Occurrence of E. coli and antibiotic-resistant E. coli in the southern watershed of Lake Biwa, including in wastewater treatment plant effluent and inflow rivers

Aquatic photochemistry for different dissociation forms of cephalosporin antibiotics: Degradation kinetics, products and photo-modified toxicity

Cephalosporin antibiotics (CFs) with ionizable groups (-COOH and -NHn) are widely detected as emerging micropollutants that pose potential environmental risks to aquatic systems, but few studies have revealed their multivariate photochemical transformation behavior in sunlight-irradiated surface waters. In this study, the apparent photodegradation, photo-oxidation towards reactive oxygen species (ROS, •OH and 1O2), and photo-modified toxicity were investigated for the four ionizable CFs: cefoxitin (CFX), cephalothin (CEF), cefoperazone (CFP) and cefazolin (CFZ). Under simulated sunlight irradiation (λ > 290 nm), their multivariate photo-transformation kinetics varied as a function of pHs and the dominant protonated states of the CF in question (H2CFs+, HCFs0 and CFs-). Based on competition kinetics and matrix deconvolution methods, the apparent photolytic rate constants (ki) of different dissociation forms were found to decrease gradually from H2CFs+ to CFs- then to HCFs0, which was dominated by the changing cumulative light absorption (∑(Lλελ,i)) for the different dissociated forms. Interestingly, it was observed that the H2CFs+ or CFs- exhibited higher reactivities towards •OH, while CFs- demonstrated the fastest reaction with 1O2. Using the theoretical derivation, the determined environmental half-lives of the CFs in sunlight-irradiated surface waters were closely dependent on the water pHs and multiple photochemical reaction types. In most cases, apparent photodegradation contributes more than ROS mediated photooxidation to the overall photo-transformation of CFs. The product identification using HPLC-MS/MS indicated that the photodegradation pathways mainly involved photoinduced hydrolysis of the β-lactam ring, cleavage of the side-chain, and decarboxylation. Based on the bioassay to Vibrio fischeri, the most CFs showed photo-enhanced toxicity, which was verified by the ECOSAR assessment, raising concerns about the formation and accumulation of more toxic intermediates. These results are of significance to better assessing the photochemical persistence and risk of the CFs in the aquatic systems and wastewater treatment.

Detection and collection of shiga toxin-producing Escherichia coli using foam concentration without membrane filtration

Information on Shiga toxin-producing Escherichia coli (STEC) in river water is scarce, and it is essential to understand its actual status in river water. This study investigated a method for the highly efficient recovery of STEC from river water in its active state by combining a coagulation and foam concentration and a selective medium. The method was applied to three rivers, and STEC-positive Escherichia coli (E. coli) were obtained from all rivers. Ten E. coli harboring one of the pathogenic genes (stx2, eae) were detected in the Oyodo River's upstream and midstream and the Kaeda River's midstream. Furthermore, antimicrobial agent susceptibility testing was performed on these ten strains using ten antimicrobial agents. Nine strains showed intermediate resistance to at least one antibiotic, and one was multidrug-resistant. This study's coagulation and foam concentration and selective medium detection methods can efficiently collect STEC in river water and recover it in an active state without conventional membrane filtration. Isolating and cultivating this STEC strain will provide crucial information for antimicrobial agent susceptibility testing, target gene testing, and whole-genome analysis.

Microplastics Exacerbated Conjugative Transfer of Antibiotic Resistance Genes during Ultraviolet Disinfection: Highlighting Difference between Conventional and Biodegradable Ones

Microplastics (MPs) have been confirmed as a hotspot for antibiotic resistance genes (ARGs) in wastewater. However, the impact of MPs on the transfer of ARGs in wastewater treatment remains unclear. This study investigated the roles and mechanisms of conventional (polystyrene, PS) and biodegradable (polylactic acid, PLA) MPs in the conjugative transfer of ARGs during ultraviolet disinfection. The results showed that MPs significantly facilitated the conjugative transfer of ARGs compared with individual ultraviolet disinfection, and PSMPs exhibited higher facilitation than PLAMPs. The facilitation effects were attributed to light shielding and the production of reactive oxygen species (ROS) and nanoplastics from ultraviolet irradiation of MPs. The light shielding of MPs protected the bacteria and ARGs from ultraviolet inactivation. More importantly, ROS and nanoplastics generated from irradiated MPs induced intracellular oxidative stress on bacteria and further increased the cell membrane permeability and intercellular contact, ultimately enhancing the ARG exchange. The greater fragmentation of PSMPs than PLAMPs resulted in a higher intracellular oxidative stress and a stronger enhancement. This study highlights the concerns of conventional and biodegradable MPs associated with the transfer of ARGs during wastewater treatment, which provides new insights into the combined risks of MPs and ARGs in the environment.

