Distribution of bound-PAH residues and their correlations with the bacterial community at different depths of soil from an abandoned chemical plant site

The situ pollutant residue and microbial characteristics in contaminated environments are crucial for ecological restoration and soil utilization. This work reported the variation of polycyclic aromatic hydrocarbon (PAH) residues and the bacterial community at different depths in an aged-abandoned site. These results unveiled that over 90% of low molecular weight (LMW) and medium molecular weight (MMW), 52.84-76.88% of high molecular weight (HMW) bound-PAH (BP) residues were sequestrated in humin (HM). The stresses of PAH and soil depth enhanced the frequency of bacteria associations, especially positive associations. We enriched and cultured PAH degradation bacteria (PDB) from the sampling site mainly consisting of Pseudomonas and Acinetobacter, which were originally 0.39-0.52% abundant in the sampling site. The abundances of PDB and PAH-degradation genes (PDGs) were higher at shallower depths and increased with high PAH concentration. Simultaneously, Pearson correlation analysis and experimental verification found that the process of PAH binding with SOM limited the further increase of PDB and PDGs in PAH-contaminated sites. These findings may illustrate possible ecological risks of contaminated soils and provide guidance for the isolation and application of PDB.

Antibiotic ecotoxicity and resistance risks in resource-constrained chicken and pig farming environments

Antimicrobial resistance (AMR) data from agroecosystems in low- and middle-income countries is limited. We surveyed chicken (n = 52) and pig (n = 47) farms in Kenya to understand AMR in animal-environment pathways. Using LC-MS/MS, we validated the methods for analyzing eight common antibiotics and quantified the associated risks. Chicken compost (25.8%, n = 97/376) had the highest antibiotics prevalence, followed by pig manure-fertilized soils (23.1%, n = 83/360). The average antibiotic concentration was 63.4 µg/kg, which is below the environmentally relevant threshold (100 µg/kg), except for trimethoprim (221.4 µg/kg) among antibiotics and pig manure-fertilized soils (129.3 µg/kg) across sample types. Similarly, the average AMR risk quotient (RQ) was low (RQ < 0.1), except for trimethoprim and sulfamethoxazole (RQ ≥ 1). Ecotoxicity and AMR risks increased with flock size and the number of antibiotics used by pigs. Continuous environmental monitoring and large-scale studies on antibiotic contamination are crucial for evidence-based pollution control and the effective mitigation of environmental AMR.

Antibiotic quality and use practices amongst dairy farmers and drug retailers in central Kenyan highlands

Understanding antibiotic use in dairy systems is critical to guide antimicrobial stewardship programs. We investigated antibiotic use practices in small-holder dairy farms, antibiotic quality, and antimicrobial resistance (AMR) awareness among veterinary drug retailers in a mixed farming community in the central Kenyan highlands. Data were collected from 248 dairy farms and 72 veterinary drug stores between February 2020 and October 2021. A scale was developed to measure knowledge about AMR and antibiotic use using item response theory, and regression models were used to evaluate factors associated with antibiotic use and AMR knowledge. The active pharmaceutical ingredient (API) content of 27 antibiotic samples was determined using high-performance liquid chromatography (HPLC). The presence and levels of 11 antibiotic residues in 108 milk samples collected from the study farms were also investigated using liquid chromatography tandem mass spectrometry (LC-MS/MS). Almost all farms (98.8%, n = 244) reported using antibiotics at least once in the last year, mostly for therapeutic reasons (35.5%). The most used antibiotics were tetracycline (30.6%), penicillin (16.7%), and sulfonamide (9.4%), either individually or in combination, and predominantly in the injectable form. Larger farm size (OR = 1.02, p < 0.001) and history of vaccination use (OR = 1.17, p < 0.001) were significantly associated with a higher frequency of antibiotic use. Drug retailers who advised on animal treatments had a significantly higher mean knowledge scores than those who only sold drugs. We found that 44.4% (12/27) of the tested antibiotics did not meet the United States Pharmacopeial test specifications (percentage of label claim). We detected nine antibiotics in milk, including oxytetracycline, sulfamethoxazole, and trimethoprim. However, only three samples exceeded the maximum residue limits set by the Codex Alimentarius Commission. Our findings indicate that antibiotics of poor quality are accessible and used in small-holder dairy systems, which can be found in milk. These results will aid future investigations on how to promote sustainable antibiotic use practices in dairy systems.

Tetracyclines uptake from irrigation water by vegetables: Accumulation and antimicrobial resistance risks

Wastewater irrigation may introduce antibiotic residues in the soil-plant systems. This study aimed to investigate the uptake of tetracyclines by spinach and collard greens and assess associated ecological and human health risks. Synthetic wastewater spiked with 1 ppm and 10 ppm of oxytetracycline, doxycycline, and tetracycline was used to grow vegetables in a greenhouse pot experiment. The uptake and accumulation of the tetracyclines were low and residual concentrations in the soil were negligible. All the tetracyclines were detected at concentrations ranging from 1.68 to 51.41 μg/g (spinach) and 1.94-30.95 μg/g (collard greens). The accumulation rate was in a dose-response scenario with a bioconcentration factor of 6.34 mL/kg (spinach) and 2.64 mL/kg (collard greens). Oxytetracycline had the highest accumulation in leaves, followed by doxycycline and tetracycline, and the residual concentrations followed the same order. The highest residual concentration was in soils receiving 10 ppm oxytetracycline. Residual concentrations in the soil were lower than accumulated levels and exerted negligible ecological risks. Tetracyclines accumulation in spinach significantly differed between the vegetables demonstrating a subspecies difference in uptake and accumulation. Ecological risk quotient (RQ) and human health risk quotient (HQ) were below thresholds that would exert toxicity and resistance selection impacts. Although RQs and HQs are low (<0.1), this study shows that the vegetables accumulate tetracyclines from irrigation water, posing plausible human health risks to allergic individuals. Similarly, the ecological risks cannot be ignored because the synergistic and antagonistic effects of sublethal concentrations can perturb ecosystem processes.

Intersections between climate change and antimicrobial resistance: a systematic scoping review

Climate change and antimicrobial resistance (AMR) present crucial challenges for the health and wellbeing of people, animals, plants, and ecosystems worldwide, yet the two are largely treated as separate and unrelated challenges. The aim of this systematic scoping Review is to understand the nature of the growing evidence base linking AMR and climate change and to identify knowledge gaps and areas for further research. We conducted a systematic search of the peer-reviewed literature in Scopus, Web of Science, and PubMed on 27 June, 2022. Our search strategy identified and screened 1687 unique results. Data were extracted and analysed from 574 records meeting our inclusion criteria. 222 (39%) of these reviewed articles discussed harmful synergies in which both climate change and AMR exist independently and can interact synergistically, resulting in negative outcomes. Just over a quarter (n=163; 28%) of the literature contained general or broad references to AMR and climate change, whereas a fifth (n=111; 19%) of articles referred to climate change influencing the emergence and evolution of AMR. 12% of articles (n=70) presented positive synergies between approaches aimed at addressing climate change and interventions targeting the management and control of AMR. The remaining literature focused on the shared drivers of AMR and climate change, the trade-offs between climate actions that have unanticipated negative outcomes for AMR (or vice versa), and, finally, the pathways through which AMR can negatively influence climate change. Our findings indicate multiple intersections through which climate change and AMR can and do connect. Research in this area is still nascent, disciplinarily isolated, and only beginning to converge, with few documents primarily focused on the equal intersection of both topics. Greater empirical and evidence-based attention is needed to investigate knowledge gaps related to specific climate change hazards and antimicrobial resistant fungi, helminths, protists, and viruses.