labeling with Raman spectroscopy revealed that SA-Cu/g-C3N4 completely suppressed the viable but nonculturable (VBNC) state and reactivation of bacteria. Electron paramagnetic resonance spectroscopy results demonstrated that g-C3N4 mainly produced 1O2, while SA-Cu/g-C3N4 simultaneously produced both 1O2 and •OH. The •OH and 1O2 cause lipid peroxidation damage to the cell membrane, resulting in the death of the bacteria. These findings highlight that the SA-Cu/g-C3N4 catalyst is a promising photo-Fenton catalyst for the inactivation of ARBs in wastewater.

Viable but non-culturable state formation and resuscitation of different antibiotic-resistant Escherichia coli induced by UV/chlorine

The presence of "viable but nonculturable" (VBNC) state and bacterial antibiotic resistance (BAR) both pose significant threats to the safety of drinking water. However, limited data was available that explicitly addressed the contribution of bacterial VBNC state in the maintenance and propagation of BAR. Here, the VBNC state induction and resuscitation of two antibiotic-resistant Escherichia coli K12 strains, one carrying multidrug-resistant plasmid (RP4 E. coli) and the other with chromosomal mutation (RIF E. coli) were characterized by subjecting them to different doses of UV/chlorine. The results illustrated that the induction, resuscitation, and associated mechanisms of VBNC ARB exhibit variations based on resistance determinants. RP4 E. coli exhibited a higher susceptibility to enter VBNC state compared to the RIF E. coli., and most VBNC state and resuscitated RP4 E. coli retained original antibiotic resistance. While, reverse mutation in the rpoB gene was observed in VBNC state and recovered RIF E. coli strains induced by high doses of UV/chlorine treatment, leading to the loss of rifampicin resistance. According to RT-qPCR results, ARGs conferring efflux pumps appeared to play a more significant role in the VBNC state formation of RP4 E. coli and the down-regulation of rpoS gene enhanced the speed at which this plasmid-carrying ARB entered into the dormant state. As to RIF E. coli, the induction of VBNC state was supposed to be regulated by the combination of general stress response, SOS response, stringent response, and TA system. Above all, this study highlights that ARB could become VBNC state during UV/chlorine treatments and retain, in some cases, their ability to spread ARGs. Importantly, compared with chromosomal mutation-mediated ARB, both VBNC and resuscitated state ARB that carries multidrug-resistant plasmids poses more serious health risks. Our study provides insights into the relationship between the VBNC state and the propagation of BAR in drinking water systems.

Acanthamoebae as a protective reservoir for Pseudomonas aeruginosa in a clinical environment

BACKGROUND

Pseudomonas aeruginosa is a growing concern in healthcare-associated infections and poses significant risk to those with serious underlying health conditions. The antimicrobial resistance traits of the pathogen and ability to form biofilms make effective mitigation and disinfection strategies difficult. Added to this challenge is the role that free-living amoebae such as Acanthamoeba play in the detection, disinfection and transmission of P. aeruginosa. P. aeruginosa can survive intracellularly within amoebae, which has the potential to limit detectability and permit transmission into high-risk areas.

METHODS/FINDINGS

We screened for the presence of Acanthamoeba spp. and P. aeruginosa within a functioning general hospital in Scotland using a culture and molecular approach, noting their presence at several sites over a four-month period, particularly within floor drains connecting patient rooms. In addition, microbiome analysis revealed that amoebae harbour a unique microbial community comprised primarily of Pseudomonas spp. that were not readily detected using microbiome sequencing techniques on environmental swabs. Having demonstrated that both organisms were consistently present in hospital settings, we investigated the relationship between acanthamoeba and P. aeruginosa in the laboratory, showing that (i) acanthamoeba growth rate is increased in the presence of pseudomonas biofilms and viable pseudomonas persist within the amoebae and (ii) hydrogen peroxide-based disinfectants are significantly less effective against an isolate of P. aeruginosa in the presence of acanthamoeba than when the bacteria are incubated alone.

CONCLUSIONS

These findings suggest that amoebae, and other protists, can influence the detection and persistence of P. aeruginosa in high-risk areas and should be considered when implementing mitigation strategies.

Efficient disinfection of combined sewer overflows by ultraviolet/peracetic acid through intracellular oxidation with preserving cell integrity

Combined sewer overflows (CSOs) introduce microbial contaminants into the receiving water bodies, thereby posing risks to public health. This study systematically investigated the disinfection performance and mechanisms of the combined process of ultraviolet and peracetic acid (UV/PAA) in CSOs with selecting Escherichia coli (E. coli) as a target microbial contaminant. The UV/PAA process exhibited superior performance in inactivating E. coli in simulated CSOs compared with UV, PAA, and UV/H2O2 processes. Increasing the PAA dosage greatly enhanced the disinfection efficiency, while turbidity and organic matter hindered the inactivation performance. Singlet oxygen (1O2), hydroxyl (•OH) and organic radicals (RO•) contributed to the inactivation of E. coli, with •OH and RO• playing the prominent role. Variations of intracellular reactive oxygen species, malondialdehyde, enzymes activities, DNA contents and biochemical compositions of E. coli cells suggested that UV/PAA primarily caused oxidative damage to intracellular molecules rather than the damage to the lipids of the cell membrane, therefore effectively limited the regrowth of E. coli. Additionally, the UV/PAA process displayed an outstanding performance in disinfecting actual raw CSOs, achieving a 2.90-log inactivation of total bacteria after reaction for 4 min. These results highlighted the practical applicability and effectiveness of the UV/PAA process in the disinfection of CSOs.

Fluid flow drives phenotypic heterogeneity in bacterial growth and adhesion on surfaces

Bacteria often thrive in surface-attached communities, where they can form biofilms affording them multiple advantages. In this sessile form, fluid flow is a key component of their environments, renewing nutrients and transporting metabolic products and signaling molecules. It also controls colonization patterns and growth rates on surfaces, through bacteria transport, attachment and detachment. However, the current understanding of bacterial growth on surfaces neglects the possibility that bacteria may modulate their division behavior as a response to flow. Here, we employed single-cell imaging in microfluidic experiments to demonstrate that attached Escherichia coli cells can enter a growth arrest state while simultaneously enhancing their adhesion underflow. Despite utilizing clonal populations, we observed a non-uniform response characterized by bistable dynamics, with co-existing subpopulations of non-dividing and actively dividing bacteria. As the proportion of non-dividing bacteria increased with the applied flow rate, it resulted in a reduction in the average growth rate of bacterial populations on flow-exposed surfaces. Dividing bacteria exhibited asymmetric attachment, whereas non-dividing counterparts adhered to the surface via both cell poles. Hence, this phenotypic diversity allows bacterial colonies to combine enhanced attachment with sustained growth, although at a reduced rate, which may be a significant advantage in fluctuating flow conditions.

Solar/ClO2 system inactivates fungal spores in drinking water: Synergy, efficiency and mechanisms

The risk of fungal pollution in drinking water has been paid attention. Solar/chlorine dioxide (ClO2) combined system is an environment-friendly, economical and efficient disinfection method, especially for countries and regions that are economically backward and still exposed to unsafe drinking water. In this paper, the kinetics, influencing factors, mechanism and regrowth potential of inactivated Aspergillus niger (A. niger) spores by solar/ClO2 were reported for the first time. The inactivation curve can be divided into three stages: instant inactivation within 1-2 min, slow linear inactivation and finally a tail. The synergistic factors produced by solar/ClO2 in terms of log reduction and maximum inactivation rate were 1.194 and 1.112, respectively. The inhibitory effect on the regrowth of A. niger spores inactivated by solar/ClO2 was also stronger than that by ClO2 alone. Strongly oxidizing reactive species produced by solar/ClO2 accelerated the accumulation of endogenic reactive oxygen species (ROS) caused by oxidation stress of A. niger spores, improving the inactivation ability of the system. The inactivation order of A. niger spores was: loss of culturability, accumulation of intracellular ROS, loss of membrane integrity, leakage of intracellular species and change of morphology. The inactivation performance of solar/ClO2 was better than solar/chlor(am)ine according to the comparison of inactivation efficiency and regrowth potential. Results also suggested that solar/ClO2 process was more suitable for the treatment of ground water sources.

