Biological and physicochemical wastewater treatment processes reduce the prevalence of virulent Escherichia coli

Occurrence and Reduction of Shiga Toxin-Producing Escherichia coli in Wastewaters in the Kathmandu Valley, Nepal

Inadequately treated effluents discharged from wastewater treatment plants (WWTPs) severely affect the environment and the surrounding population. This study analyzed the presence of the Shiga toxin-producing Escherichia coli (STEC) genes, stx1, and stx2, and the E. coli gene, sfmD, in municipal WWTP A (n = 11) and B (n = 11) where the reductions were also evaluated; hospitals (n = 17), sewage treatment plants (STPs) (n = 4) and non-functional WWTPs (not-working WWTPs) (n = 5) in the Kathmandu Valley, Nepal. The sfmD gene was detected in 100% of the samples in WWTPs, hospitals, and not-working WWTPs and 50% of STP samples. The highest detection of stx1 and stx2 was shown in the WWTP influents, followed by WWTP effluents, not-working WWTP wastewater, hospital wastewater, and STP wastewater. Log10 reduction values of sfmD, stx1, and stx2 in WWTP A were 1.7 log10, 1.7 log10, 1.4 log10, whereas those in WWTP B were 0.5 log10, 0.6 log10, 0.5 log10, respectively, suggesting the ineffective treatment of STEC in the wastewater in the Kathmandu Valley. The high concentrations of the stx genes in the wastewaters suggest the increasing presence of aggressive STEC in the Kathmandu Valley, which should be a major public health concern.

Naturalized Escherichia coli in Wastewater and the Co-evolution of Bacterial Resistance to Water Treatment and Antibiotics

Antibiotic resistance represents one of the most pressing concerns facing public health today. While the current antibiotic resistance crisis has been driven primarily by the anthropogenic overuse of antibiotics in human and animal health, recent efforts have revealed several important environmental dimensions underlying this public health issue. Antibiotic resistant (AR) microbes, AR genes, and antibiotics have all been found widespread in natural environments, reflecting the ancient origins of this phenomenon. In addition, modern societal advancements in sanitation engineering (i.e., sewage treatment) have also contributed to the dissemination of resistance, and concerningly, may also be promoting the evolution of resistance to water treatment. This is reflected in the recent characterization of naturalized wastewater strains of Escherichia coli-strains that appear to be adapted to live in wastewater (and meat packing plants). These strains carry a plethora of stress-resistance genes against common treatment processes, such as chlorination, heat, UV light, and advanced oxidation, mechanisms which potentially facilitate their survival during sewage treatment. These strains also carry an abundance of common antibiotic resistance genes, and evidence suggests that resistance to some antibiotics is linked to resistance to treatment (e.g., tetracycline resistance and chlorine resistance). As such, these naturalized E. coli populations may be co-evolving resistance against both antibiotics and water treatment. Recently, extraintestinal pathogenic strains of E. coli (ExPEC) have also been shown to exhibit phenotypic resistance to water treatment, seemingly associated with the presence of various shared genetic elements with naturalized wastewater E. coli. Consequently, some pathogenic microbes may also be evolving resistance to the two most important public health interventions for controlling infectious disease in modern society-antibiotic therapy and water treatment.

Metagenomics Insights Into the Microbial Diversity and Microbiome Network Analysis on the Heterogeneity of Influent to Effluent Water

