The link between pharmaceuticals and cyanobacteria: a review regarding ecotoxicological, ecological, and sanitary aspects

Environmental risk assessment in the EU regulation of medicines for human use: an analysis of stakeholder perspectives on its current and future role

An environmental risk assessment (ERA) is mandatory for all applications for marketing authorisation of medicines in the European Union (EU). We investigated stakeholder perspectives on the role of the ERA in EU regulation of medicines for human use. We discuss the current position of the ERA and the current conduct and assessment of the ERA, such as the required expertise, data, and studies, its applicability to generic drugs, and its use in regulatory decision-making. We also discuss future perspectives, including extension of the ERA to cover antimicrobial resistance, improved risk mitigation, impact on 'over-the-counter' (OTC) status, and incorporation into reimbursement considerations.

Repeated Exposure Enhanced Toxicity of Clarithromycin on Microcystis aeruginosa Versus Single Exposure through Photosynthesis, Oxidative Stress, and Energy Metabolism Shift

Antibiotics are being increasingly detected in aquatic environments, and their potential ecological risk is of great concern. However, most antibiotic toxicity studies involve single-exposure experiments. Herein, we studied the effects and mechanisms of repeated versus single clarithromycin (CLA) exposure on Microcystis aeruginosa. The 96 h effective concentration of CLA was 13.37 μg/L upon single exposure but it reduced to 6.90 μg/L upon repeated exposure. Single-exposure CLA inhibited algal photosynthesis by disrupting energy absorption, dissipation and trapping, reaction center activation, and electron transport, thereby inducing oxidative stress and ultrastructural damage. In addition, CLA upregulated glycolysis, pyruvate metabolism, and the tricarboxylic acid cycle. Repeated exposure caused stronger inhibition of algal growth via altering photosynthetic pigments, reaction center subunits biosynthesis, and electron transport, thereby inducing more substantial oxidative damage. Furthermore, repeated exposure reduced carbohydrate utilization by blocking the pentose phosphate pathway, consequently altering the characteristics of extracellular polymeric substances and eventually impairing the defense mechanisms of M. aeruginosa. Risk quotients calculated from repeated exposure were higher than 1, indicating significant ecological risks. This study elucidated the strong influence of repeated antibiotic exposure on algae, providing new insight into antibiotic risk assessment.

Interplays between cyanobacterial blooms and antibiotic resistance genes

Cyanobacterial harmful algal blooms (cyanoHABs), which are a form of microbial dysbiosis in freshwater environments, are an emerging environmental and public health concern. Additionally, the freshwater environment serves as a reservoir of antibiotic resistance genes (ARGs), which pose a risk of transmission during microbial dysbiosis, such as cyanoHABs. However, the interactions between potential synergistic pollutants, cyanoHABs, and ARGs remain poorly understood. During cyanoHABs, Microcystis and high microcystin levels were dominant in all the nine regions of the river sampled. The resistome, mobilome, and microbiome were interrelated and linked to the physicochemical properties of freshwater. Planktothrix and Pseudanabaena competed with Actinobacteriota and Proteobacteria during cyanoHABs. Forty two ARG carriers were identified, most of which belonged to Actinobacteriota and Proteobacteria. ARG carriers showed a strong correlation with ARGs density, which decreased with the severity of cyanoHAB. Although ARGs decreased due to a reduction of ARG carriers during cyanoHABs, mobile gene elements (MGEs) and virulence factors (VFs) genes increased. We explored the relationship between cyanoHABs and ARGs for potential synergistic interaction. Our findings demonstrated that cyanobacteria compete with freshwater commensal bacteria such as Actinobacteriota and Proteobacteria, which carry ARGs in freshwater, resulting in a reduction of ARGs levels. Moreover, cyanoHABs generate biotic and abiotic stress in the freshwater microbiome, which may lead to an increase in MGEs and VFs. Exploration of the intricate interplays between microbiome, resistome, mobilome, and pathobiome during cyanoHABs not only revealed that the mechanisms underlying the dynamics of microbial dysbiosis but also emphasizes the need to prioritize the prevention of microbial dysbiosis in the risk management of ARGs.

Cyanobacterial blooms: A player in the freshwater environmental resistome with public health relevance?