Nanowire-assisted electroporation via inducing cell destruction for inhibiting formation of VBNC bacteria: Comparison with chlorination

The induction of viable but nonculturable (VBNC) bacteria with cellular integrity and low metabolic activity by chemical disinfection causes a significant underestimation of potential microbiological risks in drinking water. Herein, a physical Co3O4 nanowire-assisted electroporation (NW-EP) was developed to induce cell damage via the locally enhanced electric field over nanowire tips, potentially achieving effective inhibition of VBNC cells as compared with chemical chlorination (Cl2). NW-EP enabled over 5-log removal of culturable cell for various G+/G- bacteria under voltage of 1.0 V and hydraulic retention time of 180 s, and with ∼3-6 times lower energy consumption than Cl2. NW-EP also achieved much higher removals (∼84.6 % and 89.5 %) of viable Bacillus cereus (G+) and Acinetobacter schindleri (G-) via generating unrecoverable pores on cell wall and reversible/irreversible pores on cell membrane than Cl2 (∼28.6 % and 41.1 %) with insignificant cell damage. The residual VBNC bacteria with cell wall damage and membrane pore resealing exhibited gradual inactivation by osmotic stress, leading to ∼99.8 % cell inactivation after 24 h storage (∼59.4 % for Cl2). Characterizations of cell membrane integrity and cell morphology revealed that osmotic stress promoted cell membrane damage for the gradual inactivation of VBNC cells during storage. The excellent adaptability of NW-EP for controlling VBNC cells in DI, tap and lake waters suggested its promising application potentials for drinking water, such as design of an external device on household taps.

Regulatory Mechanisms of Quorum Sensing System of Bacteria in Response to Chlorine and Ozone Disinfection

Waterborne pathogens invariably present considerable threats to public health. The quorum sensing (QS) system is instrumental in coordinating bacterial growth and metabolisms. However, the responses and regulatory mechanisms of bacteria to various disinfection technologies through quorum sensing are still unclear. This study examines the inactivation effect of chlorination and ozonation on biofilms and planktonic cells of QS signaling-deficient mutants of Pseudomonas aeruginosa. Cell counting and viability assessment revealed that the combined disinfection of chlorine and ozone was the most effective for inactivating planktonic P. aeruginosa within 10 min of exposure. Additionally, microfluidic chip culture demonstrated that the secretion of quinolone signals escalated biofilms' disinfection resistance. Disinfection exposure significantly altered the gene expression of wild-type strains and QS signaling-deficient mutants. Moreover, the QS system triggered multilayered gene expression programs as a responsive protection to disinfectant exposure, including oxidative stress, ribosome synthesis, and the nutrient absorption of bacteria. These insights broaden our understanding of bacterial QS in response to disinfection, promising potential strategies toward efficient disinfection processes.

Evaluation of functional characteristics of Acidithiobacillus thiooxidans microencapsulated in gum arabic by spray-drying as biotechnological tool in the mining industry

The mining and metallurgical industry represents one of the leading causes of environmental pollution. In this context, the optimization of mineral waste management and the efficient extraction of metals of interest becomes an imperative priority for a sustainable future. Microorganisms such as Acidithiobacillus thiooxidans have represented a sustainable and economical alternative in recent years due to their capacity for environmental remediation in bioleaching processes because of their sulfur-oxidizing capacity and sulfuric acid generation. However, its use has been limited due to the reluctance of mine operators because of the constant reproduction of the bacterial culture in suitable media and the care that this entails. In this work, the central objective was to evaluate the functional characteristics of A. thiooxidans, microencapsulated and stored at room temperature for three years in vacuum bags, using a spray drying process with gum arabic as a wall vector. Growth kinetics showed a survival of 80 ± 0.52% after this long period of storage. Also, a qualitative fluorescence technique with a 5-cyano-2-3 ditolyl tetrazolium (CTC) marker was used to determine the respiratory activity of the microorganisms as soon as it was resuspended. On the other hand, the consumption of resuspended sulfur was evaluated to corroborate the correct metabolic functioning of the bacteria, with results of up to 50% sulfur reduction in 16 days and sulfate generation of 513.85 ± 0.4387 ppm and 524.15 ± 0.567 ppm for microencapsulated and non-microencapsulated cultures, respectively. These results demonstrate the success after three years of the microencapsulation process and give guidelines for its possible application in the mining-metallurgical industry.

Exploring the Antimicrobial Efficacy of Low-Cost Commercial Disinfectants Utilized in the Agro-Food Industry Wash Tanks: Towards Enhanced Hygiene Practices

The increase in vegetable consumption has underlined the importance of minimizing the risks associated with microbiological contamination of fresh produce. The critical stage of the vegetable washing process has proven to be a key point for cross-contamination and the persistence of pathogens. In this context, the agri-food industry has widely adopted the use of disinfectants to reduce the bacterial load in the wash water. Therefore, we conducted laboratory-scale experiments in order to demonstrate the antimicrobial activity of disinfectants used in the wash tank of agro-food industries. Different wash water matrices of shredded lettuce, shredded cabbage, diced onion, and baby spinach were treated with sodium hypochlorite (NaClO), chlorine dioxide (ClO2), and per-oxyacetic acid (PAA) at recommended concentrations. To simulate the presence of pathogenic bacteria, a cocktail of E. coli O157:H7 was inoculated into the process water samples (PWW) to determine whether concentrations of disinfectants inhibit the pathogen or bring it to a viable non-culturable state (VBNC). Hereby, we used quantitative qPCR combined with different photo-reactive dyes such as ethidium monoazide (EMA) and propidium monoazide (PMA). The results indicated that concentrations superior to 20 ppm NaClO inhibit the pathogen E. coli O157:H7 artificially inoculated in the process water. Concentrations between 10-20 ppm ClO2 fail to induce the pathogen to the VBNC state. At concentrations of 80 ppm PAA, levels of culturable bacteria and VBNC of E. coli O157:H7 were detected in all PWWs regardless of the matrix. Subsequently, this indicates that the recommended concentrations of ClO2 and PAA for use in the fresh produce industry wash tank do not inhibit the levels of E. coli O157:H7 present in the wash water.

Chlorite and bromate alter the conjugative transfer of antibiotic resistance genes: Co-regulation of oxidative stress and energy supply

The widespread use of disinfectants during the global response to the 2019 coronavirus pandemic has increased the co-occurrence of disinfection byproducts (DBPs) and antibiotic resistance genes (ARGs). Although DBPs pose major threats to public health globally, there is limited knowledge regarding their biological effects on ARGs. This study aimed to investigate the effects of two inorganic DBPs (chlorite and bromate) on the conjugative transfer of RP4 plasmid among Escherichia coli strains at environmentally relevant concentrations. Interestingly, the frequency of conjugative transfer was initially inhibited when the exposure time to chlorite or bromate was less than 24 h. However, this inhibition transformed into promotion when the exposure time was extended to 36 h. Short exposures to chlorite or bromate were shown to impede the electron transport chain, resulting in an ATP shortage and subsequently inhibiting conjugative transfer. Consequently, this stimulates the overproduction of reactive oxygen species (ROS) and activation of the SOS response. Upon prolonged exposure, the resurgent energy supply promoted conjugative transfer. These findings offer novel and valuable insights into the effects of environmentally relevant concentrations of inorganic DBPs on the conjugative transfer of ARGs, thereby providing a theoretical basis for the management of DBPs.

The secondary outbreak risk and mechanisms of Microcystis aeruginosa after H2O2 treatment

The secondary outbreak of cyanobacteria after algicide treatment has been a serious problem to water ecosystems. Hydrogen peroxide (H2O2) is an algaecide widely used in practice, but similar re-bloom problems are inevitably encountered. Our work found that Microcystis aeruginosa (M. aeruginosa) temporarily hibernates after H2O2 treatment, but there is still a risk of secondary outbreaks. Interestingly, the dormant period was as long as 20 and 28 days in 5 mg L-1 and 20 mg L-1 H2O2 treatment groups, respectively, but the photosynthetic activity was both restored much earlier (within 14 days). Subsequently, a quantitative imaging flow cytometry-based method was constructed and confirmed that the re-bloom had undergone two stages including first recovery and then re-division. The expression of ftsZ and fabZ genes showed that M. aeruginosa had active transcription processes related to cell division protein and fatty acid synthesis during the dormancy stat. Furthermore, metabolomics suggested that the recovery of M. aeruginosa was mainly by activating folate and salicylic acid synthesis pathways, which promoted environmental stress resistance, DNA synthesis, and cell membrane repair. This study reported the comprehensive mechanisms of secondary outbreak of M. aeruginosa after H2O2 treatment. The findings suggest that optimizing the dosage and frequency of H2O2, as well as exploring the potential use of salicylic acid and folic acid inhibitors, could be promising directions for future algal control strategies.