Sanitizing the water sources of local communities is important to control the spread of microbial resistance genes, especially those for water-borne illnesses. The activities of antibiotic resistance gene (ARG)-host pathogens pose a threat to public health, and it has been estimated that the infection will lead up to 10 million deaths globally by the year 2050. Hence, in this study, we aim to analyze the efficiency of our municipal wastewater treatment plant (WWTP) process in producing pathogen-free water by investigating the microbial composition between influent and effluent water sites. Shotgun metagenomics sequencing using the Illumina platform was performed on the influent and effluent samples of six different WWTP sites located in Johore, Malaysia. After raw data pre-processing, the non-redundant contigs library was then aligned against BLASTP for taxonomy profiling and the Comprehensive Antibiotic Resistance Database for ARG annotation. Interestingly, the alpha-diversity result reported that effluent site samples showed higher abundance and diverse heterogeneity compared to the influent site. The principal component analysis (PCA) and non-metric multidimensional scaling (NMDS) plots also suggested that effluent sites showed high variation in the genetic material due to loosely clustered sample plots, as compared to the tightly clustered influent samples. This study has successfully identified the top three abundant phyla in influent-Proteobacteria, Firmicutes, and Bacteroidetes-and effluent-Proteobacteria, Actinobacteria, and Bacteroidetes-water. Despite the overlap within the top three abundant phyla in influent and effluent sites (Proteobacteria and Bacteroidetes), the ARG composition heat map and drug class phenotype plot bar exhibits a general trend of a downward shift, showing the efficiency of WWTP in reducing opportunistic pathogens. Overall, it was demonstrated that our municipal WWTP efficiently eliminated pathogenic microbes from the influent water before its total discharge to the environment, though not with the total elimination of microorganisms. This metagenomics study allowed for an examination of our water source and showed the potential interaction of species and ARGs residing in the influent and effluent environment. Both microbial profile structure and co-occurrence network analysis provide integrated understanding regarding the diversity of microorganisms and interactions for future advanced water sanitation treatments.

A Biofouling Resistant Zwitterionic Polysulfone Membrane Prepared by a Dual-Bath Procedure

This study introduces a zwitterionic material to modify polysulfone (PSf) membranes formed by a dual bath procedure, in view of reducing their fouling propensity. The zwitterionic copolymer, derived from a random polymer of styrene and 4-vinylpyrridine and referred to as zP(S-r-4VP), was incorporated to the PSf solution without any supplementary pore-forming additive to study the effect of the sole copolymer on membrane-structuring, chemical, and arising properties. XPS and mapping FT-IR provided evidence of the modification. Macrovoids appeared and then disappeared as the copolymer content increased in the range 1-4 wt%. The copolymer has hydrophilic units and its addition increases the casting solution viscosity. Both effects play an opposite role on transfers, and so on the growth of macrovoids. Biofouling tests demonstrated the efficiency of the copolymer to mitigate biofouling with a reduction in bacterial and blood cell attachment by more than 85%. Filtration tests revealed that the permeability increased by a twofold factor, the flux recovery ratio was augmented from 40% to 63% after water/BSA cycles, and irreversible fouling was reduced by 1/3. Although improvements are needed, these zwitterionic PSf membranes could be used in biomedical applications where resistance to biofouling by cells is a requirement.

Antimicrobial Photodynamic Therapy in the Control of COVID-19

Antimicrobial photodynamic therapy (aPDT), using well known, safe and cost-effective photosensitizers, such as phenothiazines, e.g., methylene blue (MB), or porphyrins, e.g., protoporphyrin-IX (PP-IX), might help to mitigate the COVID-19 either to prevent infections or to develop photoactive fabrics (e.g., masks, suits, gloves) to disinfect surfaces, air and wastewater, under artificial light and/or natural sunlight.

Bacteria from the Genus Arcobacter Are Abundant in Effluent from Wastewater Treatment Plants

Pathogenic bacteria in wastewater are generally considered to be efficiently removed in biological wastewater treatment plants. This understanding is almost solely based on culture-based control measures, and here we show, by applying culture-independent methods, that the removal of species in the genus Arcobacter was less effective than for many other abundant genera in the influent wastewater. Arcobacter was one of the most abundant genera in influent wastewater at 14 municipal wastewater treatment plants and was also abundant in the "clean" effluent from all the plants, reaching up to 30% of all bacteria as analyzed by 16S rRNA gene amplicon sequencing. Metagenomic analyses, culturing, genome sequencing of Arcobacter isolates, and visualization by fluorescent in situ hybridization (FISH) confirmed the presence of the human-pathogenic Arcobacter cryaerophilus and A. butzleri in both influent and effluent. The main reason for the high relative abundance in the effluent was probably that Arcobacter cells, compared to those of other abundant genera in the influent, did not flocculate and attach well to the activated sludge flocs, leaving a relatively large fraction dispersed in the water phase. The study shows there is an urgent need for new standardized culture-independent measurements of pathogens in effluent wastewaters, e.g., amplicon sequencing, and an investigation of the problem on a global scale to quantify the risk for humans and livestock.IMPORTANCE The genus Arcobacter was unexpectedly abundant in the effluent from 14 Danish wastewater treatment plants treating municipal wastewater, and the species included the human-pathogenic A. cryaerophilus and A. butzleri Recent studies have shown that Arcobacter is common in wastewater worldwide, so the study indicates that discharge of members of the genus Arcobacter may be a global problem, and further studies are needed to quantify the risk and potentially minimize the discharge. The study also shows that culture-based analyses are insufficient for proper effluent quality control, and new standardized culture-independent measurements of effluent quality encompassing most pathogens should be considered.

