The fate and behavior mechanism of antibiotic resistance genes and microbial communities in anaerobic reactors treating oxytetracycline manufacturing wastewater

Enhancing anaerobic digestion performance of oxytetracycline-laden wastewater through micro-nano bubble ozonation pretreatment

This study investigated the potential of micro-nano bubble (MNB) ozonation pretreatment to eliminate oxytetracycline (OTC) from wastewater and improve subsequent anaerobic digestion (AD) performance. The findings revealed that MNB ozonation achieved efficient OTC oxidation (>99 % in 60 min), and significantly enhanced methane production by 51 % compared to conventional ozonation (under 30 min of pretreatment). Additionally, MNB ozonation resulted in a decrease in the soluble chemical oxygen demand and reduced volatile fatty acid accumulation compared to conventional ozonation. Furthermore, the study sheds light on the profound impact of OTC and its oxidation by-products on the sludge microbiome. Exposure to OTC and its oxidation by-products resulted in alterations in extracellular polymeric substances composition and led to significant shifts in microbial community structure. This study highlights the promise of MNB ozonation as an effective approach for pharmaceutical pollutant removal and the optimization of AD performance in wastewater treatment, with implications for improved environmental sustainability.

Different fates of extracellular and intracellular antibiotic resistance genes in flocs, granular and biofilm nitrification systems under the stress of acetaminophen

The spread of antibiotic resistance genes (ARGs), including intracellular ARGs (i-ARGs) and extracellular ARGs (e-ARGs), has become a global problem that cannot be ignored. This study clarified the fates of e-ARGs and i-ARGs in floc sludge reactor (FS), granular sludge reactor (GS) and biofilm reactor (BF) under the stress of acetaminophen (APAP). The results showed that the risk of ARGs transmission, especially for e-ARGs, in FS and BF could increase with the increasing times of APAP treatment, except for that in GS. The fates of i-ARGs in three different systems were similar, which were mainly clustered as the efflux pumps mechanism. The secretion and disintegration of extracellular polymeric substances mainly affected the fates of e-ARGs. In the three systems, the complexity of network relationships between ARGs and microbial communities was FS, GS and BF. Partial least-squares path model analysis indicated that bacterial community directly contributed to the variations of e-ARGs and i-ARGs under APAP treatment in the three systems, playing a leading role. And i-ARGs and protein secondary structure showed direct effects on e-ARGs. This study indicated that e-ARGs in complex systems were more susceptible to be influenced, which should be paid more attention to prevent further propagation of ARGs.

Unravelling the resilience of magnetite assisted granules to starvation and oxytetracycline stress

Starvation and antibiotics pollution are two frequent perturbations during breeding wastewater treatment process. Supplying magnetite into anaerobic system has been proved efficient to accelerate microbial aggregates and alleviate the adverse effect caused by process disturbance. Nevertheless, whether these magnetite-based granules are still superior over normal granules after a long-term starvation period remains unknown, the responsiveness of these granules to antibiotics stress is also ambiguous. In current study, we investigated the resilience of magnetite-based anaerobic granular sludge (AnGS) to starvation and oxytetracycline (OTC) stress, by unravelling the variations of reactor performance, sludge properties, ARGs dissemination and microbial community. Compared with the AnGS formed without magnetite, the magnetite assisted AnGS appeared more robust defense to starvation and OTC stress. With magnetite supplement, the average methane yield after starvation recovery, 50 mg/L and 200 mg/L OTC stress was enhanced by 48.95%, 115.87% and 488.41%, respectively, accompanied with less VFAs accumulation, improved tetracycline removal rate (76.3-86.6% vs. 51.0-53.5%) and higher ARGs reduction. Meanwhile, magnetite supplement effectively ameliorated the potential sludge breakage by triggering more large granules formation. Trichococcus was considered an important impetus in maintaining the stability of magnetite-based AnGS process. By inducing more syntrophic methanogenesis partnerships, especially for hydrogenotrophic methanogenesis, magnetite ensured the improved reactor performance and stronger resilience at stress conditions.