Revealing the mechanism of citral induced entry of Vibrio vulnificus into viable but not culturable (VBNC) state based on transcriptomics

Citral has attracted much attention as a safe and effective plant-derived bacteriostatic agent. However, the ability of citral to induce the formation of VBNC state in Vibrio vulnificus has not been evaluated. In the present study, V. vulnificus was shown to be induced to form the VBNC state at 4.5 h and 3 h of citral treatment at 4MIC and 6MIC. Moreover, the citral-induced VBNC state of V. vulnificus maintained some respiratory chain activity and was able to recover well in both APW media, APW media supplemented with 5 % (v/v) Tween 80 and 2 mg/mL sodium pyruvate. Field emission and transmission electron microscopy showed that the external structure of the citral-induced VBNC V. vulnificus cells was shortened to short rods, with folded cell membrane, rough cell surface, and dense cytoplasm and loose nuclear material in the internal cell structure. In addition, the possible molecular mechanisms of citral-induced formation and recovery of V. vulnificus in the VBNC state were explored by transcriptomics. Transcriptome analyses revealed that 1118 genes were significantly altered upon entry into the VBNC state, and 1052 genes were changed after resuscitation. Most of the physiological activities related to energy production were inhibited in the citral-induced VBNC state of V. vulnificus; however, the bacteria retained its pathogenicity. The citral-induced resuscitation of V. vulnificus in the VBNC state selectively restored the activity of some genes related to bacterial growth and reproduction. Meanwhile, the expression levels of other genes may have been influenced by citral-induced resuscitation after the formation of the VBNC state. In conclusion, this study evaluated and analyzed the ability and possible mechanism of citral on the formation of VBNC state and the recovery of VBNC state of V. vulnificus, and made a comprehensive assessment for the safety of citral application in food production.

Gamma-ray irradiation as an effective method for mitigating antibiotic resistant bacteria and antibiotic resistance genes in aquatic environments

The prevalence of antibiotic resistance genes (ARGs) in municipal wastewater treatment plants (MWTPs) has emerged as a significant environmental concern. Despite advanced treatment processes, high levels of ARGs persist in the secondary effluent from MWTPs, posing ongoing environmental risks. This study explores the potential of gamma-ray irradiation as a novel approach for sterilizing antibiotic-resistant bacteria (ARB) and reducing ARGs in MWTP secondary effluent. Our findings reveal that gamma-ray irradiation at an absorbed dose of 1.6 kGy effectively deactivates all culturable bacteria, with no subsequent revival observed after exposure to 6.4 kGy and a 96-h incubation in darkness at room temperature. The removal efficiencies for a range of ARGs, including tetO, tetA, blaTEM-1, sulI, sulII, and tetW, were up to 90.5% with a 25.6 kGy absorbed dose. No resurgence of ARGs was detected after irradiation. Additionally, this study demonstrates a considerable reduction in the abundances of extracellular ARGs, with the transformation efficiencies of extracellular tetracycline and sulfadiazine resistance genes decreasing by 56.3-81.8% after 25.6 kGy irradiation. These results highlight the effectiveness of gamma-ray irradiation as an advanced and promising method for ARB sterilization and ARG reduction in the secondary effluent of MWTPs, offering a potential pathway to mitigate environmental risks associated with antibiotic resistance.

Challenges and mitigation strategies associated with Burkholderia cepacia complex contamination in pharmaceutical manufacturing

Burkholderia cepacia complex (BCC) is a Gram-negative, non-spore-forming bacterium with more than 20 opportunistic pathogenic species, most commonly found in soil and water. Due to their rapid mutation rates, these organisms are adaptable and possess high genomic plasticity. BCC can cause life-threatening infections in immunocompromised individuals, such as those with cystic fibrosis, chronic granulomatous disease, and neonates. BCC contamination is a significant concern in pharmaceutical manufacturing, frequently causing non-sterile product recalls. BCC has been found in purified water, cosmetics, household items, and even ultrasound gel used in veterinary practices. Pharmaceuticals, personal care products, and cleaning solutions have been implicated in numerous outbreaks worldwide, highlighting the risks associated with intrinsic manufacturing site contamination. Regulatory compliance, product safety, and human health protection depend on testing for BCC in pharmaceutical manufacturing. Identification challenges exist, with BCC often misidentified as other bacteria like non-lactose fermenting Escherichia coli or Pseudomonas spp., particularly in developing countries where reporting BCC in pharmaceuticals remains limited. This review comprehensively aims to address the organisms causing BCC contamination, genetic diversity, identification challenges, regulatory requirements, and mitigation strategies. Recommendations are proposed to aid pharmaceutical chemists in managing BCC-associated risks and implementing prevention strategies within manufacturing processes.

New insights into survival strategies and PCB bioremediation potential of resuscitated strain Achromobacter sp. HR2 under combined stress conditions

The resuscitated strains achieved through the addition of resuscitation promoting factor (Rpf) hold significant promise as bio-inoculants for enhancing the bioremediation of polychlorinated biphenyls (PCBs). Nevertheless, the potential of these resuscitated strains to transition into a viable but non-culturable (VBNC) state, along with the specific stressors that initiate this transformation, remains to be comprehensively elucidated. In this study, a resuscitated strain HR2, obtained through Rpf amendment, was employed to investigate its survival strategies under combined stress involving low temperature (LT), and PCBs, in the absence and presence of heavy metals (HMs). Whole-genome analysis demonstrated that HR2, affiliated with Achromobacter, possessed 107 genes associated with the degradation of polycyclic aromatic compounds. Remarkably, HR2 exhibited effective degradation of Aroclor 1242 and robust resistance to stress induced by LT and PCBs, while maintaining its culturability. However, when exposed to the combined stress of LT, PCBs, and HMs, HR2 entered the VBNC state. This state was characterized by significant decreases in enzyme activities and notable morphological, physiological, and molecular alterations compared to normal cells. These findings uncovered the survival status of resuscitated strains under stressful conditions, thereby offering valuable insights for the development of effective bioremediation strategies.

Unveiling the PCB biodegradation potential and stress survival strategies of resuscitated strain Pseudomonas sp. HR1

The exploration of resuscitated strains, facilitated by the resuscitation promoting factor (Rpf), has substantially expanded the pool of cultivated degraders, enhancing the screening of bio-inoculants for bioremediation applications. However, it remains unknown whether these resuscitated strains can re-enter the viable but non-culturable (VBNC) state and the specific stress conditions that trigger such a transition. In this work, the whole genome, and polychlorinated biphenyl (PCB)-degrading capabilities of a resuscitated strain HR1, were investigated. Notably, the focus of this exploration was on elucidating whether HR1 would undergo a transition into the VBNC state when exposed to low temperature and PCBs, with and without the presence of heavy metals (HMs). The results suggested that the resuscitated strain Pseudomonas sp. HR1 harbored various functional genes related to xenobiotic biodegradation, demonstrating remarkable efficiency in Aroclor 1242 degradation and strong resistance against stress induced by low temperature and PCBs. Nevertheless, when exposed to the combined stress of low temperature, PCBs, and HMs, HR1 underwent a transition into the VBNC state. This transition was characterized by significant decreases in enzyme activities and notable changes in both morphological and physiological traits when compared to normal cells. Gene expression analysis revealed molecular shifts underlying the VBNC state, with down-regulated genes showed differential expression across multiple pathways and functions, including oxidative phosphorylation, glycolysis, tricarboxylic acid cycle, amino acid metabolism, translation and cytoplasm, while up-regulated genes predominantly associated with transcription regulation, membrane function, quorum sensing, and transporter activity. These findings highlighted the great potential of resuscitated strains as bio-inoculants in bioaugmentation and shed light on the survival mechanisms of functional strains under stressful conditions, which should be carefully considered during bioremediation processes.