Principal component analysis exploring the association between antibiotic resistance and heavy metal tolerance of plasmid-bearing sewage wastewater bacteria of clinical relevance

This paper unravels the occurrence of plasmid-mediated antibiotic resistance in association with tolerance to heavy metals among clinically relevant bacteria isolated from sewage wastewater. The bacteria isolated were identified following conventional phenotypic and/or molecular methods, and were subjected to multiple-antibiotic resistance (MAR) profiling. The isolates were tested against the heavy metals Hg²⁺, Cd²⁺, Cr²⁺ and Cu²⁺. SDS-PAGE and agarose gel electrophoretic analyses were performed, respectively, for the characterization of heavy metal stress protein and R-plasmid among the isolated bacteria. Principal component analysis was applied in determining bacterial resistance to antibiotics and heavy metals. Both lactose-fermenting ( Escherichia coli ) and non-fermenting ( Acinetobacter baumannii and Pseudomonas putida ) Gram-negative bacterial strains were procured, and showed MAR phenotypes with respect to three or more antibiotics, along with resistance to the heavy metals Hg²⁺, Cd²⁺, Cr²⁺ and Cu²⁺. The Gram-positive bacteria, Enterococcus faecalis , isolated had 'ampicillin-kanamycin-nalidixic acid' resistance. The bacterial isolates had MAR indices of 0.3-0.9, indicating their ( E. faecalis , E. coli , A. baumannii and P. putida ) origin from niches with high antibiotic pollution and human faecal contamination. The Gram-negative bacteria isolated contained a single plasmid (≈54 kb) conferring multiple antibiotic resistance, which was linked to heavy metal tolerance; the SDS-PAGE analysis demonstrated the expression of heavy metal stress proteins (≈59 and ≈10 kDa) in wastewater bacteria with a Cd²⁺ stressor. The study results grant an insight into the co-occurrence of antibiotic resistance and heavy metal tolerance among clinically relevant bacteria in sewage wastewater, prompting an intense health impact over antibiotic usage.

Abundance and Antimicrobial Resistance of Three Bacterial Species along a Complete Wastewater Pathway

After consumption, antibiotic residues and exposed bacteria end up via the feces in wastewater, and therefore wastewater is believed to play an important role in the spread of antimicrobial resistance (AMR). We investigated the abundance and AMR profiles of three different species over a complete wastewater pathway during a one-year sampling campaign, as well as including antimicrobial consumption and antimicrobial concentrations analysis. A total of 2886 isolates (997 Escherichia coli, 863 Klebsiella spp., and 1026 Aeromonas spp.) were cultured from the 211 samples collected. The bacterial AMR profiles mirrored the antimicrobial consumption in the respective locations, which were highest in the hospital. However, the contribution of hospital wastewater to AMR found in the wastewater treatment plant (WWTP) was below 10% for all antimicrobials tested. We found high concentrations (7-8 logs CFU/L) of the three bacterial species in all wastewaters, and they survived the wastewater treatment (effluent concentrations were around 5 log CFU/L), showing an increase of E. coli in the receiving river after the WWTP discharge. Although the WWTP had no effect on the proportion of AMR, bacterial species and antimicrobial residues were still measured in the effluent, showing the role of wastewater contamination in the environmental surface water.

Graphene oxide as a tool for antibiotic-resistant gene removal: a review

Environmental pollutants, including antibiotics (ATBs), have become an increasingly common health hazard in the last several decades. Overdose and abuse of ATBs led to the emergence of antibiotic-resistant genes (ARGs), which represent a serious health threat. Moreover, water bodies and reservoirs are places where a wide range of bacterial species with ARGs originate, owing to the strong selective pressure from presence of ATB residues. In this regard, graphene oxide (GO) has been utilised in several fields including remediation of the environment. In this review, we present a brief overview of resistant genes of frequently used ATBs, their occurrence in the environment and their behaviour. Further, we discussed the factors influencing the binding of nucleic acids and the response of ARGs to GO, including the presence of salts in the water environment or water pH, because of intrinsic properties of GO of not only binding to nucleic acids but also catalysing their decomposition. This would be helpful in designing new types of water treatment facilities.

