We have been using and misusing antibiotics for years both in human and veterinary medicine. Residues of antibiotics are released from wastewaters to the environment where they enhance the spread of antibiotic resistance. This is why several antibiotic-resistant superbug strains are emerging around the world and putting the health system under a lot of pressure. To circumvent this problem, we need to better understand what triggers the spread of antibiotic resistance and which other factors impact it. The review “Knowledge gaps in the assessment of antimicrobial resistance in surface waters” published in FEMS Microbiology Ecology highlights how antimicrobial resistance emerges from the environment and how it is linked to our activities. Magdalena Niegowska explains for the #FEMSmicroBlog why we need to pay attention to the interplay of resistances in the environment. #FascinatingMicrobes
About the antibiotic resistance problem
In recent years, the World Health Organization included the antibiotic resistance phenomenon among the main threats to global health. Yet, we currently don’t understand the whole picture of the selection pressure from antibiotics and co-occurring substances.
Especially wastewater treatment plants are often not able to completely remove antibiotic residues, resistance genes and antibiotic-resistant bacteria. Hence, these pollutants are collected in surface waters thus allowing their long-distance diffusion. Together with other chemical substances, they favor the development of co-resistances.
Wastewater treatment plants often don’t completely remove antibiotic residues, resistance genes and antibiotic-resistant bacteria thus allowing their long-distance diffusion.
The review “Knowledge gaps in the assessment of antimicrobial resistance in surface waters” published in FEMS Microbiology Ecology explores this phenomenon. It outlines how antibiotics and heavy metals exert pressure on aquatic environments and impact the spread of antimicrobial resistance. Furthermore, the role of microplastics in co-selection for metal and antibiotic resistance are highlighted.
At the policy level, no safety threshold or standardized guidelines on the environmental risk assessment of antibiotics exist currently. This is largely due to insufficient data on environmentally relevant concentrations.
Current European legislation on water quality includes monitoring five antibiotics individually while neglecting the effects of co-occurring substances. Furthermore, their concentrations, and whether considered safe for aquatic organisms and indirectly for humans, are estimated based on toxicological properties. While these include their abilities to limit the growth of organisms, this does not take into account the spread of antibiotic resistance genes or the threat of resistant infections.
Antimicrobial resistance can originate in the environment
The transfer of antibiotic resistance genes is clearly linked to clinical settings and environmental compartments impacted by human activities. Yet, it is not evident that antibiotic concentrations affect the transfer of resistance genes. Hence, it may as well be affected by several other factors.
To fully understand how antibiotic resistance genes are acquired and transferred, possible paths and relationships should be assessed as a whole. At the same time, investigating natural resistance is crucial to establishing the abundance of antibiotic-resistant bacteria and resistance genes in the environmental background. This would work as a reference point to understand how human activities impact the spread of antimicrobial resistance. Even though the presence of antibiotics and resistance genes in impacted environments is widely discussed, the phenomenon of the transfer of antibiotic resistance genes in pristine areas is still poorly described.
In addition to antibiotics, other substances may impact antimicrobial resistance. While microbial species in the environment can become resistant to metals, the relationship between metals, antibiotics and the antimicrobial resistance spread is becoming clear.
There is evidence that sub-inhibitory concentrations of heavy metals in water environments trigger mutation rates and the horizontal transfer of antibiotic resistance genes. At environmentally relevant levels, heavy metals could even induce resistance to antibiotics.
About the lack of knowledge of antimicrobial resistances
Risk assessment of antibiotics in surface waters remains a complex question due to multiple variables and the lack of harmonized protocols. In particular, more research is needed to determine the environmental concentration at which antibiotics trigger antibiotic-sensitive bacteria to acquire resistance genes.
We still don’t know at which environmental concentration antibiotics trigger antibiotic-sensitive bacteria to acquire resistance genes.
The impact of heavy metals and other selective agents on antimicrobial resistances needs also to be defined. At the policy level, safety thresholds for antibiotics should be established to protect from the risk of antimicrobial resistance spread and, in consequence, untreatable infections.
- Read the article “Knowledge gaps in the assessment of antimicrobial resistance in surface waters” by Niegowska et al. (2021).
Magdalena Niegowska is a biotechnologist with a PhD in microbiology specialized in assessing chemical and environmental agents in the context of risk posed to human and animal health. Her contributions to projects at the European Commission Joint Research Centre (JRC) are focused on, among others, antimicrobial resistance and mixture toxicity in surface waters, development of alternative methods for microbiological parameters in drinking and bathing waters as well as substances’ selection for the Watch List of the European Water Framework Directive.
About this blog section
The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.
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