Combined applications of UV and chlorine on antibiotic resistance control: A critical review

Environmental health problems caused by antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) have become a global concern. ARB and ARGs have been continuously detected in various water environments, which pose a new challenge for water quality safety assurance. Disinfection is a key water treatment process to eliminate pathogenic microorganisms in water, and combined chlorine and UV processes (the UV/Cl2 process, the UV-Cl2 process, and the Cl2-UV process) are considered potential disinfection methods to control antibiotic resistance. This review documented the efficacy and mechanism of combined UV and chlorine processes for the control of antibiotic resistance, as well as the effects of chlorine dose, solution pH, UV wavelength, and water matrix on the effectiveness of the processes. There are knowledge gaps in research on the combined chlorine and UV processes for antibiotic resistance control, in particular the UV-Cl2 process and the Cl2-UV process. In addition, changes in the structure of microbial communities and the distribution of ARGs, which are closely related to the spread of antibiotic resistance in the water, induced by combined processes were also addressed. Whether these changes could lead to the re-transmission of antibiotic resistance and harm human health may need to be further evaluated.

Mitigation of T3SS-mediated virulence in waterborne pathogenic bacteria by multi-electrode cylindrical-DBD plasma-generated nitric oxide water

S. enterica, S. flexneri, and V. parahaemolyticus bacteria are globally recognized to cause severe diarrheal diseases, consisting of Type III Secretion System (T3SS) effectors that help in bacterial infection and virulence in host cells. This study investigates the properties of multi-electrode cylindrical DBD plasma-generated nitric oxide water (MCDBD-PG-NOW) treatment on the survival and virulence of S. enterica, S. flexneri, and V. parahaemolyticus bacteria. The Colony Forming Unit (CFU) assay, live/dead cell staining, lipid peroxidation assay, and bacteria morphological analysis showed substantial growth inhibition of bacteria. Moreover, to confirm the interaction of reactive nitrogen species (RNS) with bacterial membrane biotin switch assay, DAF-FM, and FTIR analysis were carried out, which established the formation of S-nitrosothiols in the cell membrane, intracellular accumulation of RNS, and changes in the cell composition post-PG-NOW treatment. Furthermore, the conventional culture-based method and a quantitative PCR using propidium monoazide showed minimal VBNC induction under similar condition. The efficiency of bacteria to adhere to mammalian colon cells was significantly reduced. In addition, the infection rate was also controlled by disrupting the virulent genes, leading to the collapse of the infection mechanism. This study provides insights into whether RNS generated from PG-NOW might be beneficial for preventing diarrheal infections.

Effects of chlorination on the survival of sewage bacteria in seawater microcosms

Chlorination is a commonly used disinfection method in sewage treatment process. However, resistant bacteria may survive chlorination and enter the receiving aquatic environment upon effluent discharge. There has been limited research on the effects of chlorination on bacterial survival in seawater. To address this knowledge gap, microcosm experiments were conducted to simulate the discharge of chlorinated effluents into coastal seawater. The results revealed that bacterial communities in seawater-based effluents survived better in seawater than those in freshwater-based effluents. High chlorine dosages could significantly reduce the viable bacterial populations and their chance of regrowth in seawater. Additionally, faecal indicator bacteria (FIB) that entered the viable but non-culturable (VBNC) state under chlorination tended to persist in the VBNC state without resuscitation during seawater incubation. Because of the prevalence of VBNC indicator bacteria, qPCR quantification of FIB was more effective than conventional culture-based methods in tracing viable pathogenic chlorine-resistant bacteria, although the correlation strength varied depending on the type of effluent. This study sheds light on how chlorine dosages and the intrinsic properties of effluents affect bacterial survival in seawater and highlights the potential and limitations of using FIB in monitoring the health risks associated with the discharge of chlorinated effluents.

Effects of disinfectant type and dosage on biofilm's activity, viability, microbiome and antibiotic resistome in bench-scale drinking water distribution systems

Drinking water distribution systems (DWDSs) are important for supplying high-quality water to consumers and disinfectant is widely used to control microbial regrowth in DWDSs. However, the disinfectant's influences on microbial community and antibiotic resistome in DWDS biofilms and the underlying mechanisms driving their dynamics remain elusive. The study investigated the effects of chlorine and chloramine disinfection on the microbiome and antibiotic resistome of biofilms in bench-scale DWDSs using metagenomics assembly. Additionally, the biofilm activity and viability were monitored based on adenosine triphosphate (ATP) and flow cytometer (FCM) staining. The results showed that both chlorine and chloramine disinfectants decreased biofilm ATP, although chloramine at a lower dosage (1 mg/L) could increase it. Chloramine caused a greater decrease in living cells than chlorine. Furthermore, the disinfectants significantly lowered the microbial community diversity and altered microbial community structure. Certain bacterial taxa were enriched, such as Mycobacterium, Sphingomonas, Sphingopyxis, Azospira, and Dechloromonas. Pseudomonas aeruginosa exhibited high resistance towards disinfectants. The disinfectants also decreased the complexity of microbial community networks. Some functional taxa (e.g., Nitrospira, Nitrobacter, Nitrosomonas) were identified as keystones in chloramine-treated DWDS microbial ecological networks. Stochasticity drove biofilm microbial community assembly, and disinfectants increased the contributions of stochastic processes. Chlorine had greater promotion effects on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) and ARG hosts than chloramine. The disinfectants also selected pathogens, such as Acinetobacter baumannii and Klebsiella pneumonia, and these pathogens also harbored ARGs and MGEs. Overall, this study provides new insights into the effects of disinfectants on biofilm microbiome and antibiotic resistome, highlighting the importance of monitoring and managing disinfection practices in DWDSs.

Effect of RpoS on the survival, induction, resuscitation, morphology, and gene expression of viable but non-culturable Salmonella Enteritidis in powdered infant formula

Involvement of the transcriptional regulator RpoS in the persistence of viable but non-culturable (VBNC) state has been demonstrated in several species of bacteria. This study investigated the role of the RpoS in the formation and resuscitation of VBNC state in Salmonella enterica serovar Enteritidis CICC 21482 by measuring bacterial survival, morphology, physiological characteristics, and gene expression in wild-type (WT) and rpoS-deletion (ΔrpoS) strains during long-term storage in powdered infant formula (PIF). The ΔrpoS strain was produced by allelic exchange using a suicide plasmid. Bacteria were inoculated into PIF for 635-day storage. Survival, morphology, intracellular reactive oxygen species (ROS) levels and intercellular quorum sensing autoinducer-2 (AI-2) contents were regularly measured. Resuscitation assays were conducted after obtaining VBNC cells. Gene expression was measured using real-time quantitative polymerase chain reaction (qPCR). The results showed that RpoS and low temperature conditions were associated with enhanced culturability and recoverability of Salmonella Enteritidis after desiccation storage in low water activity (aw) PIF. In addition, the synthesis of intracellular ROS and intercellular quorum sensing AI-2 was regulated by RpoS, inducing the formation and resuscitation of VBNC cells. Gene expression of soxS, katG and relA was found strongly associated with RpoS. Due to the lack of RpoS factor, the ΔrpoS strain could not normally synthesize SoxS, catalase and (p)ppGpp, resulting in its early shift to the VBNC state. This study elucidates the role of rpoS in desiccation stress and the formation and resuscitation mechanism of VBNC cells under desiccation stress. It serves as the basis for preventing and controlling the recovery of pathogenic bacteria in VBNC state in low aw foods.

Plasma-generated nitric oxide water: A promising strategy to combat bacterial dormancy (VBNC state) in environmental contaminant Micrococcus luteus

The viable but non-culturable (VBNC) is an inactive state, and certain bacteria can enter under adverse conditions. The VBNC state challenges the environment, food safety, and public health since VBNCs may resuscitate and pose a risk to human health. The aim of this study was to investigate the effect of plasma-generated nitric oxide water (PG-NOW) on airborne contaminant Micrococcus luteus (M. luteus) and examine its potential to induce the VBNC state. The essential conditions for bacteria to enter VBNC state are low metabolic activity and rare or no culturable counts. The results indicated that PG-NOW effectively eliminates M. luteus, and the remaining bacteria are in culturable condition. Moreover, the conventional cultured-based method combined with a propidium iodide monoazide quantitative PCR (PMAxxTM-qPCR) showed no significant VBNC induction and moderate culturable counts. Results from the qPCR revealed that gene levels in PG-NOW treated bacteria related to resuscitation-promoting factors, amino acid biosynthesis, and fatty acid metabolism were notably upregulated. PG-NOW inactivated M. luteus showed negligible VBNC formation and alleviated infection ability in lung cells. This study provides new insights into the potential use of PG-NOW reactive species for the prevention and control of the VBNC state of M. luteus.