Investigating the potential use of an Antarctic variant of Janthinobacterium lividum for tackling antimicrobial resistance in a One Health approach

The aim of this paper is to describe a new variant of Janthinobacterium lividum - ROICE173, isolated from Antarctic snow, and to investigate the antimicrobial effect of the crude bacterial extract against 200 multi-drug resistant (MDR) bacteria of both clinical and environmental origin, displaying various antibiotic resistance patterns. ROICE173 is extremotolerant, grows at high pH (5.5–9.5), in high salinity (3%) and in the presence of different xenobiotic compounds and various antibiotics. The best violacein yield (4.59 ± 0.78 mg·g⁻¹ wet biomass) was obtained at 22 °C, on R2 broth supplemented with 1% glycerol. When the crude extract was tested for antimicrobial activity, a clear bactericidal effect was observed on 79 strains (40%), a bacteriostatic effect on 25 strains (12%) and no effect in the case of 96 strains (48%). A very good inhibitory effect was noticed against numerous MRSA, MSSA, Enterococci, and Enterobacteriaceae isolates. For several environmental E. coli strains, the bactericidal effect was encountered at a violacein concentration below of what was previously reported. A different effect (bacteriostatic vs. bactericidal) was observed in the case of Enterobacteriaceae isolated from raw vs. treated wastewater, suggesting that the wastewater treatment process may influence the susceptibility of MDR bacteria to violacein containing bacterial extracts.

Continuous Flow-Constructed Wetlands for the Treatment of Swine Waste Water

The microbiological quality of treated waste water is always a concern when waste water is disposed to the environment. However, when treated appropriately, such water can serve many purposes to the general population. Therefore, the treatment and removal of contaminants from swine waste water by continuous flow-constructed wetlands involves complex biological, physical, and chemical processes that may produce better quality water with reduced levels of contaminants. Swine waste contains E. coli populations and other bacterial contaminants originating from swine houses through constructed wetlands, but little is known about E. coli population in swine waste water. To assess the impacts of seasonal variations and the effect of the wetland layout/operations on water quality, E. coli isolates were compared for genetic diversity using repetitive extragenic palindromic polymerase chain reaction (REP-PCR). None of the isolates was confirmed as Shiga toxin producing E. coli O157:H7 (STEC); however, other pathotypes, such as enterotoxigenic E. coli (ETEC) were identified. Using a 90% similarity index from REP-PCR, 69 genotypes out of 421 E. coli isolates were found. Our data showed that the E. coli population was significantly (p = 0.036) higher in November than in March and August in most of the wetland cells. Furthermore, there was a significant (p = 0.001) reduction in E. coli populations from wetland influent to the final effluent. Therefore, the use of continuous flow-constructed wetlands may be a good treatment approach for reducing contaminants from different waste water sources.

Improved antifouling potential of polyether sulfone polymeric membrane containing silver nanoparticles: self-cleaning membranes

A new strategy to enhance the antifouling potential of polyether sulfone (PES) membrane is presented. Chemically synthesized silver nanoparticles (AgNPs) were used to prepare a mixed-matrix PES membrane by the phase inversion technique. Primarily, AgNPs synthesis was confirmed by surface plasmon resonance at 410-430 nm using UV-Visible spectroscopy. X-ray diffraction analysis revealed that AgNPs were crystalline with a diameter of 21 ± 2 nm. Furthermore, PES membranes were characterized by energy dispersive X-ray spectroscopy to confirm the incorporation of AgNPs in membranes. Hydrophilicity of the membranes was enhanced, whereas roughness, mechanical strength and biofouling were relatively reduced after embedding the AgNPs. Antibacterial potential of AgNPs was evaluated for E. coli in the disc diffusion and colony-forming unit (CFU) count method. All of the membranes were assessed for antifouling activity by filtering a control dilution (10⁶ CFU/ml) of E. coli and by counting CFU. Anti-biofouling activity of the membrane was observed with different concentrations of AgNPs. Maximum reduction (66%) was observed in membrane containing 1.5% of AgNPs. The addition of antibiotic ceftriaxone enhanced the antibacterial effect of AgNPs in PES membranes. Our practicable antifouling strategy may be applied to other polymeric membranes which may pave the new way to achieve sustainable and self-cleaning membrane reactors on large scale.