Copper in different forms and tetracycline affect behavior and risk of antibiotic resistome in thermophilic anaerobic digestion of cattle manure

The metagenomics-based behavior and risk of antibiotic resistance genes (ARGs) were investigated during cattle manure thermophilic anaerobic digestion with tetracycline and copper, namely, bulk-copper oxide, nano-copper oxide, and copper sulfate, which are common feed additives. Although bulk-copper oxide reduced ARGs' diversity, it enriched high-risk ARGs the most than the other two copper species, while copper sulfate could strongly mitigate the ARG risk by decreasing their abundances. Compared to corresponding individual effects, copper and tetracycline combinations may decrease ARGs' co-occurrence potential by 22.0%, and particularly, tetracycline combined separately with copper sulfate and nano-copper oxide reduces the ARGs' risk in abundance (by 7.2%) and human health (by 4.0%). These were mainly driven by bioavailable copper, volatile fatty acids, and pH, as well as the main potential hosts in phyla Firmicutes, Coprothermobacterota, and Euryarchaeota. Notably, the twin risks of pathogenicity and ARGs should be emphasized due to the ARGs' positive correlation with human pathogens of Clostridioides difficile and Arcobacter peruensis. These findings are important for understanding the potential ARGs' risk in treatments of livestock wastes containing feed additives of different sizes and speciation.

Monitoring Longitudinal Trends and Assessment of the Health Risk of Shigella flexneri Antimicrobial Resistance

Shigella flexneri infection is the main cause of diarrhea in humans worldwide. The emergence of antimicrobial resistance (AMR) of S. flexneri is a growing public health threat worldwide, while large-scale studies monitoring the longitudinal AMR trends of isolates remain scarce. Here, the AMR gene (ARG) profiles of 717 S. flexneri isolates from 1920 to 2020 worldwide were determined. The results showed that the average number of ARGs in isolates has increased significantly, from 19.2 ± 2.4 before 1970 to 29.6 ± 5.3 after 2010. In addition, mobile genetic elements were important contributors to ARGs in S. flexneri isolates. The results of the structural equation model showed that the human development index drove the consumption of antibiotics and indirectly promoted the antibiotic resistance. Finally, a machine learning algorithm was used to predict the antibiotic resistance risk of global terrestrial S. flexneri isolates and successfully map the antibiotic resistance threats in global land habitats with over 80% accuracy. Collectively, this study monitored the longitudinal AMR trends, quantitatively surveilled the health risk of S. flexneri AMR, and provided a theoretical basis for mitigating the threat of antibiotic resistance.

A sludge bulking wastewater treatment plant with an oxidation ditch-denitrification filter in a cold region: bacterial community composition and antibiotic resistance genes

Bacterial community structure of activated sludge directly affects the stable operation of WWTPS, and these bacterial communities may carry a variety of antibiotic resistance genes (ARGs), which is a threat to the public health. This study employed 16S rRNA gene sequencing and metagenomic sequencing to investigate the bacterial community composition and the ARGs in a sludge bulking oxidation ditch-denitrification filter WWTP in a cold region. The results showed that Trichococcus (20.34%), Blautia (7.72%), and Faecalibacterium (3.64%) were the main bacterial genera in the influent. The relative abundances of norank_f_Saprospiraceae and Candidatus_Microthrix reached 10.24% and 8.40%, respectively, in bulking sludge, and those of norank_f_Saprospiraceae and Candidatus_Microthrix decreased to 6.56 and 7.10% after the anaerobic tank, indicating that the anaerobic tank had an inhibitory effect on filamentous bacteria. After 20 mJ/cm² UV disinfection, about 540 bacterial genera, such as Romboutsia (7.99%), Rhodoferax (7.98%), and Thermomonas (4.13%), could still be detected in the effluent. The ARGs were 345.11 ppm in the influent and 11.20 ppm in the effluent; 17 subtypes, such as sul1, msrE, aadA5, ErmF, and tet(A), could be detected throughout the entire process. These ARG subtypes were persistent ARGs with a high health risk. Network analysis indicated that the changes in filamentous bacteria norank_f_Saprospiraceae abundance mainly contributed to the abundance shift of MexB, and Acinetobacter mainly increased the abundance of drfA1. These results above will provide theoretical support for the sludge bulking and ARGs controls of WWTPs in cold regions.

