Needles in haystacks: monitoring the potential escape of bioaerosolised antibacterial resistance genes from wastewater treatment plants with air and phyllosphere sampling

Wastewater treatment plants are well-known point sources of emissions of antibacterial resistance genes (ARGs) into the environment. Although most work to date has focused on ARG dispersal via effluent, aerial dispersal in bioaerosols is a poorly understood, but likely important vector for ARG dispersal. Recent evidence suggests that ARG profiles of the conifer needle phyllosphere could be used to measure bioaerosol dispersal from anthropogenic sources. Here, we assessed airborne dispersal of ARGs from wastewater treatment plants in Wales, UK and Quebec, Canada, using conifer needles as passive bioaerosol monitors. ARG profiles of wastewater were compared to those of conifer phyllosphere using high-throughput qPCR. ARG richness was significantly lower in conifer phyllosphere samples than wastewater samples, though no differences were observed across the dispersal gradients. Mean copy number of ARGs followed a similar trend. ARG profiles showed limited, but consistent patterns with increasing distance from wastewater treatment plants, but these did not align with those of wastewater samples. For example, proportional abundance of aminoglycosides decreased over the dispersal gradient in Wales, whereas mobile genetic elements showed the inverse relationship. In summary, while distinct ARG profiles exist along dispersal gradients, links to those of wastewater were not apparent.

[Microplastic-Induced Alterations to Antibiotic Resistance Genes in Seawater]

The increasing and combined pollution of microplastics (MPs) and antibiotic resistance genes (ARGs) in aquatic environments is a great ecological and health concern. However, MP-induced alterations to ARGs in seawater is poorly understood, impeding risk assessment of plastics. We profiled the diversity and abundance of ARGs and mobile genetic elements (MGEs) in seawater after the addition of three different MPs (PE, PVC, and PVA) and 49-day aerated incubation.A total of 20, 35, 42, and 64 ARGs were detected in BLK, PE, PVC, and PVA, with 2, 4, 2, and 3 MGEs, respectively. The absolute abundance of ARGs in the seawater aerated with MPs ranged from 4.01×10⁶ copies ·L^-1 to 1.05×10⁸ copies ·L^-1. Additionally, the variety and richness of ARGs and MGEs in PVA were significantly higher than in the original seawater, or the seawater aerated with the other two MPs. This indicates that PVA, which is water soluble, could induce more diverse and abundant ARGs in seawater. Significant correlations among ARGs, MGEs, and 16S rRNA genes were observed, implying that the occurrence of MGEs in seawater may accelerate the transmission of ARGs through horizontal gene transfer, and bacterial microorganisms could directly affect the propagation and dissemination of ARGs.

Developing Surrogate Markers for Predicting Antibiotic Resistance "Hot Spots" in Rivers Where Limited Data Are Available

Pinpointing environmental antibiotic resistance (AR) hot spots in low-and middle-income countries (LMICs) is hindered by a lack of available and comparable AR monitoring data relevant to such settings. Addressing this problem, we performed a comprehensive spatial and seasonal assessment of water quality and AR conditions in a Malaysian river catchment to identify potential "simple" surrogates that mirror elevated AR. We screened for resistant coliforms, 22 antibiotics, 287 AR genes and integrons, and routine water quality parameters, covering absolute concentrations and mass loadings. To understand relationships, we introduced standardized "effect sizes" (Cohen's D) for AR monitoring to improve comparability of field studies. Overall, water quality generally declined and environmental AR levels increased as one moved down the catchment without major seasonal variations, except total antibiotic concentrations that were higher in the dry season (Cohen's D > 0.8, P < 0.05). Among simple surrogates, dissolved oxygen (DO) most strongly correlated (inversely) with total AR gene concentrations (Spearman's ρ 0.81, P < 0.05). We suspect this results from minimally treated sewage inputs, which also contain AR bacteria and genes, depleting DO in the most impacted reaches. Thus, although DO is not a measure of AR, lower DO levels reflect wastewater inputs, flagging possible AR hot spots. DO measurement is inexpensive, already monitored in many catchments, and exists in many numerical water quality models (e.g., oxygen sag curves). Therefore, we propose combining DO data and prospective modeling to guide local interventions, especially in LMIC rivers with limited data.

