Physiological response of Simocephalus vetulus to five antibiotics and their mixture under 48-h acute exposure

Multigenerational testing reveals delayed chronic toxicity of bisphenol A to Daphnia magna: A common characteristic of endocrine-disrupting chemicals?

Bisphenol A (BPA) poses longstanding environmental concerns due to its widespread presence and recognized toxicity; however, its multigenerational ecotoxicity, in aquatic models such as water fleas, remains incompletely understood. This study examined the impact of sublethal BPA exposure on Daphnia magna across six generations, tracking changes in both life-history and population traits. Over the first five generations, BPA exposure produced minor and inconsistent effects on age at first oogenesis, age at first offspring production, growth rate, and fertility. The sixth generation exhibited prolonged oogenesis, delayed first offspring production, reduced body size, and decreased fertility, indicating delayed adverse effects. These multigenerational effects did not significantly alter population size or dynamics. Furthermore, BPA exposure did not affect feeding behavior in D. magna over six days, suggesting that food consumption-mediated mechanisms were unlikely a contributing factor. Our findings reveal BPA's delayed adverse effects on D. magna fitness, underscoring potential vulnerabilities for D. magna and other species under additional environmental stressors. These results support literature indicating that endocrine-disrupting chemicals can cause delayed and cumulative adverse effects on zooplankton descendants. Broadening multigenerational research to include a wider range of species, alongside sub-organismal analyses, is crucial to advancing regulatory frameworks and understanding underlying mechanisms.

Multigenerational ecotoxicity of tris(2-butoxyethyl) phosphate to the tropical water flea Ceriodaphnia cornuta and probabilistic ecological risk assessment in freshwater environments

The widespread use of the organophosphorus flame retardant tris(2-butoxyethyl) phosphate (TBOEP) and its presence in aquatic environments pose a hazard to wildlife. This study investigates the chronic ecotoxicity of TBOEP at environmentally relevant concentrations (6 ± 0.7 µg L-1) in the tropical water flea Ceriodaphnia cornuta over seven generations. Delayed toxicity emerged from the second generation (F1) to the fourth generation (F3), affecting survival, body length, and fertility. Recovery occurred in F4, followed by complete inhibition in F5 and F6, where no organisms survived beyond day 10. Population dynamics revealed minimal growth in F5, leading to extinction by F6. This is the first study to demonstrate the multigenerational lethal effects of TBOEP at environmentally relevant concentrations, highlighting ecological threats to C. cornuta and other sensitive species. The mechanisms underlying these effects remain unclear and require sub-organismal investigation. The chronic predicted no-effect concentration, estimated at 8.64 µg L-1, exceeds the tested concentration and therefore may not adequately protect vulnerable species. Ecological risk assessments based on TBOEP concentrations detected in surface waters since 2014 suggest potential risks at elevated levels in specific locations across multiple countries. Additional research is essential to validate TBOEP's toxicity across species under chronic and multigenerational exposure. Current ecological risk assessments likely underestimate TBOEP's threat to aquatic ecosystems, emphasizing the need for reassessment to better safeguard biodiversity.

Weak salinization alleviates the harmful impact of cyanobacteria on water fleas

Climate change and anthropogenic activities are driving dramatic changes in aquatic ecosystems. In this context, cyanobacterial blooms and freshwater salinization have recently received much attention, however, the comprehensive effects of these stressors on aquatic organisms are complex and have yet to be accurately clarified. This study tested the harmful effects of cyanobacteria and increasing salinity on zooplankton by characterizing the life-history traits and gut microbiota composition in the large-bodied Daphnia pulex and small-bodied Simocephalus vetulus. In 0 g L-1 salinity, the intrinsic growth rates of both species decreased when fed a diet containing cyanobacteria. Without cyanobacteria, the intrinsic growth rate of D. pulex was highest at 1 g L-1 salinity and lowest at 2 g L-1, whereas that of S. vetulus declined as salinity levels rose. Salinity alleviated the negative effects of cyanobacteria on water fleas. D. pulex performed worse than S. vetulus under high salinity (2 g L-1), cyanobacteria or their combined effects. Salinity changed the dominant gut microbiota in the water fleas when fed cyanobacteria. Bacteroides sp. and Cetobacterium sp. in D. pulex and Cetobacterium sp. in S. vetulus were most abundant when the water fleas were reared at low salinity (1 g L-1). The consistent changes in the dominant bacterial groups and the life-history traits indicate that the gut microbiota might adjust their tolerance to cyanobacteria.

