Antibiotic risk assessment needs to protect both environmental and human health

Highly sensitive and selective detection of amoxicillin using molecularly imprinted ratiometric fluorescent nanosensor based on quantum dots

A dual-emission ratiometric fluorescence sensor (CDs@CdTe@MIP) with a self-calibration function was successfully constructed for AMO detection. In the CDs@CdTe@MIP system, non-imprinted polymer-coated CDs and molecule-imprinted polymer-coated CdTe quantum dots were used as the reference signal and response elements, respectively. The added AMO quenched the fluorescence of the CdTe quantum dots, whereas the fluorescence intensity of the CDs remained almost unchanged. The AMO concentration was monitored using the fluorescence intensity ratio (log(I647/I465)0/(I647/I465)) to reduce interference from the testing environment. The sensor with a low detection limit of 0.15 μg/L enabled detection of the AMO concentration within 6 min. The ratiometric fluorescence sensor was used to detect AMO in spiked pork samples; it exhibited a high recovery efficiency and relative standard deviation (RSD) of 97.94-103.70% and 3.77-4.37%, respectively. The proposed highly sensitive and selective platform opens avenues for sensitive, reliable, and rapid determination of pharmaceuticals in the environment and food safety monitoring using ratiometric sensors.

Effects of antibiotics consumption on the behavior of airborne antibiotic resistance genes in chicken farms

The antibiotics and antibiotic resistance genes (ARGs) have caused pollution of livestock farm environments. There are limited investigations about airborne ARGs and what role the antibiotics play remains largely unclear. The dynamics of various antibiotics were compared between feces samples from chicken fed a diet with and without antibiotics. In contrast to the farm with no antibiotics drugs, the hazard quotients (HQs) of OTC (24.8-205.4) and CTC (18.0-317.0) are particularly high in the farm with in-feed antibiotics drugs. The high ecological risks of antibiotics in chicken feces with in-feed antibiotic drugs were 100 % as determined. We quantified mobile genetic elements (MGEs) and ARGs and investigated bacterial communities in feces and air samples. The concentration of airborne ARG/MGE subtypes with in-feed antibiotic drugs is about two orders of magnitude higher than those without drugs. This study reveals that the indoor air of chicken farms is a reservoir of ARGs in the environment. Continuous feeding of antibiotics can change the intestinal microbial community structure of the chicken. The possibility of horizontal gene transfer of ARGs in air and feces samples might be increased by in-feed antibiotic drugs. The enrichment of ARGs in the chicken farm can be reduced by minimizing antibiotic use.

Occurrence, detection and ecotoxicity studies of selected pharmaceuticals in aqueous ecosystems- a systematic appraisal

Pharmaceutical compounds (PCs) have globally emerged as a significant group of environmental contaminants due to the constant detection of their residues in the environment. The main scope of this review is to fill the void of information on the knowledge on the African occurrence of selected PCs in environmental matrices in comparison with those outside Africa and their respective toxic actions on both aquatic and non-aquatic biota through ecotoxicity bioassays. To achieve this objective, the study focused on commonly used and detected pharmaceutical drugs (residues). Based on the conducted literature survey, Africa has the highest levels of ciprofloxacin, sulfamethoxazole, lamivudine, acetaminophen, and diclofenac while Europe has the lowest of all these PC residues in her physical environments. For ecotoxicity bioassays, the few data available are mostly on individual groups of pharmaceuticals whereas there is sparsely available data on their combined forms.

Impact of sulfamethoxazole on a riverine microbiome

The continued emergence of bacterial pathogens presenting antimicrobial resistance is widely recognised as a global health threat and recent attention focused on potential environmental reservoirs of antibiotic resistance genes (ARGs). Freshwater environments such as rivers represent a potential hotspot for ARGs and antibiotic resistant bacteria as they are receiving systems for effluent discharges from wastewater treatment plants (WWTPs). Effluent also contains low levels of different antimicrobials including antibiotics and biocides. Sulfonamides are antibacterial chemicals widely used in clinical, veterinary and agricultural settings and are frequently detected in sewage sludge and manure in addition to riverine ecosystems. The impact of such exposure on ARG prevalence and diversity is unknown, so the aim of this study was to investigate the release of a sub-lethal concentration of the sulfonamide compound sulfamethoxazole (SMX) on the river bacterial microbiome using a flume system. This system was a semi-natural in vitro flume using river water (30 L) and sediment (6 kg) with circulation to mimic river flow. A combination of 'omics' approaches were conducted to study the impact of SMX exposure on the microbiomes within the flumes. Metagenomic analysis showed that the addition of low concentrations of SMX (<4 μg L^-1) had a limited effect on the bacterial resistome in the water fraction only, with no impact observed in the sediment. Metaproteomics did not show differences in ARGs expression with SMX exposure in water. Overall, the river bacterial community was resilient to short term exposure to sub-lethal concentrations of SMX which mimics the exposure such communities experience downstream of WWTPs throughout the year.

Evaluation of frameworks proposed as protective of antimicrobial resistance propagation in the environment

Antimicrobial resistance (AMR) in the environment is a globally concerning issue. This study sought to improve the understanding of human health risks from an environmental AMR proliferation perspective. Surface water concentrations of 11 most used antibiotics in the United States were simulated for the Columbia and Sacramento River watersheds using the Pharmaceutical Assessment and Transport Evaluation (PhATE) model. The predicted environmental concentrations (PECs) and literature-reported measured environmental concentrations (MECs) of antibiotics were compared to the predicted no effect concentrations (PNECs) of three frameworks proposed as protective of AMR selection. For all of the studied antibiotics, PECs (except for moxifloxacin, a 4th generation fluoroquinolone), and at least one published MEC, were above the safe limit proposed by at least one of the three frameworks. The results indicate that a variety of different antibiotics with different mechanisms of action and physico-chemical properties are likely in environmental compartments at or above the concentrations currently proposed as safe from an AMR proliferation perspective. Understanding environmental occurrence of antibiotics is important for assessing environmental exposures and, when compared to PNECs for resistance selection, can-either alone or in combination with other methods- more specifically indicate where there are potential risks of AMR proliferation.