[Microplastics-Induced Shifts of Diversity and Abundance of Antibiotic Resistance Genes in River Water]

Microplastics (MPs) and antibiotic resistance genes (ARGs) are both considered emerging contaminants of increasing concern because their combined pollution poses a serious risk to the ecological environment and human health. In this study, high-throughput quantitative PCR techniques were used to investigate the diversity and abundance of ARGs in river water, to which two different microplastics (PVC and PVA) were added for aerated incubation. The results showed that ARGs in river water were diverse, and microplastics could induce more types of ARGs. Although the number and abundance of ARGs decreased in all three treatments, which were cultivated for 14 d by aeration, compared to those in non-treated samples, the total abundance of ARGs in treatments aerated with MPs were higher than those aerated without MPs, especially in the samples treated with water-soluble microplastics (PVA). Significant correlations between the abundance of ARGs and mobile genetic elements (MGEs) were observed, implying that the occurrence of MGEs may potentially affect the transmission and distribution of ARGs through horizontal gene transfer (HGT) in river water.

[Profiles and Risk of Antibiotic Resistance Genes in Domestic Wells in the Maozhou River Basin]

Intensive use of antibiotics promotes the occurrence and development of antibiotic resistance. Antibiotic resistance genes (ARGs) enter water environments from human and animal sources. Groundwater serves as an important water supply, while the profiles and risk of ARGs in groundwater remain unknown. The abundance and profiles of ARGs in 11 domestic wells in the Maozhou River basin of Shenzhen City were analyzed by high-throughput qPCR. The results showed that a total of 141 ARGs and 8 mobile genetic elements (MGEs) were detected, of which the genes corresponding resistance to sulfonamides, multidrugs, and aminoglycosides were the most abundant. In each well, the number of detected ARGs and MGEs ranged from 48 to 89, with an average of 68. When normalized by the abundance of 16S rRNA genes, it was found that each bacterium carried at least one ARG in the groundwater of W7, W8, and W10, while in W11, each bacterium carried at least four ARGs. Clinically relevant ARGs that code for resistance to glycopeptide (blaSHV, blaTEM, blaCTX, and blaOXA-1), β-lactams (vanB and vanC-03), or chloramphenicol (floR) were found in groundwater. In addition, the abundance of sulfonamides, multidrugs, aminoglycosides, β-lactam, and chloramphenicol resistance genes were positively correlated with the abundance of MGEs (P<0.01), suggesting that MGEs may promote the spread of ARGs in groundwater.

Preferential flow paths shape the structure of bacterial communities in a clayey till depth profile

Preferential flow paths in subsurface soils serve as transport routes for water, dissolved organic matter and oxygen. Little is known about bacterial communities in flow paths or in subsoils below ∼4 m. We compared communities from preferential flow paths (biopores, fractures and sand lenses) with those in adjacent matrix sediments of clayey till from the plough layer to a depth of 6 m. 16S rRNA gene-targeted community analysis showed bacterial communities of greater abundance and diversity in flow paths than in matrix sediments at all depths. Deep fracture communities contained a higher relative abundance of aerobes and plant material decomposers like Nitrospirae, Acidobacteria and Planctomycetes than adjacent matrix sediments. Similarly, analyses of the relative abundances of archaeal amoA, nirK and dsrB genes indicated transition from aerobic to anaerobic nitrogen and sulphur cycling at greater depth in preferential flow paths than in matrix sediments. Preferential flow paths in the top 260 cm contained more indicator operational taxonomic units from the plough layer community than the matrix sediments. This study indicates that the availability of oxygen and organic matter and downward transport of bacteria shape bacterial communities in preferential flow paths, and suggests that their lifestyles differ from those of bacteria in matrix communities.

[Effects of Microplastics on Antibiotic Resistance Genes in Estuarine Sediments]

Microplastics and antibiotic resistance genes (ARGs) are emerging pollutants/contaminants, and are also the research hotspots concerning environmental health in the past few years. To explore the effects of microplastics on ARGs in estuarine sediment, three different microplastics were added to microcosm incubation experiments of sediments. Then, we investigated the persistence, abundance, diversity, and shifts of the ARGs in estuarine sediments by high-throughput quantitative polymerase chain reaction (PCR). The results showed that the microplastics significantly changed the structure of ARGs in the sediments. PVC and PE, which are hard to degrade, had significant effects on the structures and types of ARGs. However, the PVA, which is soluble, reduced the types and persistence of ARGs significantly. The abundance of ARGs in S_PVC, S_PE, and S_PVA were 4.1×10⁹, 8.1×10⁹, and 2.0×10⁹ copies·g^-1, respectively. The abundance of ARGs in sediments with added PE almost increased by one order of magnitude, implying that microplastics could significantly increase the abundance of ARGs in sediments. Furthermore, OLS regression analysis showed that ARGs are significantly correlated with transposon and integron, suggesting that mobile genetic elements (MGEs) may promote the transfer and dissemination of ARGs.

