Bioactivity of Eugenol: A Potential Antibiotic Adjuvant with Minimal Ecotoxicological Impact.

Combining commercial antibiotics with adjuvants to lower their minimum inhibitory concentration (MIC) is vital in combating antimicrobial resistance. Evaluating the ecotoxicity of such compounds is crucial due to environmental and health risks. Here, eugenol was assessed as an adjuvant for 7 commercial antibiotics against 14 pathogenic bacteria in vitro, also examining its acute ecotoxicity on various soil and water organisms (microbiota, Vibrio fischeri, Daphnia magna, Eisenia foetida, and Allium cepa). Using microdilution methods, checkerboard assays, and kinetic studies, the MICs for eugenol were determined together with the nature of its combinations with antibiotics against bacteria, some unexposed to eugenol previously. The lethal dose for the non-target organisms was also determined, as well as the Average Well Color Development and the Community-Level Physiological Profiling for soil and water microbiota. Our findings indicate that eugenol significantly reduces MICs by 75 to 98%, which means that it could be a potent adjuvant. Ecotoxicological assessments showed eugenol to be less harmful to water and soil microbiota compared to studied antibiotics. While Vibrio fischeri and Daphnia magna were susceptible, Allium cepa and Eisenia foetida were minimally affected. Given that only 0.1% of eugenol is excreted by humans without metabolism, its environmental risk when used with antibiotics appears minimal.

Ecotoxicity of five veterinary antibiotics on indicator organisms and water and soil communities.

This study explores the environmental effects of five common veterinary antibiotics widely detected in the environment, (chlortetracycline,CTC; oxytetracycline,OTC; florfenicol,FF; neomycin, NMC; and sulfadiazine, SDZ) on four bioindicators: Daphnia magna, Vibrio fischeri, Eisenia fetida, and Allium cepa, representing aquatic and soil environments. Additionally, microbial communities characterized through 16 S rRNA gene sequencing from a river and natural soil were exposed to the antibiotics to assess changes in population growth and metabolic profiles using Biolog EcoPlates™. Tetracyclines are harmful to Vibrio fisheri (LC50 ranges of 15-25 µg/mL), and the other three antibiotics seem to only affect D. magna, especially, SDZ. None of the antibiotics produced mortality in E. fetida at concentrations below 1000 mg/kg. NMC and CTC had the highest phytotoxicities in A. cepa (LC50 = 97-174 µg/mL, respectively). Antibiotics significantly reduced bacterial metabolism at 0.1-10 µg/mL. From the highest to the lowest toxicity on aquatic communities: OTC > FF > SDZ ≈ CTC > NMC and on edaphic communities: CTC ≈ OTC > FF > SDZ > NMC. In river communities, OTC and FF caused substantial decreases in bacterial metabolism at low concentrations (0.1 µg/mL), impacting carbohydrates, amino acids (OTC), and polymers (FF). At 10 µg/mL and above, OTC, CTC, and FF significantly decreased metabolizing all tested metabolites. In soil communities, a more pronounced decrease in metabolizing ability, detectable at 0.1 µg/mL, particularly affected amines/amides and carboxylic and ketonic acids (p < 0.05). These new ecotoxicity findings underscore that the concentrations of these antibiotics in the environment can significantly impact both aquatic and terrestrial ecosystems.

Hydroquinone Ecotoxicity: Unveiling Risks in Soil and River Ecosystems with Insights into Microbial Resilience.

Despite widespread industrial use, the environmental safety of hydroquinone (HQ), a benzene compound from plants used in processes like cosmetics, remains uncertain. This study evaluated the ecotoxicological impact of HQ on soil and river environments, utilizing non-target indicator organisms from diverse trophic levels: Daphnia magna, Aliivibrio fischeri, Allium cepa, and Eisenia fetida. For a more environmentally realistic assessment, microbial communities from a river and untreated soil underwent 16S rRNA gene sequencing, with growth and changes in community-level physiological profiling assessed using Biolog EcoPlate™ assays. The water indicator D. magna exhibited the highest sensitivity to HQ (EC50 = 0.142 µg/mL), followed by A. fischeri (EC50 = 1.446 µg/mL), and A. cepa (LC50 = 7.631 µg/mL), while E. fetida showed the highest resistance (EC50 = 234 mg/Kg). Remarkably, microbial communities mitigated HQ impact in both aquatic and terrestrial environments. River microorganisms displayed minimal inhibition, except for a significant reduction in polymer metabolism at the highest concentration (100 µg/mL). Soil communities demonstrated resilience up to 100 µg/mL, beyond which there was a significant decrease in population growth and the capacity to metabolize carbohydrates and polymers. Despite microbial mitigation, HQ remains highly toxic to various trophic levels, emphasizing the necessity for environmental regulations.