Cyanobacterial harmful algal blooms (cyanoHABs) are an ecological concern because of large ecosystem-disrupting blooms and a global public health concern because of the cyanotoxins produced by certain bloom-forming species. Another threat to global public health is the dissemination of antibiotic resistance (AR) in freshwater environmental reservoirs from anthropogenic sources, such as wastewater discharge and urban and agricultural runoff. In this study, cyanobacteria are now hypothesized to play a role in the environmental resistome. A non-systematic literature review of studies using molecular techniques (such as PCR and metagenomic sequencing) was conducted to explore indirect and direct ways cyanobacteria might contribute to environmental AR. Results show cyanobacteria can host antibiotic resistance genes (ARGs) and might promote the spread of ARGs in bacteria due to the significant contribution of mobile genetic elements (MGEs) located in genera such as Microcystis. However, cyanobacteria may promote or inhibit the spread of ARGs in environmental freshwater bacteria due to other factors as well. The purpose of this review is to 1) consider the role of cyanobacteria as AR hosts, since cyanoHABs are historically considered to be a separate problem from AR, and 2) to identify the knowledge gap in understanding cyanobacteria as ARG reservoirs. Cyanobacterial blooms, as well as other biotic (e.g. interactions with protists or cyanophages) and abiotic factors, should be studied further using advanced methods such as shotgun metagenomic and long read sequencing to clarify the extent of their functional ARGs/MGEs and influences on environmental AR.

The growth, biochemical composition, and antioxidant response of Microcystis and Chlorella are influenced by Ibuprofen

Non-steroidal anti-inflammatory drugs like ibuprofen (IBU) are extensively used, causing substantial amounts to end up in aquatic ecosystems. Unfortunately, little research has been done on how these medications influence the physiology of phytoplankton. This study aimed to investigate the toxicological and physiological effects of IBU on the cyanobacteria Microcystis aeruginosa LE3 and Microcystis aeruginosa EAWAG 198, and the chlorophyte Chlorella sorokiniana. Exponential growth phase cultures were exposed to IBU at 10 to 10,000 μg/L for 96 h. The medium effect concentrations revealed varied sensitivity to IBU in the order Chlorella sorokiniana > Microcystis aeruginosa LE3 > Microcystis aeruginosa EAWAG 198. The drug caused a significant difference from control in cell density and chlorophyll-a of the three strains, except for chlorophyll-a in M. aeruginosa EAWAG 198 cultures where a significant difference occurred at 100 μg/L. The cell density of M. aeruginosa LE3 cultures exposed to 10 μg/L IBU increased 24 h post-exposure. Increasing concentrations of IBU induced higher total microcystins content of the Microcystis aeruginosa. Intracellular hydrogen peroxide content, peroxidase, and glutathione S-transferase activities, and lipid peroxidation increased as a function of IBU exposure. Total lipid, carbohydrate, and protein content of Chlorella sorokiniana were stimulated following IBU exposure. We conclude that the increasing presence of IBU in aquatic ecosystems could significantly alter the population dynamics of the investigated and other phytoplankton species.

Antibiotic-accelerated cyanobacterial growth and aquatic community succession towards the formation of cyanobacterial bloom in eutrophic lake water

Antibiotics can stimulate the growth of model cyanobacterial species under pure culture conditions, but their influence on cyanobacterial blooms in natural aquatic ecosystems remains unclear. In this study, three commonly detected antibiotics (sulfamethoxazole, tetracycline, and ciprofloxacin) and their ternary mixture were proved to selectively stimulate (p < 0.05) the growth and photosynthetic activity of cyanobacteria in an aquatic microcosm at an environmentally relevant exposure dose of 300 ng/L under both oligotrophic and eutrophic conditions. Under the eutrophic condition, cyanobacteria reached a bloom density of 1.61 × 10⁶ cells/mL in 15 days without antibiotics, while the cyanobacteria exposed to tetracycline, sulfamethoxazole, ciprofloxacin, and their ternary mixture exceeded this bloom density within only 10, 8, 7, and 6 days, respectively. Principal coordinate analysis indicated that the antibiotic contaminants accelerated the prokaryotic community succession towards the formation of a cyanobacterial bloom by promoting the dominance of Microcystis, Synechococcus, and Oscillatoria under the eutrophic condition. After 15 days of culture, the antibiotic exposure increased the density of cyanobacteria by 1.38-2.31-fold and 2.28-3.94-fold under eutrophic and oligotrophic conditions, respectively. Antibiotic exposure generated higher stimulatory effects on cyanobacterial growth under the oligotrophic condition, but the antibiotic(s)-treated cyanobacteria did not form a bloom due to nutrient limitation. Redundancy analysis indicated that the three target antibiotics and their ternary mixture affected the prokaryotic community structure in a similar manner, while tetracycline showed some differences compared to sulfamethoxazole, ciprofloxacin, and the ternary antibiotic mixture with regard to the regulation of the eukaryotic community structure. This study demonstrates that antibiotic contaminants accelerate the formation of cyanobacterial blooms in eutrophic lake water and provides insights into the ecological effects of antibiotics on aquatic microbial communities.