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.

Fungi outbreaks in water will include a series of processes, including spore aggregation, germination, biofilm, and finally present in a mixed state in the aquatic environment. More attention is paid to the control of dispersed fungal spores, however, there was little knowledge of the control of germinated spores. This study investigated the inactivation kinetics and mechanism of ultraviolet (UV) treatment for fungal spores with different germination percentages compared with dormant spores. The results indicated that the inactivation rate constants (k) of spores with 5%-45% germination were 0.0278-0.0299 cm2/mJ for Aspergillus niger and 0.0588-0.0647 cm2/mJ for Penicillium polonicum, which were lower than those of dormant spores. It suggested that germinated spores were more tolerant to UV irradiation than dormant spores, and it may be due to the defensive barrier (upregulated pigments) and some reductive substance (upregulated enoyl reductase) by absorbing UV or reacting with reactive oxygen species according to transcriptome analysis. Compared to dormant spores, the k-UV of germinated spores decreased by 18.17%-26.56% for Aspergillus niger, which was less than k-chlorine (62.33%-69.74%). A slighter decrease in k-UV showed UV irradiation can efficiently control fungi contamination, especially when dormant spores and germinated spores coexisted in actual water systems. This study indicates that more attention should be paid to germinated spores.

Wash water is circulated for use in the minimal processing industry, and inefficient disinfection methods can lead to pathogen cross-contamination. Moreover, few disinfection strategies are available for ready-to-eat fruits that do not need to be cut. In this study, the use of chlorine and ultrasound, two low-cost disinfection methods, were evaluated to disinfect winter jujube, a delicious, nutritious, and widely sold fruit in China. Ultrasound treatment (28 kHz) alone could not decrease the cross-contamination incidence of Escherichia coli O157:H7, non-O157 E. coli, and Salmonella Typhimurium, and free chlorine treatment at 10 ppm decreased the incidence from 55.00% to 5.00% for E. coli O157:H7, 65.00% to 6.67% for non-157 E. coli, and 70.00% to 6.67% for S. Typhimurium. The cross-contamination incidence was completely reduced (pathogens were not detected in sample) when the treatments were combined. The counts of aerobic mesophiles, aerobic psychrophiles, molds, yeasts, and three pathogens in the group subjected to combination treatment (28 kHz ultrasound + 10 ppm free chlorine) were significantly lower than those in the control, chlorine-treated, and ultrasound-treated groups during storage (0-7 d at 4 °C). Analysis of weight loss, sensory quality (crispness, color, and flavor), instrument color (a*/b*), soluble matter contents (total soluble solids, reducing sugar, total soluble sugar, and titratable acid), and nutritional properties (ascorbic acid and polyphenolic contents) indicated that treatment with ultrasound, chlorine, and their combination did not lead to additional quality loss compared with properties of the control. Additionally, the activities of phenylalanine ammonia-lyase and polyphenol oxidase were not significantly increased in the treatment group, consistent with the quality analysis results. These findings provide insights into disinfection of uncut ready-to-eat fruits using a minimum dose of disinfectant for cross-contamination prevention under ultrasonication. The use of ultrasound alone to decontaminate fresh produce is accompanied by a high risk of pathogen contamination, and the use of sanitizers to decrease cross-contamination incidence is recommended.

During rapid proliferation and metabolism, tumor cells show a high dependence on methionine. The deficiency of methionine exhibits significant inhibition on tumor growth, which provides a potential therapeutic target in tumor therapy. Herein, ClO2-loaded nanoparticles (fluvastatin sodium&metformin&bupivacaine&ClO2@CaSiO3@MnO2-arginine-glycine-aspatic acid (RGD) (MFBC@CMR) NPs) were prepared for synergistic chlorine treatment and methionine-depletion starvation therapy. After outer layer MnO2 was degraded in the high glutathione (GSH) tumor microenvironment (TME), MFBC@CMR NPs released metformin (Me) to target the mitochondria, thus interfering with the tricarboxylic acid (TCA) cycle and promoting the production of lactate. In addition, released fluvastatin sodium (Flu) by the NPs acted on monocarboxylic acid transporter 4 (MCT4) in the cell membrane to inhibit lactate leakage and induce a decrease of intracellular pH, further prompting the NPs to release chlorine dioxide (ClO2), which then oxidized methionine, inhibited tumor growth, and produced large numbers of Cl- in the cytoplasm. Cl- could enter mitochondria through the voltage-dependent anion channel (VDAC) channel, which was opened by bupivacaine (Bup). The disruption of Cl- homeostasis promotes mitochondrial damage and membrane potential decline, leading to the release of cytochrome C (Cyt-C) and apoptosis inducing factor (AIF) and further inducing cell apoptosis. To sum up, the pH-regulating and ClO2-loaded MFBC@CMR nanoplatform can achieve cascade chlorine treatment and methionine-depletion starvation therapy toward tumor cells, which is of great significance for improving the clinical tumor treatment effect.