Enhancing Commercial Antibiotics with Trans-Cinnamaldehyde in Gram-Positive and Gram-Negative Bacteria: An In Vitro Approach.

One strategy to mitigate the emergence of bacterial resistance involves reducing antibiotic doses by combining them with natural products, such as trans-cinnamaldehyde (CIN). The objective of this research was to identify in vitro combinations (CIN + commercial antibiotic (ABX)) that decrease the minimum inhibitory concentration (MIC) of seven antibiotics against 14 different Gram-positive and Gram-negative pathogenic bacteria, most of them classified as ESKAPE. MIC values were measured for all compounds using the broth microdilution method. The effect of the combinations on these microorganisms was analyzed through the checkboard assay to determine the type of activity (synergy, antagonism, or addition). This analysis was complemented with a kinetic study of the synergistic combinations. Fifteen synergistic combinations were characterized for nine of the tested bacteria. CIN demonstrated effectiveness in reducing the MIC of chloramphenicol, streptomycin, amoxicillin, and erythromycin (94-98%) when tested on Serratia marcescens, Staphylococcus aureus, Pasteurella aerogenes, and Salmonella enterica, respectively. The kinetic study revealed that when the substances were tested alone at the MIC concentration observed in the synergistic combination, bacterial growth was not inhibited. However, when CIN and the ABX, for which synergy was observed, were tested simultaneously in combination at these same concentrations, the bacterial growth inhibition was complete. This demonstrates the highly potent in vitro synergistic activity of CIN when combined with commercial ABXs. This finding could be particularly beneficial in livestock farming, as this sector witnesses the highest quantities of antimicrobial usage, contributing significantly to antimicrobial resistance issues. Further research focused on this natural compound is thus warranted for this reason.

Assessing the Ecotoxicity of Eight Widely Used Antibiotics on River Microbial Communities.

Global prevalence of antibiotic residues (ABX) in rivers requires ecotoxicological impact assessment. River microbial communities serve as effective bioindicators for this purpose. We quantified the effects of eight commonly used ABXs on a freshwater river microbial community using Biolog EcoPlates™, enabling the assessment of growth and physiological profile changes. Microbial community characterization involved 16S rRNA gene sequencing. The river community structure was representative of aquatic ecosystems, with the prevalence of Cyanobacteria, Proteobacteria, Actinobacteria, and Bacteroidetes. Our findings reveal that all ABXs at 100 µg/mL reduced microbial community growth and metabolic capacity, particularly for polymers, carbohydrates, carboxylic, and ketonic acids. Chloramphenicol, erythromycin, and gentamicin exhibited the highest toxicity, with chloramphenicol notably impairing the metabolism of all studied metabolite groups. At lower concentrations (1 µg/mL), some ABXs slightly enhanced growth and the capacity to metabolize substrates, such as carbohydrates, carboxylic, and ketonic acids, and amines, except for amoxicillin, which decreased the metabolic capacity across all metabolites. We explored potential correlations between physicochemical parameters and drug mechanisms to understand drug bioavailability. Acute toxicity effects at the river-detected low concentrations (ng/L) are unlikely. However, they may disrupt microbial communities in aquatic ecosystems. The utilization of a wide array of genetically characterized microbial communities, as opposed to a single species, enables a better understanding of the impact of ABXs on complex river ecosystems.

Ecotoxicological Study of Tannic Acid on Soil and Water Non-Target Indicators and Its Impact on Fluvial and Edaphic Communities.

