Effect of Powdered Activated Carbon as Advanced Step in Wastewater Treatments on Antibiotic Resistant Microorganisms

Mapping antimicrobial resistance landscape at a city scale sewage network

Wastewater is a valuable source for monitoring contaminants of biotic or abiotic origin. Antimicrobial resistance (AMR) has emerged as a public health threat that consists of the ability of microorganisms to resist the effects of antimicrobial compounds, rendering them very difficult or impossible to eradicate in case of infection. Considering the dissemination of antimicrobial resistance genes (ARGs) to a wide number of ecosystems, there is a need for the identification of hotspots that concentrate antimicrobial resistance determinants. A comprehensive investigation conducted at a city-scale in Sabadell (Barcelona, Spain) has integrated both phenotypic and genotypic methodologies, including metagenomics and culture-based techniques coupled with whole-genome sequencing (WGS), to monitor ARG presence in seven different spots of the sewage system. Metagenomics approach identified 262 ARG variants across analyzed sampling sites, grouped into 15 resistance categories. The most prevalent ARGs were macrolides-lincosamides-class B streptogramins (MLSB) (35.1 %) and beta-lactams (28.7 %), including carbapenems (5.9 %) and cephalosporins (5.3 %). MLSB resistance featured dominant msr(E) and mph(E) genes, the most abundant ARGs in our study. ARGs conferring resistance to beta-lactam were dominated by blaOXA-464, blaOXA-491, and blaNPS. Key genes for carbapenem (blaOXA-372, blaKPC-2) and cephalosporin (blaOXA-10, blaOXA-1) resistance were identified. The hospital sector exhibited the highest relative abundance of ARGs, dominated by beta-lactams, MLSB, and aminoglycosides. Wastewater treatment plant (WWTP) entrance points and residential areas displayed similar ARG profiles, while WWTP effluent and industrial zones had the lowest ARG levels. WWTP significantly reduced ARG presence (93.3 %). The characterization of antibiotic-resistant bacterial isolates found that most abundant ARGs were predominantly plasmid-borne, favoring ARG spread across bacterial genera. This finding confirmed the significant role of plasmids in ARG dissemination, increasing both diversity and prevalence within waterborne bacterial communities. City-scale surveillance programs can play a pivotal role in guiding effective measures to reduce the dissemination of AMR and mitigate their environmental impact.

An evaluation of conventional and nature-based technologies for controlling antibiotic-resistant bacteria and antibiotic-resistant genes in wastewater treatment plants

Antibiotic resistance is a globally recognized health concern which leads to longer hospital stays, increased morbidity, increased mortality, and higher medical costs. Understanding how antibiotic resistance persists and exchanges in environmental systems like soil, water, and wastewater are critically important for understanding the emergence of pathogens with new resistance profiles and the subsequent exposure of people who indirectly/directly come in contact with these pathogens. There are concerns about the widespread application of prophylactic antibiotics in the clinical and agriculture sectors, as well as chemicals/detergents used in food and manufacturing industries, especially the quaternary ammonium compounds which have been found responsible for the generation of resistant genes in water and soil. The rates of horizontal gene transfer increase where there is a lack of proper water/wastewater infrastructure, high antibiotic manufacturing industries, or endpoint users - such as hospitals and intensive agriculture. Conventional wastewater treatment technologies are often inefficient in the reduction of ARB/ARGs and provide the perfect combination of conditions for the development of antibiotic resistance. The wastewater discharged from municipal facilities may therefore be enriched with bacterial communities/pathogens and provide a suitable environment (due to the presence of nutrients and other pollutants) to enhance the transfer of antibiotic resistance. However, facilities with tertiary treatment (either traditional/emerging technologies) provide higher rates of reduction. This review provides a synthesis of the current understanding of wastewater treatment and antibiotic resistance, examining the drivers that may accelerate their possible transmission to a different environment, and highlighting the need for tertiary technologies used in treatment plants for the reduction of resistant bacteria/genes.

Modern knowledge-scape possess petite influence on the factual persistence of resistance determinants (ARGs/MGEs): A map and assessment of discharged wastewater and water bodies

Antibiotic resistance genes (ARGs) and Mobile genetic elements (MGEs) are major global emerging pollutants of the environment and water nexus which various investigators of related studies have reported. Observing ARGs and MGEs in water bodies, wastewater treatment systems, and estuaries is indicative of relevant risk, resistant bacteria/ARGs spread or potential health concern and may result environmental pathogen bloom if appropriate research-based strategies are not implemented to remove these lethal genetic materials. Despite reports and knowledge-based strategies for removal, the challenge yet persists. This study aims to appraise the impact/contribution of related studies and emphasize the necessity for applying combined research-based/practitioners approach in addressing the expanding challenge of ARGs/MGEs in wastewater/waterbodies. The study describes a bibliometric assessment of antibiotic resistance determinants annual scientific publications on the Web of Science, an annual growth rate of related articles, top articles per citations with search topics and content-review analysis to evaluate the methods of removal of ARGs/MGEs. A total of 1301 articles of wastewater treatment systems were retrieved with date range of 1997-2019. A description of the study Annual Growth Rate of 37.82% at R² of 0.7863 was observed with an increasing article publication and a decreasing total citation rate indicating persistent reports of dispersion on ARGs/MGEs studies in the water bodies and environment. Although there abound extensive studies and reports of ARGs and MGEs in water nexus and wastewater release with research based removal strategies, the impact of such reports have not been fully actualized amongst wastewater system practitioners. A lucid drive towards implementing ARGs/MGEs removal strategies from the environment by applying affirmed research-based methods are suggestive.