Newly developed antibiotics against multidrug-resistant and carbapenem-resistant Gram-negative bacteria: action and resistance mechanisms

Antimicrobial resistance stands as one of the most urgent global health concerns in the twenty-first century, with projections suggesting that deaths related to drug-resistant infections could escalate to 10 million by 2050 if proactive measures are not implemented. In intensive care settings, managing infections caused by multidrug-resistant (MDR) Gram-negative bacteria is particularly challenging, posing a significant threat to public health and contributing substantially to both morbidity and mortality. There are numerous studies on the antibiotics responsible for resistance in Gram-negative bacteria, but comprehensive research on resistance mechanisms against new antibiotics is rare. Considering the possibility that antibiotics may no longer be effective in combating diseases, it is crucial to comprehend the problem of emerging resistance to newly developed antibiotics and to implement preventive measures to curb the spread of resistance. Mutations in porins and efflux pumps play a crucial role in antibiotic resistance by altering drug permeability and active efflux. Porin modifications reduce the influx of antibiotics, whereas overexpression of efflux pumps, particularly those in the resistance-nodulation-cell division (RND) family, actively expels antibiotics from bacterial cells, significantly lowering intracellular drug concentrations and leading to treatment failure.This review examines the mechanisms of action, resistance profiles, and pharmacokinetic/pharmacodynamic characteristics of newly developed antibiotics designed to combat infections caused by MDR and carbapenem-resistant Gram-negative pathogens. The antibiotics discussed include ceftazidime-avibactam, imipenem-relebactam, ceftolozane-tazobactam, meropenem-vaborbactam, aztreonam-avibactam, delafloxacin, temocillin, plazomicin, cefiderocol, and eravacycline.

Hepatotoxicity, developmental toxicity, and neurotoxicity risks associated with co-exposure of zebrafish to fluoroquinolone antibiotics and tire microplastics: An in silico study

This study aimed to investigate the differences in the mechanisms of microscopic hepatotoxicity, developmental toxicity, and neurotoxicity in aquatic organisms co-exposed to styrene-butadiene rubber tire microplastics (SBR TMPs) and fluoroquinolone antibiotics (FQs). We found that hepatotoxicity in zebrafish induced by SBR TMPs and FQs was significantly higher than developmental toxicity and neurotoxicity. Furthermore, the main effects of the FQs primarily manifested as synergistic toxicity, whereas the low- and high-order interactions of the FQs mainly exhibited synergistic and antagonistic effects, respectively. Factorial analysis and the mixture toxicity index revealed that the synergistic effects of lomefloxacin × moxifloxacin and ciprofloxacin × lomefloxacin × enrofloxacin interactions significantly contributed to hepatotoxicity in zebrafish exposed to SBR TMP. SBR TMPs and antibiotics primarily induced hepatotoxicity, developmental toxicity, and neurotoxicity in zebrafish by affecting the activities of Cyp1a, Acox1, TRα, and mAChR. The observed toxicities were closely linked to the hydrophilic/hydrophobic groups, electronegativity, group mass, and structural complexity of the FQ molecules. This study provides new insights regarding the toxicological risks to aquatic organisms from co-exposure to SBR TMPs and FQs from a microscopic perspective. Future studies should include a broader range of antibiotics and tire microplastics and consider their long-term adverse effects on aquatic life.

Toxicity of ciprofloxacin and ofloxacin to Moina macrocopa and investigation of p-value adjustments for (eco)toxicological studies

Ciprofloxacin (CFX) and ofloxacin (OFX) are commonly found as residual contaminants in aquatic environments, posing potential risks to various species. To ensure the safety of aquatic wildlife, it is essential to determine the toxicity of these antibiotics and establish appropriate concentration limits. Additionally, in (eco)toxicological studies, addressing the issue of multiple hypothesis testing through p-value adjustments is crucial for robust decision-making. In this study, we assessed the no observed adverse effect concentration (NOAEC) of CFX and OFX on Moina macrocopa across a concentration range of 0-400 µg L-1. Furthermore, we investigated multiple p-value adjustments to determine the NOAECs. Our analysis yielded consistent results across seven different p-value adjustments, indicating NOAECs of 100 µg CFX L-1 for age at first reproduction and 200 µg CFX L-1 for fertility. For OFX treatment, a NOAEC of 400 µg L-1 was observed for both biomarkers. However, further investigation is required to establish the NOAEC of OFX at higher concentrations with greater certainty. Our findings demonstrate that CFX exhibits higher toxicity compared to OFX, consistent with previous research. Moreover, this study highlights the differential performance of p-value adjustment methods in terms of maintaining statistical power while controlling the multiplicity problem, and their practical applicability. The study emphasizes the low NOAECs for these antibiotics in the zooplanktonic group, highlighting their significant risks to ecological and environmental safety. Additionally, our investigation of p-value adjustment approaches contributes to a deeper understanding of their performance characteristics, enabling (eco)toxicologists to select appropriate methods based on their specific needs and priorities.