Tannic acid (TA) is a key tannin extensively used in the leather industry, contributing to around 90% of global leather production. This practice leads to the generation of highly polluting effluents, causing environmental harm to aquatic ecosystems. Additionally, tannins like TA degrade slowly under natural conditions. Despite efforts to reduce pollutant effluents, limited attention has been devoted to the direct environmental impact of tannins. Moreover, TA has garnered increased attention mainly due to its applications as an antibacterial agent and anti-carcinogenic compound. However, our understanding of its ecotoxicological effects remains incomplete. This study addresses this knowledge gap by assessing the ecotoxicity of TA on non-target indicator organisms in both water (Vibrio fischeri, Daphnia magna) and soil environments (Eisenia foetida, Allium cepa), as well as natural fluvial and edaphic communities, including periphyton. Our findings offer valuable insights into TA's ecotoxicological impact across various trophic levels, underscoring the need for more comprehensive investigations in complex ecosystems. Our results demonstrate that TA exhibits ecotoxicity towards specific non-target aquatic organisms, particularly V. fischeri and D. magna, and phytotoxicity on A. cepa. The severity of these effects varies, with V. fischeri being the most sensitive, followed by D. magna and A. cepa. However, the soil-dwelling invertebrate E. foetida shows resistance to the tested TA concentrations. Furthermore, our research reveals that substantial TA concentrations are required to reduce the growth of river microbial communities. Metabolic changes, particularly in amino acid and amine metabolism, are observed at lower concentrations. Notably, the photosynthetic yield of river periphyton remains unaffected, even at higher concentrations. In contrast, soil microbial communities exhibit greater sensitivity, with significant alterations in population growth and metabolic profiles at a very low concentration of 0.2 mg/L for all metabolites. In summary, this study offers valuable insights into the ecotoxicological effects of TA on both aquatic and terrestrial environments. It underscores the importance of considering a variety of non-target organisms and complex communities when assessing the environmental implications of this compound.

Antibiotic properties of Satureja montana L. hydrolate in bacteria and fungus of clinical interest and its impact in non-target environmental microorganisms.

The aim of this study was to analyse the microbicidal and microbiostatic activity of S. montana hydrolate L., the water-soluble fraction of the hydro-distillation process used to obtain the essential oil, on 14 Gram-positive and Gram-negative bacteria and a fungus of clinical interest. To consider whether this hydrolate is a more environmentally friendly alternative to traditional antibiotics, its effect on non-target microorganisms in the aquatic and terrestrial environment was analysed using natural soil and river microorganism communities, characterized through 16S rRNA gene sequencing. Results showed that S. montana hydrolate was especially effective (25% v/v concentration) against Pasteurella aerogenes, Streptococcus agalactiae and Acinetobacter baumannii (priority 1, WHO). It was also a microbicide for a further 7 bacterial strains and the fungus Candida albicans (50% v/v concentration). The river and soil communities exposed to the hydrolate showed a decrease in their growth, as well as a decrease in their ability to metabolize polymers and carbohydrates (soil microorganisms) and polymers, carboxylic and ketone acids (river microorganisms). Hydrolates could be an alternative to conventional antibiotics, but their impact on the environment must be taken into account.

Impact of eight widely consumed antibiotics on the growth and physiological profile of natural soil microbial communities.

Antibiotics' (ATBs) occurrence in soil ecosystems has a relevant effect in the structure and functionality of edaphic microbial communities, mainly because of their amendment with manure and biosolids that alter their key ecological functions. In this study, the impact of eight widely consumed ATBs on a natural soil microbial community, characterized through 16 S rRNA gene sequencing, was evaluated. Changes induced by the ATBs in the growth of the soil microbiota and in the community-level physiological profiling (CLPP), using Biolog EcoPlates™, were measured as endpoint. The eight assayed ATBs lead to a significant decrease in the growth of soil microbial communities in a dose-dependent way, ordered by its effect as follows: chloramphenicol > gentamycin > erythromycin > ampicillin > penicillin > amoxicillin > tetracycline > streptomycin. Chloramphenicol, gentamycin, and erythromycin adversely affected the physiological profile of the soil community, especially its ability to metabolize amino acids, carboxylic and ketonic acids and polymers. The analysis of the relationship between the physico-chemical properties of ATBs, as well as their mechanism of action, revealed that, except for the aminoglycosides, each ATB is influenced by a different physico-chemical parameters, even for ATBs of the same family. Significant effects were detected from 100 µg mL to 1, concentrations that can be found in digested sludge, biosolids and even in fertilized soils after repeated application of manure, so cumulative and long-term effects of these antibiotics on soil environment cannot be ruled out.

Impact of citronellol on river and soil environments using non-target model organisms and natural populations.