Emerging contaminants in the water environment: Disinfection-induced viable but non-culturable waterborne pathogens

Disinfection is essential for the control of waterborne pathogens (WPs), especially during the COVID-19 pandemic. WP can enter the viable but non-culturable (VBNC) state to evade disinfection, seriously threatening water safety. VBNC WPs should be considered as an emerging contaminant to ensure a higher level of safety of the water environment. Here, this study systematically reviewed the water disinfection methods that could induce WPs into the VBNC state, and clarified the risks of different species of VBNC WPs in the relevant water environment. The physicochemical and physiological properties of VBNC cells (e.g., morphology, physiology, and resuscitation potential) were then evaluated to better understand their potential health risks. In addition, the dominant detection methods of VBNC WPs were discussed, and real-time and label-free technologies were recommended for the study of VBNC WPs in the aquatic environment. The possible mechanisms of formation and persistence at the genetic level were highlighted. It concluded that the VBNC state has a deeper level of dormancy than the persistent state, which is associated with the general stress response and stringent response systems, and its persistence is also associated with the active efflux of harmful substances. Finally, the current shortcomings and research perspectives of VBNC bacteria were summarized. This review provides new insights into the characteristics, detection methods, persistence mechanisms, and potential health risks of VBNC WPs induced by water disinfection processes, and also serves as a basis for microbial risk control in the aquatic environment.

Solar/periodate inhibits ARGs transformation by degradation of DNA without damaging cell membrane

Antibiotic-resistant bacterial infections are a growing global threat to public health. Chlorine-based water disinfection and some advanced oxidation processes significantly increase the risk of ARGs release and transmission in the aquatic environment. Therefore, it is critical to develop or optimize disinfection methods to reduce the conversion and transmission of ARGs in natural water. This study investigated whether the solar/periodate (PI) system inhibited the natural transmission of ARGs and its mechanism. The results showed that solar/PI systems could effectively inhibit the propagation of ARGs in two simulated natural transformation systems, up to more than 100 times. By characterizing the cellular process of bacteria treated by the solar/PI system, we found that the solar/PI system could directly cause damage to DNA bases and its dual effect with almost no damage to the bacterial cell membrane, which was the main reason why this technology could inhibit natural transformation processes. Specifically, the inhibition effect of solar/PI on bacteria did not result in enhanced membrane permeability under appropriate PI dosage (<200 μM), which greatly reduced the risk of secondary contamination of eARGs released by traditional disinfection. Our findings could help improve existing disinfection strategies to ensure that antibiotic resistance is not spread in the natural water environment.

Exogenous mobile genetic elements and their associated integrons drive the enrichment of antibiotic-resistant genes in the river of a valley basin city (Lanzhou, China)

River is a unique source of drinking water in valley-type cities, affecting local urban development and human lifestyles. However, the key driving factors for dissemination of antibiotic-resistant genes (ARGs) in valley-type urban environments remain unclear. This study aimed to investigate the distribution of ARGs in the Yellow River and to clarify the driving factors of ARGs in a typical valley basin city (Lanzhou, China). The seven selected ARGs with higher abundances including tetracycline resistance genes (tetM, tetX), macrolide resistance genes (ermB, ermF, ereA), and sulfonamide resistance genes (sul1, sul2) were detected. The results showed that the total absolute abundance of all the selected ARGs varied from 9.97 × 1012 to 1.04 × 1015 copies/L in the water body, with higher abundances in the wet season, relative to the dry season. Among these, sulfonamide resistance genes (sul1, sul2) displayed the highest absolute abundance in the river and soil. The ARGs and mobile genetic elements (MGEs) were significantly correlated with bacterial abundance, dissolved organic carbon (DOC), ammonia nitrogen (NH4+), and total nitrogen (TN) levels in the water environment (Mantel test, P < 0.01). Structural equation modeling revealed the direct input of point-source and nonpoint-source ARGs in this area contributed less to the overall level of the ARGs in the water. Among the multiple drivers, the MGEs derived from wastewater treatment plant and anthropogenic nonpoint area positively and directly affected the ARG profiles in water (P < 0.01), rather than the factors of bacterial abundance and physicochemical properties. According to this study, the exogenous MGEs from anthropogenic activities are the main driver for the enrichment of ARGs in the valley-type urban river environment.

Transcriptomic analysis of Lacticaseibacillus paracasei Zhang in transition to the viable but non-culturable state by RNA sequencing

Background

Some bacteria enter the viable but non-culturable (VBNC) state to survive harsh environmental conditions and external stresses. This alters cell physiology and has implications for the food industry as some bacteria, such as lactobacilli, undergo similar changes during food processing.

Methods

This study aimed to investigate the transcriptomic changes of a probiotic strain, Lacticaseibacillus paracasei Zhang (L. paracasei Zhang), upon transition to the VBNC state using high throughput RNA sequencing (RNA-seq).

Results

Bacteria were inoculated into the de Man, Rogosa, and Sharpe medium and maintained at low temperature and pH to induce cell transition to the VBNC state. Cells were harvested for analysis at five stages of VBNC induction: 0, 3, 30, and 180 days after induction and 210 days when the cells entered the VBNC state. Our results showed that the expression of 2,617, 2,642, 2,577, 2,829, and 2,840 genes was altered at these five different stages. The function of differentially expressed genes (DEGs, compared to healthy cells collected at day 0) and their encoded pathways were analyzed by the Gene Ontology Consortium and the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. A total of 10 DEGs were identified in cells that entered the VBNC state: five continuously upregulated (LCAZH_0621, LCAZH_1986, LCAZH_2038, LCAZH_2040, and LCAZH_2174) and five continuously downregulated (LCAZH_0024, LCAZH_0210, LCAZH_0339, LCAZH_0621, and LCAZH_0754).

Conclusions

This study proposes a molecular model of the VBNC mechanism in L. paracasei Zhang, highlighting that changes in cell metabolism improve substrate utilization efficiency, thereby enhancing bacterial survival under adverse conditions. These data may be useful for improving the survival of probiotics in industrial food processing.

Inactivation of Bacteria in Water by Ferrate(VI): Efficiency and Mechanisms

Ferrate (Fe(VI)) is an emerging green disinfectant and has received increasing attention nowadays. This study conducted systematic analyses of Fe(VI) disinfection on six typical bacteria in different water matrices. The results showed that Fe(VI) was more effective in inactivating Gram-negative (G-) bacteria than Gram-positive (G+) bacteria, and the disinfection performance of Fe(VI) was better in a phosphate buffer than that in a borate buffer and secondary effluent. The inactivation rate constants of G- bacteria were significantly higher than those of G+ bacteria. The cell membrane damage of G- bacteria was also more severe than that of G+ bacteria after Fe(VI) treatment. The cell wall structure, especially cell wall thickness, might account for the difference of the inactivation efficiency between G- bacteria and G+ bacteria. Moreover, it is revealed that Fe(VI) primarily reacted with proteins rather than other biological molecules (i.e., phospholipids, peptidoglycan, and lipopolysaccharide). This was further evidenced by the reduction of bacterial autofluorescence due to the destruction of bacterial proteins during Fe(VI) inactivation. Overall, this study advances the understanding of Fe(VI) disinfection mechanisms and provides valuable information for the Fe(VI) application in water disinfection.

Effect of CeO2 Nanoparticles on the Spread of Antibiotic Resistance in a Reclaimed Water-Soil-Radish System - Shenzhen City, Guangdong Province, China, April 2023

Introduction

The use of reclaimed water (RW) for irrigation in agricultural practices raises concerns regarding the dissemination of antibiotic resistance genes (ARGs) from soils to edible crops. The effectiveness of nanoparticles (NPs) in reducing antibiotic resistance in vegetables irrigated with RW remains largely unexplored.

Methods

To investigate the effects, we conducted pot experiments in which radishes were planted in soil amended with CeO2 NPs using various application techniques. The abundance of ARGs was characterized using high-throughput quantitative PCR (HT-qPCR). Concurrently, we utilized 16S ribosomal RNA (rRNA) gene sequencing to evaluate the microbial community structure of both the rhizosphere soil and the endophytic compartment within the radishes. Employing bioinformatics analysis, we probed the potential mechanisms by which NPs influence the resistome within the reclaimed water-soil-radish system.

Results

Following the application of CeO2 NPs, there was a noticeable reduction in both the number and concentration of ARG genotypes in the rhizosphere soil, as well as within the radish. Concurrently, CeO2 NPs appeared to mitigate the propagation of ARGs within the reclaimed water-soil-radish system. The ability of CeO2 NPs to modulate the resistome is linked to alterations in microbial community structure. Soil treatment with NPs emerged as the most effective strategy for curbing the spread of ARGs.