Prevalent and Drug-Resistant Phenotypes and Genotypes of Escherichia coli Isolated from Healthy Cow's Milk of Large-Scale Dairy Farms in China

Escherichia coli is a common cause of mastitis in dairy cows, which results in large economic losses to the livestock industry. The aim of this study was to investigate the prevalence of E. coli in raw milk in China, assess antimicrobial drug susceptibility, and identify key antibiotic resistance genes carried by the isolates. In total, 350 raw milk samples were collected from large-scale farms in 16 provinces and cities in six regions of China to assess the resistance of E. coli isolates to 14 antimicrobial drugs. Among the isolates, nine resistance genes were detected. Of 81 E. coli isolates (23.1%) from 350 raw milk samples, 27 (33.3%) were multidrug resistant. Antimicrobial susceptibility testing showed that the 81 E. coli isolates were resistant to 13 (92.9%) of the 14 antibiotics, but not meropenem. The resistance gene blaTEM was highly distributed among the 27 multidrug-resistant isolates with a detection rate of 92.6%. All isolates carried at least one resistance gene, and 19 patterns of resistance gene combinations with different numbers of genes were identified. The most common gene combinations were the one-gene pattern blaTEM and the three-gene pattern blaTEM-blaPSE-blaOXA. The isolation rate of E. coli in raw milk and the identified resistance genes provide a theoretical basis for the rational use of antibiotics by clinical veterinarians.

A One Health exploration of antimicrobial resistance in Escherichia coli originated from urban and rural lakes ecosystem

Antimicrobial resistance (AMR) has become one of the most serious threats to One Health. Aquatic environments are an ideal non-clinical AMR reservoir and can act as a key battlefront for tackling the AMR. However, AMR data using the One Health approach remain scarce in aquatic environments worldwide. Here, we extensively assessed AMR in Escherichia coli isolated from urban and rural lake ecosystems using the One Health perspective. A total of 162 E. coli isolates obtained from lakes were tested against 25 antimicrobials using an in-vitro antimicrobial susceptibility testing method. A low (2%) to moderate (45%) drug resistance rate was found for all antimicrobials used in human/veterinary medicine or animal/plant agriculture. However, <80% E. coli isolates exhibited multidrug resistance (MDR) phenotype to highly important (amikacin, gentamicin, trimethoprim) or critically important (amoxicillin, ampicillin, colistin) drugs of both human and veterinary medicine. Of concern, >50% of E. coli isolates exhibited MDR to drugs used as last-resorts (chloramphenicol, colistin) or as frontline (nitrofurantoin, sulfamethoxazole, ampicillin, gentamicin) against E. coli infections. In conclusion, the presence of MDR E. coli strains in urban or rural lake ecosystems highlights their possible role as AMR reservoirs with potential One Health risks.

Ubiquitous nanocolloids suppress the conjugative transfer of plasmid-mediated antibiotic resistance in aqueous environment

Nanocolloids (Nc) are widespread in natural water environment, whereas the potential effects of Nc on dissemination of antibiotic resistance remain largely unknown. In this study, Nc collected from the Yellow River in Henan province was tested for its ability to influence the conjugative transfer of resistant plasmid in aqueous environment. The results revealed that the conjugative transfer of RP4 plasmid between Escherichia coli was down-regulated by 52%-91% upon exposure to 1-10 mg/L Nc and the reduction became constant when the dose became higher (20-200 mg/L). Despite the exposure of Nc activated the anti-oxidation and SOS response in bacteria through up-regulating genes involved in glutathione biosynthesis and DNA recombination, the inhibition on the synthesis and secretion of extracellular polysaccharide induced the prevention of cell-cell contact, leading to the reduction of plasmid transfer. This was evidenced by the decreased bacterial adhesion and lowered levels of genes and metabolites relevant to transmembrane transport and D-glucose phosphorylation, as clarified in phenotypic, transcriptomics and metabolomics analysis of E. coli. The significant down-regulation of glycolysis/gluconeogenesis and TCA cycle was associated with the shortage of ATP induced by Nc. The up-regulation of global regulatory genes (korA and trbA) and the reduction of plasmid genes (trfAp, trbBp, and traG) expression also contributed to the suppressed conjugation of RP4 plasmid. The obtained findings remind that the role of ubiquitous colloidal particles is nonnegligible when practically and comprehensively assessing the risk of antibiotic resistance in the environment.