Advanced wastewater treatment with ozonation and granular activated carbon filtration: Inactivation of antibiotic resistance targets in a long-term pilot study

The inactivation of antibiotic resistant bacteria (ARB) and genes (ARGs) in an advanced plant combining ozonation and granular activated carbon (GAC) filtration applied for effluent after conventional activated sludge treatment at a full-scale urban wastewater treatment plant was investigated for over 13 consecutive months. The nitrite compensated specific ozone dose ranged between 0.4 and 0.7 g O₃/g DOC with short-time sampling campaigns (0.2-0.9 g O₃/g DOC). Samples were analysed with culture-dependent methods for bacterial targets and with qPCR for genes. The log removal values were correlated with a decrease of the matrix UV absorption at 254 nm (ΔUV₂₅₄) and indicated a range of ΔUV₂₅₄ that corresponds to a sufficient membrane damage to affect DNA. For trimethoprim/sulfamethoxazole resistant E. coli, sul1, ermB and tetW, this phase was observed at ΔUV₂₅₄ of ~30 % (~0.5 g O₃/g DOC). For ampicillin resistant E. coli and bla_TEM-1, it was observed around 35-40 % (~0.7 g O₃/g DOC), which can be linked to mechanisms related to oxidative damages in bacteria resistant to bactericidal antibiotics. GAC treatment resulted in a further abatement for trimethoprim/sulfamethoxazole E. coli, sul1 and tetW, and in increase in absolute and relative abundance of ermB and bla_TEM-1.

Metagenomic analysis of microbiota and antibiotic resistome in household activated carbon drinking water purifiers

Existing drinking water treatment systems have limited ability to control emerging contaminants such as antibiotic resistance genes (ARGs). Household activated carbon water purifiers (HWPs) are convenient measures to assure drinking water quality. However, ARGs distribution in HWPs has not been reported. Here, ARGs, mobile genetic elements (MGEs) and bacteria communities were profiled in tap water (TW), filter water (FW) and activated carbon (AC) biofilm from six kinds of HWPs after 80 days operation, using metagenomics. Results showed that the bacteria community diversities in FW and AC were higher than those in TW. A total of 88, 116 and 80 ARG subtypes were detected in TW, AC and FW, respectively. The AC structure was an important factor influencing the bacterial communities and ARG profiles in FW. The network analysis revealed the co-occurrence patterns between ARGs and bacteria. SourceTracker analyses showed AC biofilms were important contributors of microbes (29-79%) and ARGs (17-53%) in FW. Moreover, MGEs e.g. pBBta01, pMKMS02 and pMFLV01 plasmids, and ISMysp3 had significant co-occurrence patterns with ARGs in the AC biofilms. This study helps to understand the actual purification effect of HWPs and provides a theoretical reference for the management and control of ARGs pollution in domestic drinking water.

Fate of antibiotics and antibiotic resistance genes during conventional and additional treatment technologies in wastewater treatment plants

Information on the removal of antibiotics and ARGs in full-scale WWTPs (with or without additional treatment technology) is limited. However, it is important to understand the efficiency of full-scale treatment technologies in removing antibiotics and ARGs under a variety of conditions relevant for practice to reduce their environmental spreading. Therefore, this study was performed to evaluate the removal of antibiotics and ARGs in a conventional wastewater treatment plant (WWTP A) and two full-scale combined with additional treatment technologies. WWTP B, a conventional activated sludge treatment followed by an activated carbon filtration step (1-STEP® filter) as a final treatment step. WWTP C, a treatment plant using aerobic granular sludge (NEREDA®) as an alternative to activated sludge treatment. Water and sludge were collected and analysed for 52 antibiotics from four target antibiotic groups (macrolides, sulfonamides, quinolones, tetracyclines) and four target ARGs (ermB, sul 1, sul 2 and tetW) and integrase gene class 1 (intI1). Despite the high removal percentages (79-88%) of the total load of antibiotics in all WWTPs, some antibiotics were detected in the various effluents. Additional treatment technology (WWTP C) showed antibiotics removal up to 99% (tetracyclines). For ARGs, WWTP C reduced 2.3 log followed by WWTP A with 2.0 log, and WWTP B with 1.3 log. This shows that full-scale WWTP with an additional treatment technology are promising solutions for reducing emissions of antibiotics and ARGs from wastewater treatment plants. However, total removal of the antibiotics and ARGS cannot be achieved for all types of antibiotics and ARGs. In addition, the ARGs were more abundant in the sludge compared to the wastewater effluent suggesting that sludge is an important reservoir representing a source for later ARG emissions upon reuse, i.e. as fertilizer in agriculture or as resource for bioplastics or bioflocculants. These aspects require further research.

Charcoal-based mouthwashes: a literature review

The commercial marketplace has seen a rapid increase in the number of over-the-counter charcoal-containing mouthwashes. The purpose of this systemic review was to examine the clinical and laboratory evidence supporting therapeutic claims of efficacy and safety of use of charcoal-based mouthwashes. Secondly, the product labels and information of 36 commercially marketed charcoal mouthwashes were reviewed for active ingredients. Only 8% of charcoal mouthwashes contained an active ingredient, such as cetylpyridinium chloride or chlorhexidine. There is insufficient evidence to substantiate the therapeutic and cosmetic marketing claims of charcoal-based mouthwashes, including antimicrobial activity, anti-halitosis, tooth whitening, periodontal disease control, caries reduction and tooth remineralisation, among others. Moreover, there is no available information on charcoal particulate size or abrasivity of any of these products. Dental clinicians should advise their patients to exercise caution when using over-the-counter charcoal-containing mouthwashes because of the lack of evidence supporting therapeutic or cosmetic effectiveness as well as safety.