Citronellol is an acyclic monoterpenoid with a wide range of pharmacological activities (antibacterial, antifungal, anti-lice, repellent, lipolytic, anti-allergic, anti-inflammatory, antispasmodic, antidiabetic, anti-cholesterol, among other) and potential to replace synthetic products. However, the impact of citronellol on the environment remains unknown. We analysed, for the first time, the environmental impact of citronellol on river and soil environments using non-target model organisms and natural populations. The acute toxicity of citronellol on the aquatic invertebrate Daphnia magna, the plant Allium cepa L and the earthworm Eisenia fetida was quantified. The effect of citronellol in a river ecosystem was analysed using river periphyton communities taxonomically characterised and a river microbial community characterised through 16 S rRNA gene sequencing. Finally, a microbial community from natural soil was used to monitor the effect of citronellol on the soil ecosystem. The results showed that E. fetida was most sensitive to citronellol (LC50 = 12.34 mg/L), followed by D. magna (LC50 = 14.11 mg/L). Citronellol affected the photosynthesis of the fluvial periphyton (LC50 = 94.10 mg/L) and was phytotoxic for A. cepa. Furthermore, citronellol modified the growth and metabolism of both fluvial (LC50 = 0.19% v/v) and edaphic (LC50 = 5.07% v/v) bacterial populations. The metabolism of the microorganisms in the soil and water exposed to citronellol decreased with respect to the control, especially their ability to metabolise carbohydrates. Our results show that citronellol has a negative impact on the environment. Although acute effects cannot be expected, it is necessary to quantify the environmental levels as well as the long-term and persistent effects of this monoterpene.

Effects of the insecticide fipronil in freshwater model organisms and microbial and periphyton communities.

Fipronil is a broad-spectrum insecticide whose release in the environment damages many non-target organisms. This study evaluated the toxicity of fipronil at two biological levels using in vivo conditions and environmentally relevant concentrations: the first based on two model organisms (aquatic invertebrate Daphnia magna and the unicellular freshwater alga Chlamydomonas reinhardtii) and a second based on three natural communities (river periphyton and freshwater and soil microbial communities). The physicochemical properties of fipronil make it apparently unstable in the environment, so its behaviour was followed with high performance liquid chromatography (HPLC) under the different test conditions. The most sensitive organism to fipronil was D. magna, with median lethal dose (LC50) values from 0.07 to 0.38 mg/L (immobilisation test). Toxicity was not affected by the media used (MOPS or river water), but it increased with temperature. Fipronil produced effects on the photosynthetic activity of C. reinhardtii at 20 °C in MOPS (EC50 = 2.44 mg/L). The freshwater periphyton presented higher sensitivity to fipronil (photosynthetic yield EC50 of 0.74 mg/L) in MOPS and there was a time-dependent effect (toxicity increased with time). Toxicity was less evident when periphyton and C. reinhardtii tests were performed in river water, where the solubility of fipronil is poor. Finally, the assessment of the metabolic profiles using Biolog EcoPlates showed that bacteria communities were minimally affected by fipronil. The genetic identification of these communities based on 16S rRNA gene sequencing revealed that many of the taxa are specialists in degrading high molecular weight compounds, including pesticides. This work allows us to better understand the impact of fipronil on the environment at different levels of the food chain and in different environmental conditions, a necessary point given its presence in the environment and the complex behaviour of this compound.

Impact of climate change on drought in Aragon (NE Spain).

Droughts are one of the extreme climatic phenomena with the greatest and most persistent impact on health, economic activities and ecosystems and are poorly understood due to their complexity. The exacerbation of global warming throughout this century probably will cause an increase in droughts, so accurate studies of future projections at a local level, not done so far, are essential. Climate change scenarios of drought indexes for the region of Aragon (Spain) based on nine Earth System Models (ESMs) and two Representative Concentration Pathways (RCPs) corresponding to the fifth phase of the Coupled Model Intercomparison Project (CMIP5) have been generated for the first time. Meteorological Drought episodes were analysed from three main aspects: magnitude (index values), duration and spatial extent. The evolution of drought is also represented in a novel way, allowing identification, simultaneously, of the intensity of the episodes as well as their duration in different periods of accumulation and, for the first time, at the observatory level. Future meteorological drought scenarios based on the Standardized Precipitation Index (SPI) hardly show variations in water balance with respect to normal values. However, the Standardized Precipitation Evapotranspiration Index (SPEI) which, in addition to precipitation, considers evapotranspiration, shows a clear trend towards increasingly intense periods of drought, especially when considering cumulative periods and those at the end of the century. Representation of the territory of the drought indexes reflects that the most populated areas (Ebro Valley and SW of the region), will suffer the longest and most intense drought episodes. These results are key in the development of specific measures for adapting to climate change.