Fluoroquinolones (FQs) in the environment: A review on their abundance, sorption and toxicity in soil

The use of fluoroquinolones (FQs) antibiotics as therapeutic agents and growth promoters is increasing worldwide; however their extensive uses are also resulting in antibiotic resistance among world communities. FQs have also become one of the major contaminants in the waste water bodies, which are not even completely removed during the treatment processes. Furthermore, their abundance in agricultural resources, such as the irrigation water, the bio-solids and the livestock manure can also affect the soil micro-environment. These antibiotics in soil tend to interact in several different ways to affect soil flora and fauna. The current review endeavors to highlight the some critical aspects of FQs prevalence in the environment. The review presents a detailed discussion on the pathways and abundance of FQs in soil. The discussion further spans the issue of sorption and FQs transformation into the soil better understand of their behavior and their toxicity to soil flora and fauna.

Graphene, electrospun membranes and granular activated carbon for eliminating heavy metals, pesticides and bacteria in water and wastewater treatment processes

The availability of safe water has a significant impact on all parts of society, its growth and sustainability, both politically and socioeconomically.

Mixing of Shiga toxin-producing and enteropathogenic Escherichia coli in a wastewater treatment plant receiving city and slaughterhouse wastewater

Wastewater of human and animal may contain Shiga toxin-producing (STEC) and enteropathogenic (EPEC) Escherichia coli. We evaluated the prevalence of such strains in a wastewater treatment plant (WWTP) receiving both city and slaughterhouse wastewater. PCR screenings were performed on 12,248 E. coli isolates. The prevalence of STEC in city wastewater, slaughterhouse wastewater and treated effluent was 0.22%, 0.07% and 0.22%, respectively. The prevalence of EPEC at the same sampling sites was 0.63%, 0.90% and 0.55%. No significant difference was observed between the sampling points. Treatment had no impact on these prevalences. Enterohemorrhagic E. coli (EHEC) O157:H7 and O111:H8 were isolated from the treated effluent rejected into the river. The characteristics of STEC and EPEC differed according to their origin. City wastewater contained STEC with various stx subtypes associated with serious human disease, whereas slaughterhouse wastewater contained exclusively STEC with stx_2e subtype. All the EPEC strains were classified as atypical and were screened for the ε, γ1 and β1 subtypes, known to be associated with the EHEC mainly involved in human infections in France. In city wastewater, eae subtypes remained largely unidentified; whereas eae-β1 was the most frequent subtype in slaughterhouse wastewater. Moreover, the EPEC isolated from slaughterhouse wastewater were positive for other EHEC-associated virulence markers, including top five serotypes, the ehxA gene, putative adherence genes and OI-122 associated genes. The possibility that city wastewater could contain a pool of stx genes associated with human disease and that slaughterhouse wastewater could contain a pool of EPEC sharing similar virulence genes with EHEC, was highlighted. Mixing of such strains in WWTP could lead to the emergence of EHEC by horizontal gene transfer.

Elucidating selection processes for antibiotic resistance in sewage treatment plants using metagenomics

Sewage treatment plants (STPs) have repeatedly been suggested as "hotspots" for the emergence and dissemination of antibiotic-resistant bacteria. A critical question still unanswered is if selection pressures within STPs, caused by residual antibiotics or other co-selective agents, are sufficient to specifically promote resistance. To address this, we employed shotgun metagenomic sequencing of samples from different steps of the treatment process in three Swedish STPs. In parallel, concentrations of selected antibiotics, biocides and metals were analyzed. We found that concentrations of tetracycline and ciprofloxacin in the influent were above predicted concentrations for resistance selection, however, there was no consistent enrichment of resistance genes to any particular class of antibiotics in the STPs, neither for biocide and metal resistance genes. The most substantial change of the bacterial communities compared to human feces occurred already in the sewage pipes, manifested by a strong shift from obligate to facultative anaerobes. Through the treatment process, resistance genes against antibiotics, biocides and metals were not reduced to the same extent as fecal bacteria. The OXA-48 gene was consistently enriched in surplus and digested sludge. We find this worrying as OXA-48, still rare in Swedish clinical isolates, provides resistance to carbapenems, one of our most critically important classes of antibiotics. Taken together, metagenomics analyses did not provide clear support for specific antibiotic resistance selection. However, stronger selective forces affecting gross taxonomic composition, and with that resistance gene abundances, limit interpretability. Comprehensive analyses of resistant/non-resistant strains within relevant species are therefore warranted.