Transcriptional Profiling of Immune-Related Genes in Leishmania infantum-Infected Mice: Identification of Potential Biomarkers of Infection and Progression of Disease

Leishmania spp. is a protozoan parasite that affects millions of people around the world. At present, there is no effective vaccine to prevent leishmaniases in humans. A major limitation in vaccine development is the lack of precise understanding of the particular immunological mechanisms that allow parasite survival in the host. The parasite-host cell interaction induces dramatic changes in transcriptome patterns in both organisms, therefore, a detailed analysis of gene expression in infected tissues will contribute to the evaluation of drug and vaccine candidates, the identification of potential biomarkers, and the understanding of the immunological pathways that lead to protection or progression of disease. In this large-scale analysis, differential expression of 112 immune-related genes has been analyzed using high-throughput qPCR in spleens of infected and naïve Balb/c mice at four different time points. This analysis revealed that early response against Leishmania infection is characterized by the upregulation of Th1 markers and M1-macrophage activation molecules such as Ifng, Stat1, Cxcl9, Cxcl10, Ccr5, Cxcr3, Xcl1, and Ccl3. This activation doesn't protect spleen from infection, since parasitic burden rises along time. This marked difference in gene expression between infected and control mice disappears during intermediate stages of infection, probably related to the strong anti-inflammatory and immunosuppresory signals that are activated early upon infection (Ctla4) or remain activated throughout the experiment (Il18bp). The overexpression of these Th1/M1 markers is restored later in the chronic phase (8 wpi), suggesting the generation of a classical "protective response" against leishmaniasis. Nonetheless, the parasitic burden rockets at this timepoint. This apparent contradiction can be explained by the generation of a regulatory immune response characterized by overexpression of Ifng, Tnfa, Il10, and downregulation Il4 that counteracts the Th1/M1 response. This large pool of data was also used to identify potential biomarkers of infection and parasitic burden in spleen, on the bases of two different regression models. Given the results, gene expression signature analysis appears as a useful tool to identify mechanisms involved in disease outcome and to establish a rational approach for the identification of potential biomarkers useful for monitoring disease progression, new therapies or vaccine development.

[Distribution Characteristics of Antibiotic Resistance Genes in Sika Deer Farm]

Sika deer breeding is rapidly developing in South China during the recent years; however, the impact of sika deer breeding on the abundance and diversity of antibiotic resistance genes (ARGs) in sika deer farm remains elusive. In this study, profiles of ARGs were investigated using high-throughput qPCR technique. The results showed that the abundance of ARGs varied among different samples in the following order, deer manure composting > deer manure > vegetable soil > pristine soil, and the profiles of ARGs in these samples were significantly different (P<0.05). The abundance of ARGs was significantly correlated to that of mobile genetic elements (MGEs), implicating the potential of horizontal transfer of ARGs, which might accelerate the dissemination and enrichment of ARGs in the environment of sika deer farm.

[Comparative Investigation of Antibotic Resistance Genes Between Wastewater and Landfill Leachate]

The increasing output of wastewater and landfill leachate during the rapid urbanization exacerbated the human health risks induced by antibiotic resistance genes(ARGs). For further insight into antibiotic resistance genes(ARGs) of wastewater (adding leachate before treatment) and landfill leachate, high-throughput qPCR technique was used to investigate their abundance and diversities. A total of 187 unique ARGs were detected in wastewater, which was significantly higher than that in leachate (39 unique ARGs were detected)(P<0.05). A total of 119 antibiotic resistance genes were significantly enriched in wastewater compared with the landfill leachate (P<0.05), especially the tnpA-04 and bla_VEB, which belongs to mobile gene elements(MGEs) and β-Lactamase, increased by 3338-fold and 1061-fold, respectively. Our results showed that the profile of ARGs was significantly different between the wastewater and leachate, and the wastewater was the important reservoir of ARGs.