Evaluating the efficacy of disinfection processes to inactivate human enteric viruses is important for the prevention and control of waterborne diseases caused by exposure to those viruses via drinking water. Here, we evaluated the inactivation of two representative human enteric viruses (adenovirus type 40 [AdV] and coxsackievirus B5 [CV]) by thermal or free-chlorine disinfection. In addition, we compared the infectivity reduction ratio of a plant virus (pepper mild mottle virus [PMMoV], a recently proposed novel surrogate for human enteric viruses for the assessment of virus removal by coagulation‒rapid sand filtration and membrane filtration) with that of the two human enteric viruses to assess the suitability of PMMoV as a human enteric virus surrogate for use in thermal and free-chlorine disinfection processes. Finally, we examined whether conventional or enhanced viability polymerase chain reaction (PCR) analysis using propidium monoazide (PMA) or improved PMA (PMAxx) with or without an enhancer could be used as alternatives to infectivity assays (i.e., plaque-forming unit method for AdV and CV; local lesion count assay for PMMoV) for evaluating virus inactivation by disinfection processes. We found that PMMoV was more resistant to heat treatment than AdV and CV, suggesting that PMMoV is a potential surrogate for these two enteric viruses with regard to thermal disinfection processes. However, PMMoV was much more resistant to chlorine treatment compared with AdV and CV (which is chlorine-resistant) (CT value for 4-log10 inactivation: PMMoV, 84.5 mg-Cl2·min/L; CV, 1.15-1.19 mg-Cl2·min/L), suggesting that PMMoV is not useful as a surrogate for these enteric viruses with regard to free-chlorine disinfection processes. For thermal disinfection, the magnitude of the signal reduction observed with PMAxx-Enhancer-PCR was comparable with the magnitude of reduction in infectivity, indicating that PMAxx-Enhancer-PCR is a potential alternative to infectivity assay. However, for free-chlorine disinfection, the magnitude of the signal reduction observed with PMAxx-Enhancer-PCR was smaller than the magnitude of the reduction in infectivity, indicating that PMAxx-Enhancer-PCR underestimated the efficacy of virus inactivation (i.e., overestimated the infectious virus concentration) by chlorine treatment. Nevertheless, among the PCR approaches examined in the present study (PCR alone, PMA-PCR or PMAxx-PCR either with or without enhancer), PMAxx-Enhancer-PCR provided the most accurate assessment of the efficacy of virus inactivation by thermal or free chlorine disinfection processes.

Chlorine is the most widely used carcass sanitizer in poultry processing in the USA. The objective of this study was to determine the effects of varying concentrations of organic matter on the susceptibility of twelve most prevalent poultry-associated Salmonella serotypes (MPPSTs) to chlorine. To mimic the microenvironment of the water used for immersion chilling, we manipulated organic matter contamination levels in pre-chilled (pH∼6, T∼4 °C) chlorinated (50 ppm) water using varying concentrations (0, 1, 2, 3, 4, and 5%) of chicken-meat-extract (CME) produced from frozen chicken carcasses. This CME-based in vitro model was challenged with ∼1 × 105 CFUs of each MPPST isolate and the bacterial survival was tested at 5, 30, 60 and 90 min post-challenge. In this model, the decimal reduction time (D90-values) of each MPPST was linearly correlated with the concentration of CME. Significant inter-serotype differences in the D90-values were observed. The results show that the pH, concentration of total- and free-chlorine were also linearly correlated with the presence of CME in a concentration-dependent manner. The findings of this study indicate that the serotype and the levels of organic matter contamination significantly influence Salmonella survival and that both variables should be included in models that predict effectiveness of chlorine treatment in immersion chilling.