What happens in hospitals does not stay in hospitals: antibiotic-resistant bacteria in hospital wastewater systems

Hospitals are hotspots for antimicrobial-resistant bacteria (ARB) and play a major role in both their emergence and spread. Large numbers of these ARB will be ejected from hospitals via wastewater systems. In this review, we present quantitative and qualitative data of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli, vancomycin-resistant enterococci and Pseudomonas aeruginosa in hospital wastewaters compared to community wastewaters. We also discuss the fate of these ARB in wastewater treatment plants and in the downstream environment. Published studies have shown that hospital effluents contain ARB, the burden of these bacteria being dependent on their local prevalence. The large amounts of antimicrobials rejected in wastewater exert a continuous selective pressure. Only a few countries recommend the primary treatment of hospital effluents before their discharge into the main wastewater flow for treatment in municipal wastewater treatment plants. Despite the lack of conclusive data, some studies suggest that treatment could favour the ARB, notably ESBL-producing E. coli. Moreover, treatment plants are described as hotspots for the transfer of antibiotic resistance genes between bacterial species. Consequently, large amounts of ARB are released in the environment, but it is unclear whether this release contributes to the global epidemiology of these pathogens. It is reasonable, nevertheless, to postulate that it plays a role in the worldwide progression of antibiotic resistance. Antimicrobial resistance should now be seen as an 'environmental pollutant', and new wastewater treatment processes must be assessed for their capability in eliminating ARB, especially from hospital effluents.

Identification and antimicrobial resistance prevalence of pathogenic Escherichia coli strains from treated wastewater effluents in Eastern Cape, South Africa

Antimicrobial resistance (AMR) is a global problem impeding the effective prevention/treatment of an ever-growing array of infections caused by pathogens; a huge challenge threatening the achievements of modern medicine. In this paper, we report the occurrence of multidrug resistance (MDR) in Escherichia coli strains isolated from discharged final effluents of two wastewater treatment facilities in the Eastern Cape Province of South Africa. Standard disk diffusion method was employed to determine the antibiotic susceptibility profile of 223 polymerase chain reaction (PCR)-confirmed E. coli isolates against 17 common antibiotics in human therapy and veterinary medicine. Seven virulence associated and fourteen antibiotic resistance genes were also evaluated by molecular methods. Molecular characterization revealed five pathotypes of E. coli in the following proportions: enterotoxigenic ETEC (1.4%), enteropathogenic EPEC (7.6%), enteroaggregative EAEC (7.6%), neonatal meningitis (NMEC) (14.8%), uropathogenic (41.7%), and others (26.9%). Isolates showed varying (1.7-70.6%) degrees of resistance to 15 of the test antibiotics. Multidrug resistance was exhibited by 32.7% of the isolates, with the commonest multiple antibiotic-resistant phenotype (MARP) being AP-T-CFX (12 isolates), while multiple antibiotic-resistant indices (MARI) estimated are 0.23 (Site 1) and 0.24 (Site 2). Associated antibiotic resistance genes detected in the isolates include: strA (88.2%), aadA (52.9%), cat I (15%), cmlA1 (4.6%), blaTEM (56.4%), tetA (30.4%), tetB (28.4%), tetC (42.2%), tetD (50%), tetK (11.8%), and tetM (68.6%). We conclude that municipal wastewater effluents are important reservoirs for the dissemination of potentially pathogenic E. coli (and possibly other pathogens) and antibiotic resistance genes in the aquatic milieu of the Eastern Cape and a risk to public health.

