Chlorination (but Not UV Disinfection) Generates Cell Debris that Increases Extracellular Antibiotic Resistance Gene Transfer via Proximal Adsorption to Recipients and Upregulated Transformation Genes

Abstract

To advance the understanding of antibiotic resistance propagation from wastewater treatment plants, it is important to elucidate how different effluent disinfection processes affect the dissemination of predominantly extracellular antibiotic resistance genes (eARGs). Here, we show that, by facilitating proximal adsorption to recipient cells, bacterial debris generated by chlorination (but not by UV irradiation) increases the natural transformation frequency of their adsorbed eARG by 2.9 to 7.2fold relative to free eARGs. This is because chlorination increases the bacterial surface roughness by 1.1 to 6.7-fold and the affinity toward eARGs by 1.6 to 5.8-fold, and 98% of the total eARGs released after chlorination were adsorbed to cell debris. In contrast, UV irradiation released predominantly free eARGs with 18% to 56% lower transformation frequency. The collision theory indicates that the ARG donor−recipient collision frequency increased by 35.1-fold for eARGs adsorbed onto chlorination-generated bacterial debris, and the xDLVO model infers a 29% lower donor−recipient contact energy barrier for these ARGs. Exposure to chlorinationgenerated bacterial debris also upregulated genes associated with natural transformation in Vibrio vulnificus (e.g., tfoX encoding the major activator of natural transformation) by 2.6 to 5.2-fold, likely due to the generation of chlorinated molecules (5.1-fold higher Cl content after chlorination) and persistent reactive species (e.g., carbon-centered radicals) on bacterial debris. Increased proximal eARG adsorption to bacterial debris was also observed in the secondary effluent after chlorination; this decreased eARG decay by 64% and increased the relative abundance of ARGs by 7.2-fold. Overall, this study highlights that different disinfection approaches can result in different physical states of eARGs that affect their resulting dissemination potential via transformation.

Bacteria and Virus Inactivation: Relative Efficacy and Mechanisms of Peroxyacids and Chlor(am)ine

“…Moreover, the interaction mechanisms between POAs and bacteria have not been compared with those of chlorine. It has been reported that strong oxidants with low selectivity (e.g., free chlorine − and ozone ,, ) damage the cell surfaces and induce cell lysis, which in turn gives rise to release of intracellular polymeric substances (IPS) (serving as important DBP precursors and membrane foulants) and intracellular antibiotic resistance genes (iARGs). − Dukan et al reported that free chlorine was easily consumed by extracellular polymeric substances (EPS) or IPS and, hence, was more difficult to accumulate inside the cell and cause intracellular damage . In contrast, selective oxidants like PAA, with low reactivity with cell membrane and EPS, may diffuse through intact membrane and become accumulated intracellularly, while leaving the bacteria in viable but nonculturable states (VBNC). − To date, a systematic comparison between POAs and chlorine has not been demonstrated at a cellular level to evaluate their inactivation mechanisms.…”

Phenotypic and Transcriptional Responses of Pseudomonas aeruginosa Biofilms to UV-C Irradiation via Side-Emitting Optical Fibers: Implications for Biofouling Control

“…Biofilms in water systems can cause fouling and microbially induced corrosion (MIC), and pathogenic microorganisms harbored within biofilms (e.g., Legionella pneumophila ) pose human health risks; these impacts sum to $3 trillion per year in costs worldwide . Ultraviolet-C (UV-C) irradiation from light-emitting diodes (LEDs) is a chemical-free process that is highly biocidal to planktonic pathogens and has been proven to minimize biofilm formation on surfaces. − However, delivering UV-C light to complex surfaces (e.g., drinking water pipes, cooling tower basins, point-of-use devices, biomedical devices) is difficult because optical obstructions lower the UV-C light irradiance from the design value, making the actual UV-C irradiation insufficient to minimize biofilm formation on surfaces …”

“…3−5 However, delivering UV-C light to complex surfaces (e.g., drinking water pipes, cooling tower basins, point-of-use devices, biomedical devices) is difficult because optical obstructions lower the UV-C light irradiance from the design value, making the actual UV-C irradiation insufficient to minimize biofilm formation on surfaces. 6 Previous research has shown that UV-C irradiation can reduce the level of biofilm formation. Torkzadeh et al concluded that UV-C at 254 nm and 50 μW/cm 2 reduces biofilm formation at 20 °C by 95% over 48 h; an even lower UV-C irradiance is required to achieve the same reduction at low temperature (<10 °C) due to the lower bacterial growth rate.…”

Highly recyclable and stable CdS-alginate hydrogel beads towards prevention of oxidative release of nanoparticles in complete photocatalytic disinfection of multidrug-resistant Escherichia coli

“…[1][2][3] An effective disinfection method is necessary to protect the environment and the general population from antibiotic-resistant harmful bacteria prevalent in wastewater. 4,5 A variety of techniques, including ozone treatment, ultrasound, adsorption, and membrane-based filtration, have been devised by researchers to remove ARB from aqueous solutions. 6 In particular, photodynamic inactivation using photosensitizers has been steadily studied over the past decade to solve these problems and protect water sources.…”