Discussion

This finding provides a theoretical foundation for the development of nano-agricultural technologies aimed at controlling the proliferation of ARGs.

The temperature-dependent kinetics and bacteria regrowth by performic acid and sodium hypochlorite disinfection

Sodium hypochlorite (NaOCl) has been widely used as a disinfectant in water and wastewater treatment, because of its high efficiency and low cost, whereas the bio-toxicity of its disinfection byproducts (DBPs) raised great concern. Performic acid (PFA) produces less DBPs and shows strong oxidation abilities. In this study, the effect of temperature on NaOCl and PFA disinfection as well as bacteria regrowth were evaluated. First, the inactivation of Escherichia coli, Staphylococcus aureus, and Bacillus subtilis by NaOCl and PFA at 4 and 20 °C, detected by cell cultured-based plate counting were fitted to kinetic models, and the predicted CTs were calculated. The results showed that NaOCl was more effective than PFA for E. coli and S. aureus inactivation, and the temperature was positively correlated to disinfection. Second, bacteria regrowth was evaluated at different temperatures (4 and 20 °C) of disinfection and storage. The results showed that the bacteria inactivated by NaOCl regrew prominently, especially for those inactivated at 4 and stored at 4 °C, probably through the mechanism of reactivation of viable but non-culturable (VBNC) bacteria. PFA was superior in suppressing bacteria regrowth, and it may be used as an alternate disinfectant in water treatment in cold environment.

Treatment of clinical laboratory sewage using a decentralized treatment unit and risk reduction for its reuse in irrigation using hybrid disinfection

The disinfection efficacy of standalone chlorine, UV and their combined approach (hybrid) was investigated for the coliform removal in BioKube 1 and 2 treated effluents collected from different environmental settings of clinical and domestic wastes. Chlorine and UV disinfection were applied to BioKube treated wastewater with doses from 0 to 4 mg L-1 and 0-166 mJ cm-2 respectively. Combined disinfection strategies were designed to reduce the dose of chlorine and UV and to exploit the synergistic effect of them. The culturable coliforms were enumerated in treated wastewater sample (control), immediately after (reduction), and 24 h post disinfections (regrowth) using culture media plating and colilert-18 media. Both the BioKube systems (1 and 2) were effective in achieving the strict norms of physicochemical parameters, but not following the coliform counts of treated effluent for reuse in irrigation. A hybrid strategy of chlorine followed by UV was found to be the most effective among various standalone and combination approaches for the removal of coliforms (>4 log ER or <1000 CFU/100 mL) from both the treated effluents. However, coliform present in treated effluent of BioKube 1 were resisting (regrowth) against all kind of applied disinfectants except chlorine followed by UV dose at or more than 0.5 mg L-1 + 41 mJ cm-2. Limited reports are available on hybrid disinfection approaches with decentralized packaged sewage treatment units and this study would help to adopt as an effective tertiary treatment strategy for reuse of treated sewage for irrigation while ensuring public health safety.

Self-repair and resuscitation of viable injured bacteria in chlorinated drinking water: Achromobacter as an example

Chlorine disinfection for the treatment of drinking water can cause injury to the membrane and DNA of bacterial cells and may induce the surviving injured bacteria into a viable but non-culturable (VBNC) state. It is difficult to monitor viable injured bacteria by heterotrophic plate counting (HPC), and their presence is also easily miscalculated in flow cytometry intact cell counting (FCM-ICC). Viable injured bacteria have a potential risk of resuscitation in drinking water distribution systems (DWDSs) and pose a threat to public health when drinking from faucets. In this study, bacteria with injured membranes were isolated from chlorinated drinking water by FCM cell sorting. The culture rate of injured bacteria varied from 0.08% to 2.6% on agar plates and 0.39% to 6.5% in 96-well plates. As the dominant genus among the five identified genera, as well as an opportunistic pathogen with multiple antibiotic resistance, Achromobacter was selected and further studied. After treatment with chlorine at a concentration of 1.2 mg/L, Achromobacter entered into the intermediate injured state on the FCM plot, and the injury on the bacterial surface was observed by electron microscopy. However, the CTC respiratory activity assay showed that 75.0% of the bacteria were still physiologically active, and they entered into a VBNC state. The injured VBNC Achromobacter in sterile drinking water were resuscitated after approximately 25 h. The cellular repair behavior of injured bacteria was studied by Fourier transform infrared attenuated total reflectance (FTIR-ATR) and comet assays. It was found that DNA injury rather than membrane injury was repaired first. The expression of Ku and ligD increased significantly during the DNA repair period, indicating that non-homologous end-joining (NHEJ) played an important role in repairing DNA double-strand breaks. This study deepened the understanding of the effect of chlorine disinfection on bacterial viability in drinking water and will provide support for the improvement of the chlorine disinfection process for the treatment of drinking water.

Hidden risks: Simulated leakage of domestic sewage to secondary water supply systems poses serious microbiological risks

There are continuous reports about the pollution of the secondary water supply systems (SWSSs), among which domestic sewage leakage is the most serious. In this study, a pilot experiment lasting 70 days was conducted to explore the changes in physicochemical water quality and the microbial profiles in SWSSs polluted by different doses of domestic sewage through qPCR and high-throughput sequencing methods. The results showed that when domestic sewage entered the simulated water storage tank, a large amount of organic matter brought by domestic sewage quickly consumed chlorine disinfectants. High pollution levels (pollution index ≥ 1/1000) were accompanied by significant increases in turbidity and ammonia nitrogen concentration (p < 0.05) and by abnormal changes in sensory properties. Although different microbial community structures were found only at high pollution levels, qPCR results showed that the abundance of the bacterial 16S rRNA gene and some pathogenic gene markers in the polluted tank increased with the pollution level, and the specific gene marker of pathogens could be detected even at imperceptible pollution levels. In particular, the high detection frequency and abundance of Escherichia coli and Enterococcus faecails in polluted tank water samples demonstrated that they can be used for early warning. Moreover, it seems that the microorganisms that came with the domestic sewage lost their cultivability soon after entering SWSSs but could recover their activities during stagnation. In addition, the biofilm biomass in the polluted tank with high pollution levels increased faster at the initial stage, while after a longer contact time, it tended to remain at the same level as the control tank. This study emphasized the high microbial risk introduced by sewage water leakage even at imperceptible levels and could provide scientific suggestions for early warning and prevention of pollution to SWSSs.

Convergence of flow cytometry and bacteriology. Current and future applications: a focus on food and clinical microbiology

Since its development in the 1960s, flow cytometry (FCM) was quickly revealed a powerful tool to analyse cell populations in medical studies, yet, for many years, was almost exclusively used to analyse eukaryotic cells. Instrument and methodological limitations to distinguish genuine bacterial signals from the background, among other limitations, have hampered FCM applications in bacteriology. In recent years, thanks to the continuous development of FCM instruments and methods with a higher discriminatory capacity to detect low-size particles, FCM has emerged as an appealing technique to advance the study of microbes, with important applications in research, clinical and industrial settings. The capacity to rapidly enumerate and classify individual bacterial cells based on viability facilitates the monitoring of bacterial presence in foodstuffs or clinical samples, reducing the time needed to detect contamination or infectious processes. Besides, FCM has stood out as a valuable tool to advance the study of complex microbial communities, or microbiomes, that are very relevant in the context of human health, as well as to understand the interaction of bacterial and host cells. This review highlights current developments in, and future applications of, FCM in bacteriology, with a focus on those related to food and clinical microbiology.

Metabolome shifts triggered by chlorine sanitisation induce Escherichia coli on fresh produce into the viable but nonculturable state

Facing the increasing occurrence of "big six" Escherichia coli outbreaks linked to fresh produce, chlorine-based sanitisers are widely used for fresh produce decontamination in recent years. However, latest finding that chlorine may induce E. coli cells into a viable not nonculturable (VBNC) state is bringing a new challenge to the fresh produce industry. VBNC cells are undetectable by the plate count test, and yet they retain pathogenicity and are more antibiotic-resistant than culturable cells. As a result, their eradication is critical to ensure the safety of fresh produce. Understanding VBNC cells at the metabolic level may provide a breakthrough for their eradication. Therefore, this study was carried out to collect the VBNC pathogenic E. coli (O26:H11, O121:H19, and O157:H7) cells from chlorine-treated pea sprouts and characterise them using NMR-based metabolomics. From the globally increased metabolite contents detected in the VBNC E. coli cells as compared to the culturable cells, mechanisms underlying E. coli's VBNC induction were elucidated. These include rendering the energy generation scheme to become more compatible with the lowered energy needs, disaggregating protein aggregates to release amino acids for osmoprotection and later resuscitation, as well as increasing cAMP content to downregulate RpoS. These identified metabolic characteristics can inspire future development of targeted measures for VBNC E. coli cell inhibition. Our methods can also be applied to other pathogens to help lower the risk of overall foodborne diseases.