Significant Factors for Modelling Survival of Escherichia coli in Lake Sediments

Currently available numerical models that describe the fecal contamination of aquatic environments using Escherichia coli as an indicator bacterium did not consider its survival in sediments. We conducted a series of comparative experiments to reveal the independent and interactive effects of sediment factors, including temperature, pH, water-extractable total dissolved solids (TDSs), coexisting microbes, and sampling sites, in lake environments on E. coli survival. In experiments, E. coli survival was observed by controlling any two factors at a time. Consequently, the decrease in pH and presence of coexisting microbes enhanced E. coli die-off, whereas the addition of water-extractable TDSs promoted its growth. To select factors to be considered for modelling E. coli survival in sediments, the independent effects of each factor and the interaction effect of the two factors were statistically compared based on their effect sizes (η2). As a result, pH (η2 = 59.5-89.0%) affected E. coli survival most significantly, followed by coexisting microbes (1.7-48.4%). Among the interactions affecting E. coli survival, including pH or coexisting microbes-which had larger independent effects-relatively larger statistically significant interactions were observed between pH and coexisting microbes (31.1%), coexisting microbes and water-extractable TDSs (85.4%), and coexisting microbes and temperature (26.4%).

Comprehensive Assessment of Multidrug-Resistant and Extraintestinal Pathogenic Escherichia coli in Wastewater Treatment Plant Effluents

Multidrug-resistant (MDR) Escherichia coli poses a significant threat to public health, contributing to elevated rates of morbidity, mortality, and economic burden. This study focused on investigating the antibiotic resistance profiles, resistance and virulence gene distributions, biofilm formation capabilities, and sequence types of E. coli strains resistant to six or more antibiotic classes. Among 918 strains isolated from 33 wastewater treatment plants (WWTPs), 53.6% (492/918) demonstrated resistance, 32.5% (298/918) were MDR, and over 8% (74/918) were resistant to six or more antibiotic classes, exhibiting complete resistance to ampicillin and over 90% to sulfisoxazole, nalidixic acid, and tetracycline. Key resistance genes identified included sul2, blaTEM, tetA, strA, strB, and fimH as the predominant virulence genes linked to cell adhesion but limited biofilm formation; 69% showed no biofilm formation, and approximately 3% were strong producers. Antibiotic residue analysis detected ciprofloxacin, sulfamethoxazole, and trimethoprim in all 33 WWTPs. Multilocus sequence typing analysis identified 29 genotypes, predominantly ST131, ST1193, ST38, and ST69, as high-risk clones of extraintestinal pathogenic E. coli. This study provided a comprehensive analysis of antibiotic resistance in MDR E. coli isolated from WWTPs, emphasizing the need for ongoing surveillance and research to effectively manage antibiotic resistance.

Antibiotic resistance genes profile in the surface sediments of typical aquaculture areas across 15 major lakes in China

Aquatic farming is considered as a major source of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) for the natural environment of the lakes. ARB and ARGs in the natural environment have increased quickly because of the human activities. Here, we have profiled the diversity and abundance of ARGs in sediments from the typical aquaculture areas around 15 major lakes in China using PCR and qPCR, and further assessed the risk factor shaping the occurrence and distribution of ARGs. And class 1, 2 and 3 integrons were initially detected by PCR with specific primers. ARGs were widely distributed in the lakes: Weishan Lake and Poyang Lake showed high diversity of ARGs, followed by Dongting Lake, Chao Lake and Tai Lake. Generally, the ARGs in the Middle-Lower Yangtze Plain were more abundant than those in the Qinghai-Tibet Plateau. Tetracycline resistance genes (tet(C), tet(A) & tet(M)) were prominent in sediments, and the next was AmpC β-lactamase gene group BIL/LAT/CMY, and the last was the genes resistance to aminoglycoside (strA-strB). Partial least squares path modeling analysis (PLS-PMA) revealed that livestock had a significant direct effect on the distribution of ARGs in lakes, and population might indirectly influence the profiles of ARGs by affecting the scale of livestock and aquaculture. The detectable rate of class 1, 2 and 3 integrons were 80%, 100% and 46.67%, respectively. The prevalence of integrons might play a key role in promoting more frequent horizontal gene transfer (HGT) events, resulting in the environmental mobilization and dissemination of ARGs between bacteria.

Mobile genetic elements affect the dissemination of antibiotic resistance genes (ARGs) of clinical importance in the environment

The prevalence of antibiotic resistance genes (ARGs) in the environment is a quintessential One Health issue that threats both human and ecosystem health; however, the source and transmission of ARGs, especially clinically important ARGs (CLIARGs), in the environment have not yet been well studied. In the present study, shotgun metagenomic approaches were used to characterize the microbiome, resistome, and mobilome composition in human feces and six different environment sample types in South China. Overall, the resistome harbored 157 CLIARGs, with specific ARG hotspots (e.g., human feces, wastewater treatment plants, livestock manure and wastewater) excreting significantly higher abundance of CLIARGs compared with the natural environment. A redundancy analysis (RDA) was performed and revealed that the bacterial community compositions and mobile genetic elements (MGEs) explained 55.08% and 34.68% of the variations in ARG abundance, respectively, indicating that both bacterial community and MGEs are key contributors to the maintenance and dissemination of CLIARGs in the environment. The network analysis revealed non-random co-occurrence patterns between 200 bacterial genera and 147 CLIARGs, as well as between 135 MGEs and 123 CLIARGs. In addition to numerous co-shared CLIARGs among different sample types, the source tracking program based on the FEAST probabilistic model was used to estimate the relative contributions of the CLIARGs from potential sources to the natural environment. The source tracking analysis results delineated that mobilome, more than microbiome, contributed CLIARG transmission from those ARG hotspots into natural environment, and the MGEs in WWTPs seem to play the most significant role in the spread of CLIARGs to the natural environment (average contribution 32.9%-46.4%). Overall, this study demonstrated the distribution and dissemination of CLIARGs in the environment, and aimed to better inform strategies to control the spread of CLIARGs into the natural environment.