Evaluation of factors influencing annual occurrence, bioaccumulation, and biomagnification of antibiotics in planktonic food webs of a large subtropical river in South China

Biological pump is important to control the fate and distribution of organic contaminants, particularly in temperate and cold oligotrophic waters. However, it remains largely unknown how factors affect the long-term occurrence and fate of ionogenic organic compounds in subtropical eutrophic waters. The present study aimed to assess biogeochemical and physical factors affecting the annual occurrence, bioaccumulation, and trophic transfer of 14 antibiotics through planktonic food webs in the Pearl River, a large subtropical eutrophic river in China. This was done by carrying out 1-year simultaneous field observations of antibiotic concentrations in five water column compartments and assessing the variability of bioconcentration (BCF), bioaccumulation (BAF), and biomagnification (BMF) factors, which were influenced by plankton biomass, pH and temperature of water columns. The annual mean antibiotic concentration per site ranged from 1014.66 ± 535.66 ng L^-1 to 1464.63 ± 1075.91 ng L^-1, and was positively correlated with phytoplankton biomass, but independent of the proximity of the sites to urban areas. Antibiotic occurrences in both phytoplankton and zooplankton were greatly influenced by a biodilution effect. The annual occurrence of antibiotics in the water column was modulated by biological pumps as well as their equilibrium partitioning, and indirectly influenced of eutrophication with pH increased with phytoplankton biomass and phytoplankton life cycling. BAF of antibiotics by plankton had biphasic correlations with temperature (n = 150, R² = 0.17-0.60, p < 0.001) and decreased with plankton biomass (n = 105-147, R² = 0.10-0.22, p < 0.001). The trophic transfer of antibiotics from phytoplankton to zooplankton (BMFs) were positively correlated with both phytoplankton biomass (n = 30, R² = 0.58, p < 0.001) and temperature (n = 132-150, R² = 0.12-0.43, p < 0.001). Mean BMFs of ciprofloxacin, lomefloxacin, ofloxacin, oxytetracycline, and tetracycline ranged between 0.18 and 2.25, implying these chemicals can undergo biomagnification along planktonic food webs. The present research demonstrates the important role of biogeochemical and physical factors in the environmental fate of antibiotics at large spatiotemporal scales.

Variability in cyanobacteria sensitivity to antibiotics and implications for environmental risk assessment

Once released into the environment antibiotics can kill or inhibit the growth of bacteria, and in turn potentially have effects on bacterial community structure and ecosystem function. Environmental risk assessment (ERA) seeks to establish protection limits to minimise chemical impacts on the environment, but recent evidence suggests that the current regulatory approaches for ERA for antibiotics may not be adequate for protecting bacteria that have fundamental roles in ecosystem function. In this study we assess the differences in interspecies sensitivity of eight species of cyanobacteria to seven antibiotics (cefazolin, cefotaxime, ampicillin, sufamethazine, sulfadiazine, azithromycin and erythromycin) with three different modes of action. We found that variability in the sensitivity to these antibiotics between species was dependent on the mode of action and varied by up to 70 times for β-lactams. Probabilistic analysis using species sensitivity distributions suggest that the current predicted no effect concentration PNEC for the antibiotics may be either over or under protective of cyanobacteria dependent on the species on which it is based and the mode of action of the antibiotic; the PNECs derived for the macrolide antibiotics were over protective but PNECs for β-lactams were generally under protective. For some geographical locations we identify a significant risk to cyanobacteria populations based upon measured environmental concentrations of selected antibiotics. We conclude that protection limits, as determined according to current regulatory guidance, may not always be protective and might be better derived using SSDs and that including toxicity data for a wider range of (cyano-) bacteria would improve confidence for the ERA of antibiotics.

A conceptual framework for the environmental surveillance of antibiotics and antibiotic resistance

Environmental surveillance of antibiotics and antibiotic resistance could contribute toward the protection of human, animal and ecosystem health. However, justification for the choice of markers and sampling sites that informs about different risk scenarios is often lacking. Here, we define five fundamentally different objectives for surveillance of antibiotics and antibiotic resistance in the environment. The first objective is (1) to address the risk of transmission of already antibiotic-resistant bacteria to humans via environmental routes. The second is (2) to address the risk for accelerating the evolution of antibiotic resistance in pathogens through pollution with selective agents and bacteria of human or animal origin. The third objective is (3) to address the risks antibiotics pose for aquatic and terrestrial ecosystem health, including the effects on ecosystem functions and services. The two final objectives overlap with those of traditional clinical surveillance, namely, to identify (4) the population-level resistance prevalence and (5) population-level antibiotic use. The latter two environmental surveillance objectives have particular potential in countries where traditional clinical surveillance data and antibiotic consumption data are scarce or absent. For each objective, the levels of evidence provided by different phenotypic and genotypic microbial surveillance markers, as well as antibiotic residues, are discussed and evaluated on a conceptual level. Furthermore, sites where monitoring would be particularly informative are identified. The proposed framework could be one of the starting points for guiding environmental monitoring and surveillance of antibiotics and antibiotic resistance on various spatiotemporal scales, as well as for harmonizing such activities with existing human and animal surveillance systems.