Potential pathogens, antimicrobial patterns and genotypic diversity of Escherichia coli isolates in constructed wetlands treating swine wastewater

Escherichia coli populations originating from swine houses through constructed wetlands were analyzed for potential pathogens, antimicrobial susceptibility patterns, and genotypic diversity. Escherichia coli isolates (n = 493) were screened for the presence of the following virulence genes: stx1, stx2 and eae (Shiga toxin-producing E. coli [STEC]), heat-labile enterotoxin (LT) genes and heat stable toxin STa and STb (enterotoxigenic E. coli (ETEC), cytotoxin necrotizing factors 1 and 2 (cnf1 and cnf2 [necrotoxigenic E. coli- NTEC]), as well as O and H antigens, and the presence of the antibiotic resistance genes blaTEM, blaSHV, blaCMY-2, tet A, tet B, tet C, mph(A), aadA, StrA/B, sul1, sul2 and sul3. The commensal strains were further screened for 16 antimicrobials and characterized by BOX AIR-1 PCR for unique genotypes. The highest antibiotic resistance prevalence was for tetracycline, followed by erythromycin, ampicillin, streptomycin, sulfisoxazole and kanamycin. Our data showed that most of the isolates had high distribution of single or multidrug-resistant (MDR) genotypes. Therefore, the occurrence of MDR E. coli in the wetland is a matter of great concern due to possible transfer of resistance genes from nonpathogenic to pathogenic strains or vice versa in the environment.

Prevalence and proliferation of antibiotic resistance genes in two municipal wastewater treatment plants

The propagation of antibiotic resistance genes (ARGs) is an emerging health concern worldwide. Thus, it is important to understand and mitigate their occurrence in different systems. In this study, 30 ARGs that confer resistance to tetracyclines, sulfonamides, quinolones or macrolides were detected in two activated sludge wastewater treatment plants (WWTPs) in northern China. Bacteria harboring ARGs persisted through all treatment units, and survived disinfection by chlorination in greater percentages than total Bacteria (assessed by 16S rRNA genes). Although the absolute abundances of ARGs were reduced from the raw influent to the effluent by 89.0%-99.8%, considerable ARG levels [(1.0 ± 0.2) × 10(3) to (9.5 ± 1.8) × 10(5) copies/mL)] were found in WWTP effluent samples. ARGs were concentrated in the waste sludge (through settling of bacteria and sludge dewatering) at (1.5 ± 2.3) × 10(9) to (2.2 ± 2.8) × 10(11) copies/g dry weight. Twelve ARGs (tetA, tetB, tetE, tetG, tetH, tetS, tetT, tetX, sul1, sul2, qnrB, ermC) were discharged through the dewatered sludge and plant effluent at higher rates than influent values, indicating overall proliferation of resistant bacteria. Significant antibiotic concentrations (2%-50% of raw influent concentrations) remained throughout all treatment units. This apparently contributed selective pressure for ARG replication since the relative abundance of resistant bacteria (assessed by ARG/16S rRNA gene ratios) was significantly correlated to the corresponding effluent antibiotic concentrations. Similarly, the concentrations of various heavy metals (which induce a similar bacterial resistance mechanism as antibiotics - efflux pumps) were also correlated to the enrichment of some ARGs. Thus, curtailing the release of antibiotics and heavy metals to sewage systems (or enhancing their removal in pre-treatment units) may alleviate their selective pressure and mitigate ARG proliferation in WWTPs.

Characterization of Pathogenic Escherichia coli in River Water by Simultaneous Detection and Sequencing of 14 Virulence Genes

The occurrence of pathogenic Escherichia coli in environmental waters increases the risk of waterborne disease. In this study, 14 virulence genes in 669 E. coli isolates (549 isolates from the Yamato River in Japan, and 30 isolates from each of the following hosts: humans, cows, pigs, and chickens) were simultaneously quantified by multiplex PCR and dual index sequencing to determine the prevalence of potentially pathogenic E. coli. Among the 549 environmental isolates, 64 (12%) were classified as extraintestinal pathogenic E. coli (ExPEC) while eight (1.5%) were classified as intestinal pathogenic E. coli (InPEC). Only ExPEC-associated genes were detected in human isolates and pig isolates, and 11 (37%) and five (17%) isolates were classified as ExPEC, respectively. A high proportion (63%) of cow isolates possessed Shiga-toxin genes (stx1 or stx2) and they were classified as Shiga toxin-producing E. coli (STEC) or enterohemorrhagic E. coli (EHEC). Among the chicken isolates, 14 (47%) possessed iutA, which is an ExPEC-associated gene. This method can determine the sequences as well as the presence/absence of virulence genes. By comparing the sequences of virulence genes, we determined that sequences of iutA were different among sources and may be useful for discriminating isolates, although further studies including larger numbers of isolates are needed. Results indicate that humans are a likely source of ExPEC strains in the river.