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.

Influence of CoOx surface passivation and Sn/Zr-co-doping on the photocatalytic activity of Fe2O3 nanorod photocatalysts for bacterial inactivation and photo-Fenton degradation

Hydrothermal and wet impregnation methods are presented in this study for synthesizing CoO_x(1 wt%)/Sn-Zr codoped-Fe₂O₃ nanorod photocatalysts for the degradation of organic pollutants and deactivation of bacteria. A hydrothermal route was used to synthesize self-assembled rod-like hierarchical structures of Sn(0-6%) doped Zr-Fe₂O₃ NRs. Additionally, a wet impregnation method was used to load CoO_x onto the surface of photocatalysts (Sn(0-6%)-doped Zr-Fe₂O₃ NRs). A series of 1 wt% CoO_x modified Sn(0-6%)-doped Zr-Fe₂O₃ NRs were synthesized, characterized, and utilized for the photocatalytic decomposition of organic contaminants, along with the killing of E. coli and S. aureus. In comparison with 0, 2, and 6% Sn co-doped Zr-Fe₂O₃ NRs, the CoO_x(1 wt%)/4%Sn/Zr-Fe₂O₃ NRs photocatalyst exhibited an E. coli and S. aureus inactivation efficiencies (90 and 98%). A bio-TEM study of treated and untreated bacterial cells revealed that the CoO_x(1 wt%)/4%Sn/Zr-Fe₂O₃ NRs photocatalyst led to considerable changes in the bacterial cell membranes' morphology. The optimal CoO_x(1 wt%)/Sn(4%) co-doped Zr-Fe₂O₃ NRs photocatalyst achieved degradation efficiencies of 98.5% and 94.6% for BPA and orange II dye. As a result, this work will provide a facile and effective method for developing visible light-active photocatalysts for bacterial inactivation and organic pollutants degradation.

Susceptibility of Campylobacter jejuni to Stressors in Agrifood Systems and Induction of a Viable-but-Nonculturable State

Many bacteria can become viable but nonculturable (VBNC) in response to stressors commonly identified in agrifood systems. Campylobacter is able to enter the VBNC state to evade unfavorable environmental conditions, but how food processing can induce Campylobacter jejuni to enter this state and the potential role of foods in inducing the VBNC state in C. jejuni remains largely unknown. In this study, the culturability and viability of C. jejuni cells were investigated under chlorine treatment (25 ppm), aerobic stress (atmospheric condition), and low-temperature (4°C) conditions that mimicked food processing. In addition, the behaviors of C. jejuni cells in ultrahigh-temperature (UHT) and pasteurized milk were also monitored during refrigerated storage. The numbers of viable and culturable C. jejuni cells in both the pure bacterial culture and food matrices were separately determined by propidium monoazide (PMA)-quantitative PCR (qPCR) and plating assay. The C. jejuni cells lost their culturability but partially retained their viability (1% to 10%) once mixed with chlorine. In comparison, ~10% of C. jejuni cells were induced to enter the VBNC state after 24 h and 20 days under aerobic and low-temperature conditions, respectively. The viability of the C. jejuni cells remained stable during the induction process in UHT (>10%) and pasteurized (>10%) milk. The number of culturable C. jejuni cells decreased quickly in pasteurized milk, but culturable cells could still be detected in the end (day 21). In contrast, the number of culturable C. jejuni cells slowly decreased, and they became undetectable after >42 days in UHT milk. The C. jejuni cells responded differently to various stress conditions and survived in high numbers in the VBNC state in agrifood systems. IMPORTANCE The VBNC state of pathogens can pose risks to food safety and public health because the pathogens cannot be detected using conventional microbiological culture-based methods but can resuscitate under favorable conditions to develop virulence. As a leading cause of human gastroenteritis worldwide, C. jejuni can enter the VBNC state to survive in the environment and food-processing chain with high prevalence. In this study, the effect of food-processing conditions and food products on the development of VBNC state in C. jejuni was investigated, providing a better understanding of the interaction between C. jejuni and the agroecosystem. The knowledge elicited from this study can aid in developing novel intervention strategies to reduce the food safety risks associated with this microbe.

Dark repair of sunlight-inactivated tetracycline-resistant bacteria: Mechanisms and important role of bacteria in viable but non-culturable state

The spread of antibiotic resistant bacteria (ARB) in the environment poses a potential threat to human health, and the reactivation of inactivated ARB accelerated the spread of ARB. However, little is known about the reactivation of sunlight-inactivated ARB in natural waters. In this study, the reactivation of sunlight-inactivated ARB in dark conditions was investigated with tetracycline-resistant E. coli (Tc-AR E. coli) as a representative. Results showed that sunlight-inactivated Tc-AR E. coli underwent dark repair to regain tetracycline resistance with dark repair ratios increasing from (0.124 ± 0.012)‱ within 24 h dark treatment to (0.891 ± 0.033)‱ within 48 h. The presence of Suwannee River fulvic acid (SRFA) promoted the reactivation of sunlight-inactivated Tc-AR E. coli and tetracycline inhibited their reactivation. The reactivation of sunlight-inactivated Tc-AR E. coli is mainly attributed to the repair of the tetracycline-specific efflux pump in the cell membrane. Tc-AR E. coli in a viable but non-culturable (VBNC) state was observed and dominated the reactivation as the inactivated ARB remain present in the dark for more than 20 h. These results explained the reason for distribution difference of Tc-ARB at different depths in natural waters, which are of great significance for understanding the environmental behavior of ARB.

Glyoxylate cycle maintains the metabolic homeostasis of Pseudomonas aeruginosa in viable but nonculturable state induced by chlorine stress

Bacteria enter a viable but non-culturable (VBNC) state with low metabolic activity to cope with environmental stress (e.g., chlorine disinfection). Elucidating the mechanism and key pathway of VBNC bacteria maintaining low metabolic competence is of great significance to realize their effective control and reduce their environmental and health risks. This study discovered that the glyoxylate cycle is a key metabolic pathway for VBNC bacteria, but not for culturable bacteria. And blocking the glyoxylate cycle pathway inhibited the reactivation and led to the death of VBNC bacteria. The main mechanisms involved the breakdown of material and energy metabolism and the antioxidant system. Gas chromatography-tandem mass spectrometry analysis showed that blocking the glyoxylate cycle led to a disruption of carbohydrate metabolism and fatty acid catabolism in VBNC bacteria. As a result, the energy metabolism system of VBNC bacteria collapsed and the abundance of energy metabolites (ATP, NAD⁺ and NADP⁺) decreased significantly. Moreover, the decrease in the level of quorum sensing signaling molecules (quinolinone and N-Butanoyl-D-homoserine lactone) inhibited the synthesis of extracellular polymeric substances (EPSs) and biofilm formation. And the downregulation of glycerophospholipid metabolic competence increased the permeability of cell membranes, leading to the entry of large amounts of hypochlorous acid (HClO) into the bacteria. In addition, the down-regulation of nucleotide metabolism, glutathione metabolism, and the reduction of antioxidant enzyme content resulted in the inability to scavenge reactive oxygen species (ROS) generated by chlorine stress. The large production of ROS and the reduction of antioxidants together led to the breakdown of the antioxidant system of VBNC bacteria. In short, the glyoxylate cycle is the key metabolism pathway of VBNC bacteria for stress resistance and maintaining cellular metabolic balance, and targeting the glyoxylate cycle represents an attractive strategy for developing new and efficient disinfection methods for the control of VBNC bacteria.