A review of antibiotics and antibiotic resistance genes (ARGs) adsorption by biochar and modified biochar in water

Antibiotics have been used in massive quantities for human and animal medical treatment, and antibiotic resistance genes (ARGs) are of great concern worldwide. Antibiotics and ARGs are exposed to the natural environment through the discharge of medical wastewater, causing great harm to the environment and human health. Biochar has been widely used as a green and efficient adsorbent to remove pollutants. However, pristine and unmodified biochars are not considered sufficient and efficient to cope with the current serious water pollution. Therefore, researchers have chosen to improve the adsorption capacity of biochar through different modification methods. To have a better understanding of the application of modified biochar, this review summarizes the biochar modification methods and their performance, particularly, molecular imprinting and biochar aging are outlined as new modification methods, influencing factors of biochar and modified biochar in adsorption of antibiotics and ARGs and adsorption mechanisms, wherein adsorption mechanism of ARGs on biochar is found to be different than that of antibiotics. After that, the directions of biochar and modified biochar worthy of research and the issues that need attention are proposed. It can be noted that under the current dual carbon policy, biochar may have wider application prospects in future.

Distinct effects of typical sludge pretreatment approaches on the antibiotic resistance genes variations, associated bacterial community dynamics and metabolic activities during anaerobic fermentation process

Anaerobic fermentation is effective for waste activated sludge (WAS) disposal to realize resource generation and pollutants reduction, and various pretreatments were commonly applied to improve the performance. This work mainly investigated the effects of typical WAS pretreatment approaches on the antibiotic resistance genes (ARGs, as emerging contaminants) removal during anaerobic fermentation processes and unveiled the underlying mechanisms. The results indicated that all the pretreatment strategies exhibited evident effects on the overall ARGs removal with the order of Fe²⁺ activated persulfate (PS/Fe²⁺) > pH 10 > Ultrasonication > Heat, and showed selective removal tendency for the specific ARGs (namely easily removed (aadA1 and sul1) and persistent ARGs). Mechanistic analysis demonstrated that the pretreatments disrupted the extracellular polymeric substances (EPS) and rose the cell membrane permeability (particularly for PS/Fe²⁺ and Heat). Then the increased ARGs release benefitted the subsequent reduction of mobile genetic elements (MGEs) and extracellular ARGs (especially for PS/Fe²⁺ and pH10), resulting the ARGs attenuation. Pretreatments significantly shifted the microbial community structure and the abundances of potential ARGs hosts (i.e., Sulfuritalea, and Denitratisoma). Also, the different pretreatments exhibited distinct effects on the microbial metabolic traits related with ARGs proliferation (i.e., ABC transporters, two-component system and bacterial secretion systems), which also contributed to the ARGs attenuations during WAS fermentation. The partial least-squares path modeling (PLS-PM) analysis indicated that the bacterial community (total effects = 0.968) was key factor determining ARGs fates.

Structure and function response of bacterial communities towards antibiotic contamination in hyporheic zone sediments

Bacterial communities are crucial for processing and degrading contaminants in hyporheic zones (HZ). However, the effects of antibiotics on HZ bacterial communities have seldom been addressed. Here, using MiSeq 16S amplicon sequencing technology, the effects of acute exposure to Enrofloxacin, Sulfathiazole, Tetracycline hydrochloride, and Penicillin V potassium on HZ bacterial communities were investigated. Results revealed that HZ sediment communities responded differently to different classes of antibiotics, reflecting the distinct selection stress of antibiotics on HZ bacterial communities. Besides, HZ communities from the locations with more severe antibiotic contamination backgrounds (∼150 μg kg^-1) were more resistant towards antibiotic treatment. Compared with small/non-significant changes in HZ community diversity and composition treated with ng L^-1∼ug L^-1 level antibiotics compared to the control group, treatments with antibiotics over mg L^-1 level significantly reduced the diversity and changed the structures of HZ bacterial communities, and enhanced the resistance of the community to antibiotics by enriching antibiotic resistant bacteria. The exposure to mg L^-1 level antibiotics also changed community functions by restricting the growth of functional bacteria, such as ammonia oxidizing bacteria (AOB) Nitrosomonas, resulting in ammonia accumulation in sediments. The results implied that at field-relevant concentrations, there was no or minor effect of antibiotics on HZ bacterial community structure and functions, and only those areas with high antibiotic concentrations would have effects.