Impact of UV and peracetic acid disinfection on the prevalence of virulence and antimicrobial resistance genes in uropathogenic Escherichia coli in wastewater effluents

Wastewater discharges may increase the populations of pathogens, including Escherichia coli, and of antimicrobial-resistant strains in receiving waters. This study investigated the impact of UV and peracetic acid (PAA) disinfection on the prevalence of virulence and antimicrobial resistance genes in uropathogenic Escherichia coli (UPEC), the most abundant E. coli pathotype in municipal wastewaters. Laboratory disinfection experiments were conducted on wastewater treated by physicochemical, activated sludge, or biofiltration processes; 1,766 E. coli isolates were obtained for the evaluation. The target disinfection level was 200 CFU/100 ml, resulting in UV and PAA doses of 7 to 30 mJ/cm(2) and 0.9 to 2.0 mg/liter, respectively. The proportions of UPECs were reduced in all samples after disinfection, with an average reduction by UV of 55% (range, 22% to 80%) and by PAA of 52% (range, 11% to 100%). Analysis of urovirulence genes revealed that the decline in the UPEC populations was not associated with any particular virulence factor. A positive association was found between the occurrence of urovirulence and antimicrobial resistance genes (ARGs). However, the changes in the prevalence of ARGs in potential UPECs were different following disinfection, i.e., UV appears to have had no effect, while PAA significantly reduced the ARG levels. Thus, this study showed that both UV and PAA disinfections reduced the proportion of UPECs and that PAA disinfection also reduced the proportion of antimicrobial resistance gene-carrying UPEC pathotypes in municipal wastewaters.

Impact of wastewater treatment processes on antimicrobial resistance genes and their co-occurrence with virulence genes in Escherichia coli

An increase in the frequency of antimicrobial resistance genes (ARGs) in bacteria including Escherichia coli could be a threat to public health. This study investigated the impact of activated sludge and physicochemical wastewater treatment processes on the prevalence of ARGs in E. coli isolates. In total, 719 E. coli were isolated from the influent and effluent (prior to disinfection) of two activated sludge and two physicochemical municipal treatment plants, and genotyped using DNA microarrays. Changes in the abundance of ARGs in the E. coli population were different for the two treatment processes. Activated sludge treatment did not change the prevalence of ARG-possessing E. coli but increased the abundance of ARGs in the E. coli genome while physicochemical treatment reduced both the prevalence of ARG-carrying E. coli as well as the frequency of ARGs in the E. coli genome. Most E. coli isolates from the four treatment plants possessed ARGs of multiple antimicrobial classes, mainly aminoglycoside, β-lactams, quinolone and tetracyclines. In addition these isolates harboured DNA insertion sequence elements including integrase and transposase. A significant positive association was found between the occurrence of ARGs and virulence genotypes.

Survival of Escherichia coli in two sewage treatment plants using UV irradiation and chlorination for disinfection

We investigated the survival of Escherichia coli in two STPs utilising UV irradiation (STP-A) or chlorination (STP-B) for disinfection. In all, 370 E. coli strains isolated from raw influent sewage (IS), secondary treated effluent (STE) and effluent after the disinfection processes of both STPs were typed using a high resolution biochemical fingerprinting method and were grouped into common (C-) and single (S-) biochemical phenotypes (BPTs). In STP-A, 83 BPTs comprising 123 isolates were found in IS and STE, of which 7 BPTs survived UV irradiation. Isolates tested from the same sites of STP-B (n = 220) comprised 122 BPTs, however, only two BPTs were found post-chlorination. A representative isolate from each BPT from both STPs was tested for the presence of 11 virulence genes (VGs) associated with uropathogenic (UPEC) or intestinal pathogenic (IPEC) E. coli strains. Strains surviving UV irradiation were distributed among seven phylogenetic groups with five BPTs carrying VGs associated with either UPEC (4 BPTs) or IPEC (1 BPT). In contrast, E. coli strains found in STP-B carried no VGs. Strains from both STPs were resistant to up to 12 out of the 21 antibiotics tested but there was no significant difference between the numbers of antibiotics to which surviving strains were resistant to in these STPs. Our data suggests that some E. coli strains have a better ability to survive STPs utilising chlorination and UV irradiation for disinfection. However, strains that survive UV irradiation are more diverse and may carry more VGs than those surviving SPTs using chlorination.