Ecotoxicity of the fluoroquinolone antibiotic delafloxacin to the water flea Simocephalus vetulus and its offspring under the influence of calcium modulation

Delafloxacin (DFX), one of the latest additions to the fluoroquinolone antibiotics, is gaining heightened recognition in human therapy due to its potential antibacterial efficacy in a wide range of applications. Concerns have arisen regarding its presence in the environment and its potential interactions with multivalent metals, such as calcium (Ca). The present study investigated the trans- and multigenerational effects of environmentally projected concentrations of DFX (100-400 μg DFX L-1) on individual- and population-level responses of parental S. vetulus (F0) and its descendants (F1) under normal (26 mg L-1) and high (78 mg L-1) Ca conditions. Exposure of the F0 generation to DFX under the normal Ca condition resulted in reduced juvenile body length (JBL), increased age-specific survival rate (lx), indicating prolonged developmental time, reduced age-specific fecundity rate (mx), and decreased population growth rate (rm). Under the high Ca condition, JBL, mx, and rm were adversely affected. Transgenerational effects of DFX existed, as F1 individuals exhibited persistent suppressions in at least one endpoint under both Ca conditions even after being transferred to a clear medium. Continuous exposure of the F1 generation to DFX had negative impacts on JBL, mx, and rm under the normal Ca condition, and on JBL and rm under the high Ca condition. However, cumulative effects were not observed, suggesting the potential development of tolerance to DFX in the F1 organisms. These findings suggest that DFX is a harmful compound for the non-target model organism S. vetulus and reveal a potential antagonism between DFX and Ca. Nevertheless, the interaction between other (fluoro)quinolones and Ca remains unclear, necessitating further research to establish this phenomenon more comprehensively, including understanding the interaction mechanism in ecotoxicological contexts.

Antibiotic Pollution of Planktonic Ecosystems: A Review Focused on Community Analysis and the Causal Chain Linking Individual- and Community-Level Responses

Antibiotic pollution has become one of the most challenging environmental issues in aquatic ecosystems, with adverse effects on planktonic organisms that occupy the base of the aquatic food chain. However, research regarding this topic has not been systematically reviewed, especially in terms of community-level responses. In this review, we provide an overview of current antibiotic pollution in aquatic environments worldwide. Then, we summarize recent studies concerning the responses of planktonic communities to antibiotics, ranging from individual- to community-level responses. Studies have shown that extremely high concentrations of antibiotics can directly harm the growth and survival of plankton; however, such concentrations are rarely found in natural freshwater. It is more likely that environmentally relevant concentrations of antibiotics will affect the physiological, morphological, and behavioral characteristics of planktonic organisms; influence interspecific interactions among plankton species via asymmetrical responses in species traits; and thus alter the structure and function of the entire planktonic ecosystem. This review highlights the importance of community analysis in revealing antibiotic toxicity. We also encourage the establishment of the causal relationships between impacts at multiple scales in the future for predicting the community-level consequences of antibiotics based on the currently available individual-level evidence.

Delafloxacin-Capped Gold Nanoparticles (DFX-AuNPs): An Effective Antibacterial Nano-Formulation of Fluoroquinolone Antibiotic

New antibiotics are seen as 'drugs of last resort' against virulent bacteria. However, development of resistance towards new antibiotics with time is a universal fact. Delafloxacin (DFX) is a new fluoroquinolone antibiotic that differs from existing fluoroquinolones by the lack of a protonatable substituent, which gives the molecule a weakly acidic nature, affording it higher antibacterial activity under an acidic environment. Furthermore, antibiotic-functionalized metallic nanoparticles have been recently emerged as a feasible platform for conquering bacterial resistance. In the present study, therefore, we aimed at preparing DFX-gold nano-formulations to increase the antibacterial potential of DFX. To synthesize DFX-capped gold nanoparticles (DFX-AuNPs), DFX was used as a reducing and stabilizing/encapsulating agent. Various analytical techniques such as UV-visible spectroscopy, TEM, DLS, FTIR and zeta potential analysis were applied to determine the properties of the synthesized DFX-AuNPs. The synthesized DFX-AuNPs revealed a distinct surface plasmon resonance (SPR) band at 530 nm and an average size of 16 nm as manifested by TEM analysis. In addition, Zeta potential results (-19 mV) confirmed the stability of the synthesized DFX-AuNPs. Furthermore, FTIR analysis demonstrated that DFX was adsorbed onto the surface of AuNPs via strong interaction between AuNPs and DFX. Most importantly, comparative antibacterial analysis of DFX alone and DFX-AuNPs against Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus and Bacillus subtilis) verified the superior antibacterial activity of DFX-AuNPs against the tested microorganisms. To sum up, DFX gold nano-formulations can offer a promising possible solution, even at a lower antibiotic dose, to combat pathogenic bacteria.