Influence of anthropogenic disturbances on antibiotic resistance gene distributions along the Minjiang River in Southeast China

River-reservoir systems have become ubiquitous among modern global aquatic environments due to the widespread construction of dams. However, little is known of antibiotic resistance gene (ARG) distributions in reservoir-river systems experiencing varying degrees of anthropogenic impacts. Here, the diversity, abundance, and spatial distribution of ARGs were comprehensively characterized along the main stem of the Minjiang River, a typical subtropic reservoir-river system in Southeast China using high-throughput quantitative PCR. A total of 252 ARG subtypes were detected from twelve sampling sites that were dominated by aac(3)-Via, followed by czcA, blaTEM, and sul1. Urban river waters (sites S9-S12) harbored more diverse ARGs than did the reservoir waters (sites S1-S7), indicating more serious antibiotic resistance pollution in areas with larger population densities. Dam construction could reduce the richness and absolute abundance of ARGs from upstream (site S7) to downstream (site S8). Urban river waters also harbored a higher proportion of mobile genetic elements (MGEs), suggesting that intensive human activities may promote ARG horizontal gene transfers. The mean relative abundance of Proteobacteria that could promote antibiotic resistance within microbial communities was also highest in urban river waters. Variance partitioning analysis indicated that MGEs and bacterial communities could explain 67.33%, 44.7%, and 90.29% of variation in selected ARGs for the entire watershed, aquaculture waters, and urban river waters, respectively. These results further suggest that urban rivers are ideal media for the acquisition and spread of ARGs. These findings provide new insights into the occurrence and potential mechanisms determining the distributions of ARGs in a reservoir-river system experiencing various anthropogenic disturbances at the watershed scale.

Antibiotics in anaerobic digestion: Investigative studies on digester performance and microbial diversity

The ever-increasing consumption of antibiotics in both humans and animals has increased their load in municipal and pharmaceutical industry waste and may cause serious damage to the environment. Impact of antibiotics on the performance of commercially used anaerobic digesters in terms of bioenergy output, antibiotics' removal and COD removal have been compared critically with a few studies indicating >90% removal of antibiotics. AnMBR performed the best in terms of antibiotic removal, COD removal and methane yield. Most of the antibiotics investigated have adverse effects on microbiome associated with different stages and methane generation pathways of AD which has been assessed using high throughput technologies like metatranscriptomics, metaproteomics and flow cytometry. Perspectives have been given for understanding the fate and elimination of antibiotics from AD. The challenge of optimization and process improvement needs to be addressed to increase efficiency of the anaerobic digesters.

Antibacterial Resistance Pattern in Clinical and Non-clinical Bacteria by Phenotypic and Genotypic Assessment

Bacterial infections represent a very serious problem that threatens human health, antibiotics were designed to attack the causative agents of infectious diseases, but some bacterial pathogens became virulent and resistant to antibiotics by different mechanisms, resistance genes represented one of those mechanisms. This study attempts to screen the existence of five different resistance genes (mecA, TEM, FemA, MexD, and AmpC) among 25 bacterial isolates divided into two groups the first was non-clinical bacterial type strains including Bacillus subtilis, Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Salmonella typhi, and the other group includes some clinical bacterial isolates. Evaluation of their susceptibilities to different 12 antibiotic discs and attempting to find the relationship between genotype and phenotype assessment. Different responses were reported which varied from slightly susceptible to multidrug-resistant such as P. aeruginosa and K. pneumonia which could be considered as multidrug-resistant strains. Therefore, detection of resistance gene became crucial and critical to recognize the mechanism of resistance, five pairs of primers were included to investigate five responsible genes belonging to beta-lactamases, efflux pump, and methicillin resistance. Conclusively, the PCR technique is a very accurate tool to check the genetic resistance whether being expressed to phenotype or not. Moreover, the clinical bacterial isolates appeared more resistant that reflecting the impact of the surrounding environment on bacterial behavior.