Analysis of rainwater storage and use recommendations: From the perspective of DBPs generation and their risks

As a vital freshwater resource, rainwater is usually stored in water cellars in arid regions to solve the daily drinking water problems of the population. However, the status of disinfection by-products (DBPs) generation in cellar water under intermittent disinfection conditions is unclear. Therefore, we investigated the formation and distribution characteristics of DBPs in cellar water under intermittent disinfection conditions for the first time. The results demonstrated that six categories of DBPs were selected for detection after chlorination, including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs), haloacetonitriles (HANs), halonitromethanes (HNMs), and nitrosamines (NAs), among which HAAs, HKs, and HANs were the major DBPs. Only bromoacetic acid (MBAA), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA) showed an increasing trend of accumulation as the number of disinfections increased. Meanwhile, the precursor composition was gradually transformed from humic substances to amino acids, and both organic substances were the main precursors of HAAs. The health risk assessment showed that the main carcinogenic and non-carcinogenic risks of cellar water were contributed by NAs and HAAs, respectively, and children are more susceptible to the risks than adults. The best time to drink cellar water is after approximately 12 days of storage, when the total carcinogenic risk is the minimum.

Evaluation of the disinfection effect and mechanism of SO4•- and HO• UV/persulfate salts

Although ultraviolet (UV) and persulfate (PS) have been widely used in water disinfection process, their incompleteness of disinfection, such as inducing the production of viable but non-culturable cells (VBNC), has attracted extensive attention. In this study, the disinfection effect of combined UV and PS was evaluated, and the roles of SO₄^•- and HO^• radicals in UV/PS disinfection were also analyzed. UV/PS more effectively inactivated cells and reduced the number of culturable cells. Also, the test of bacterial dark activation suggested that UV/PS disinfection inhibited the recovery of VBNC bacteria. The mechanisms of UV/PS disinfection were the increase of membrane permeability and oxidative stress, where SO₄^•- radicals played more role than HO^• radicals. Furthermore, UV/PS disinfection more significantly perturbed the metabolism of Pseudomonas aeruginosa (p < 0.05), mainly involving glyoxylate and dicarboxylic acid metabolism, aminoacyl-tRNA biosynthesis, Alanine, aspartate and glutamate metabolism, and citric acid cycle (TCA cycle). In short, UV/PS disinfection can not only significantly reduce the number of culturable bacteria (kill bacteria) but also inhibits the recovery of VBNC bacteria.

Extended lag phase indicates the dormancy of biphenyl degrading Rhodococcus biphenylivorans TG9 under heat stress

Microbial remediation is a green and sustainable technology, but harsh environmental conditions could lead to microbial dormancy, such as entering a viable but non-culturable (VBNC) state. However, the evidence of VBNC is controversial and limited. In this study, heat stress (60 °C), one of the leading challenges for mesophilic degrading bacteria, was mimicked to investigate the physiological response of Rhodococcus biphenylivorans TG9. After 2 h of heat stress, the culturable TG9 cell count decreased from 10⁸ cells/mL to undetectable while the viable cell count was still 10⁵ cells/mL. The biphenyl degradation efficiency of stressed TG9 dropped by 50% compared to that of cells at logarithmic phase. During heat stress, the respiratory activity of TG9 declined dramatically while the intracellular ATP level initially increased and then decreased. Notably, the corresponding indicators recovered when restored to 30 °C. These characteristics were in consistent with bacteria entering into VBNC state. Furthermore, fluorescence activated cell sorting together with single cell as seed culture detection verified the unculturability and viability of VBNC state of TG9 cells. Also, we found that single cells in VBNC state could resuscitate and regrowth with significantly extended lag phase (LP). Our results highlight the potential of TG9 for microbial remediation and hint LP duration as an indicator for survival state of bacteria.

A new acridine-based photosensitizer with ultra-low light requirement efficiently inactivates carbapenem-resistant Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus and degrades their antibiotic resistance genes

The spread of antibiotic resistant pathogens and antibiotic resistance genes (ARGs) in the environment poses a serious threat to public health. However, existing methods are difficult to effectively remove antibiotic resistant pathogens and ARGs from the environment. In this study, we synthesized a new acridine-based photosensitizer, 2,7-dibromo-9-mesityl-10-methylacridinium perchlorate (YM-3), by the heavy atom effect, which could photodynamically inactivate antibiotic resistant pathogens and reduce ARGs by generating singlet oxygen (¹O₂) in an aqueous environment. The ¹O₂ yield of YM-3 was 4.9 times that of its modified precursor. YM-3 could reduce the culturable number and even the viable counts of methicillin-resistant Staphylococcus aureus and carbapenem-resistant Acinetobacter baumannii to 0 (inactivation rate > 99.99999%) after 2 and 8 h of low-intensity blue light (15 W/m²) irradiation, respectively. After 20 h of light exposure, the copy numbers of ARGs in both bacteria were reduced by 5.80 and 4.48 log, respectively, which might indicate that ARGs had been degraded. In addition, YM-3 still had an efficient bactericidal effect after five inactivation cycle. These characteristics of ultra-low light intensity requirement and efficient bactericidal ability make YM-3 have good application prospects for disinfection in indoor and sunlight environment.

Uncovering novel disinfection mechanisms of solar light/periodate system: The dominance of singlet oxygen and metabolomic insights

Disinfection plays an essential role in waterborne pathogen control and disease prevention, especially during the COVID-19 pandemic. Catalyst-free solar light/periodate (PI) system has recently presented great potential in water disinfection, whereas the in-depth chemical and microbiological mechanisms for efficient bacterial inactivation remain unclear. Our work delineated firstly the critical role of singlet oxygen, instead of reported hydroxyl radicals and superoxide radicals, in dominating bacterial inactivation by the PI/simulated sunlight (SSL) system. Multi-evidence demonstrated the prominent disinfection performance of this system for Staphylococcus aureus in terms of culturability (&gt; 6 logs CFU), cellular integrity, and metabolic activity. Particularly, the excellent intracellular DNA removal (&gt; 95%) indicated that PI/SSL system may function as a selective disinfection strategy to diminish bacterial culturability without damaging the cell membrane. The PI/SSL system could also effectively inhibit bacterial regrowth for &gt; 5 days and horizontal gene transfer between E. coli genera. Nontargeted metabolomic analysis suggested that PI/SSL system inactivated bacteria by triggering the accumulation of intracellular reactive oxygen species and the depletion of reduced glutathione. Additionally, the PI/SSL system could accomplish simultaneous micropollutant removal and bacterial inactivation, suggesting its versatility in water decontamination. Overall, this study deciphers more comprehensive antibacterial mechanisms of this environmentally friendly disinfection system, facilitating the technical development and application of the selective disinfection strategy in environmental pathogen control.

Maintaining Antibacterial Activity against Biofouling Using a Quaternary Ammonium Membrane Coupling with Electrorepulsion

Antibacterial modification is a chemical-free method to mitigate biofouling, but surface accumulation of bacteria shields antibacterial groups and presents a significant challenge in persistently preventing membrane biofouling. Herein, a great synergistic effect of electrorepulsion and quaternary ammonium (QA) inactivation on maintaining antibacterial activity against biofouling has been investigated using an electrically conductive QA membrane (eQAM), which was fabricated by polymerization of pyrrole with QA compounds. The electrokinetic force between negatively charged Escherichia coli and cathodic eQAM prevented E. coli cells from reaching the membrane surface. More importantly, cathodic eQAM accelerated the detachment of cells from the eQAM surface, particularly for dead cells whose adhesion capacity was impaired by inactivation. The number of dead cells on the eQAM surface was declined by 81.2% while the number of live cells only decreased by 49.9%. Characterization of bacteria accumulation onto the membrane surface using an electrochemical quartz crystal microbalance revealed that the electrorepulsion accounted for the cell detachment rather than inactivation. In addition, QA inactivation mainly contributed to minimizing the cell adhesion capacity. Consequently, the membrane fouling was significantly declined, and the final normalized water flux was promoted higher than 20% with the synergistic effect of electrorepulsion and QA inactivation. This work provides a unique long-lasting strategy to mitigate membrane biofouling.

Overview of VBNC, a survival strategy for microorganisms

Microorganisms are exposed to a wide variety of stress factors in their natural environments. Under that stressful conditions, they move into a viable but nonculturable (VBNC) state to survive and maintain the vitality. At VBNC state, microorganisms cannot be detected by traditional laboratory methods, but they can be revived under appropriate conditions. Therefore, VBNC organisms cause serious food safety and public health problems. To date, it has been determined that more than 100 microorganism species have entered the VBNC state through many chemical and physical factors. During the last four decades, dating from the initial detection of the VBNC condition, new approaches have been developed for the induction, detection, molecular mechanisms, and resuscitation of VBNC cells. This review evaluates the current data of recent years on the inducing conditions and detection methods of the VBNC state, including with microorganisms on the VBNC state, their virulence, pathogenicity, and molecular mechanisms.