Comprehensive overview of antibiotic distribution, risk and priority: A study of large-scale drinking water sources from the lower Yangtze River

Antibiotics have attracted widespread attention around the world because they are ubiquitous in the environment and can lead to antibiotic-resistant microbes developing and pose ecotoxicological risks. In this study, we determined the spatiotemporal distributions of 39 antibiotics in 19 drinking water sources in Jiangsu area of the lower Yangtze River and attempted to identify the sources of the antibiotics and to prioritize the antibiotics. The total antibiotic concentrations in spring and fall were 234.56-6515.99 and 151.12-2562.59 ng/L, respectively. In spring, the total antibiotic concentration gradually increased from upstream to downstream. In fall, the antibiotic concentration did not markedly vary upstream to downstream (total concentrations 151.12-432.17 ng/L) excluding site S9 and S10. Analysis using a positive matrix factorization (PMF) model indicated that the antibiotics had four main sources. Pharmaceutical wastewater was the main source, contributing 34.1% and 41.2% of total antibiotics in spring and fall, respectively, and domestic wastewater was the second most important source, contributing 24.4% and 43% of total antibiotics in spring and fall, respectively. Pharmaceutical wastewater was the main source from midstream to downstream, but the other sources made different contributions in different areas because of the various ranges of human activities. An ecological risk assessment was performed. Stronger risks were posed by antibiotics in spring than fall, and fluoroquinolone antibiotics posed the strongest risks. Optimized risk quotients indicated that norfloxacin was a high-risk contaminant. An assessment of the risk of resistance development indicated that norfloxacin, ciprofloxacin, and enrofloxacin posed moderate to high risks of resistance development and should be prioritized for risk management. The results of this study are important reference data for identifying key sources of antibiotics and developing strategies to manage antibiotic contamination in similar areas.

Characterization of antibiotic resistance genes and bacteria in a municipal water resource recovery facility

Municipal water resource recovery facilities (WRRFs) are important sources of antibiotic-resistant bacteria and genes (ARB and ARGs). In this study, antibiotic-resistant total heterotrophic bacteria (THB_R ) counts (CFU/ml) cultivated from influent, effluent of activated sludge process, and outflow of disinfection unit of an urban WRRF were investigated for the presence of 16, 32, 64, and 128 μg/ml of nine antibiotics. The isolates of Pseudomonas spp., Acinetobacter spp., and Escherichia coli obtained from effluent of activated sludge process were subjected for molecular identification by detecting the 16S rRNA gene sequences. Additionally, using the polymerase chain reaction method (PCR), the isolates were investigated for the presence of bla_SHV , bla_TEM , bla_CTX-M , bla_VIM , sul1, and qnrS genes. According to the results, the abundance of THB_R counts was not significantly reduced by the biological treatment except for cefixime and sulfamethoxazole; it also increased for some antibiotics after disinfection unit. The average removal efficiency of THB_R resistant to ciprofloxacin, sulfamethoxazole, and ceftazidime were 7.9 ± 1.7%, 41.8 ± 2.1%, and 14.4 ± 6.2%, respectively. Also, all the tested isolates were resistant to at least four antibiotics. For all antibiotics, the resistance ratio (THB_R /THB) significantly increased in the effluent and after chlorination unit. Among 12 resistant isolates, bla_TEM and sul1 genes were the most frequently detected ones involved in 92% and 83% of the isolates, respectively. Both bla_TEM and sul1 genes were found in 100% of E. coli, and 83% and 67% of Pseudomonas spp. isolates, respectively. Further efforts are necessary to limit the transmission of ARB and ARGs from WRRFs into the environment and prevent human health threats. PRACTITIONER POINTS: The ratio of resistance significantly increased after biological treatment. Up to 40% of heterotrophic bacteria in the effluent was antibiotic resistant. bla_TEM and sul1 genes were more prevalent (92%) in all isolates of bacteria. Both bla_TEM and sul1 genes were found in 100% of E. coli isolates. Pseudomonas spp. holds bla_TEM and sul1 genes in 83% and 67% of isolates, respectively.