In a new study, scientists at Phenikaa University, the Institute of Microbiology (VNU), the National Institute of Hygiene and Epidemiology, Yersin University and Heriot-Watt University have found the first evidence of antibiotic-resistant bacteria linked to microplastics in the Red River Delta.
Pic 1: The process of using plastic and discharging it into the environment leads to long-term impacts on the environment and human health.
Globally and in Vietnam, urbanisation, industrialisation, and intensive agriculture are altering the environment, leading to increased antimicrobial resistance (AMR) and posing a significant threat to global health. Antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) are detected in various environments and pose a significant health risk. Hospitals, agricultural areas and water treatment plants are all “hotspots” of ARB and ARGs due to the use of antibiotics in humans and livestock. This spreads ARB, including bacteria that produce extended-spectrum β-lactamases (ESBLs) that can produce enzymes that break down many antibiotics. Microplastics, meanwhile, pose a worrying environmental problem and are believed to act as vectors for the transmission and spread of ARGs and ARB. Their persistence and physicochemical properties allow them to act as vectors for transporting contaminants and antibiotic resistance to a wide range of microorganisms.
For many years, Vietnam has been facing a particularly high AMR burden due to the widespread use of antibiotics in human and veterinary health care, intensive aquaculture, and antibiotic use is not adequately controlled. According to many previous studies, alarming rates of resistance to β-lactams and other antibiotics have been identified in bacterial isolates.
Therefore, Vietnamese and British researchers decided to investigate the relationship between bacteria and microplastics in the Red River Delta and assess the presence of resistance genes, specifically those involved in the production of ESBLs. They aim to uncover valuable insights into the potential role of microplastics in the transmission of antibiotic resistance in the Red River Delta, a densely populated and economically dynamic region. Assessing the potential risks associated with microplastics and antibiotic resistance in the Red River Delta is crucial for designing and implementing new measures to mitigate these issues. The researchers found that although antibiotic resistance and microplastic contamination are essential and have impacts on the entire delta, they have not been thoroughly studied to date.
To conduct the study, they collected microplastics along the Red River Delta, including the middle region (Lien Ha, Dan Phuong, Hanoi) and the lower region (Ba Lat estuary and Xuan Thuy National Park, Nam Dinh), wastewater channels in the urban area of Hanoi and industrial zones (Ha Nam). Additionally, they collected samples in the surrounding regions, including Cat Ba Island. The samples were collected during the rainy season, from July to August 2023, a period known to have high concentrations of microplastics.
The results of the analysis of microplastic properties showed that the ageing process of microplastics in the environment increases surface roughness, promoting the formation of cracks and surface roughness, thereby promoting the invasion of bacteria. Conversely, hydrophobic surfaces can hinder close contact between microorganisms and microplastics. “This factor sheds light on our finding that PET polymer exhibits higher bacterial density on its surface due to its structure,” they reported in the paper.
The highest concentrations of bacteria on microplastics were detected in samples collected from surface water and bottom water in industrial zones, specifically Phu Ly, Ha Nam. Notably, the concentrations of bacteria on microplastics from water samples collected in Hanoi and Nam Dinh were consistently higher than those from Cat Ba Island. About 99.2% of them were bacteria belonging to the genus Aeromonas, including Aeromonas veronii and Aeromonas caviae. Only 0.83% were identified as E. coli, which were mainly detected in microplastics at water-receiving sites in Hanoi and some surrounding craft villages. Notably, the prevalence of Aeromonas spp. and E. coli from microplastics (90.8%) was higher than that of bacteria from the surrounding water environment (i.e. bacteria that did not adhere to microplastics). Previous studies have shown that microplastics can attract distinct bacterial communities compared to their surroundings, suggesting that microplastics may provide a unique substrate for bacterial survival. “Based on these findings, we hypothesise that microplastics may play an important role as carriers of ARBs and ARGs and their dissemination in aquatic environments,” the researchers wrote.
To further prove this hypothesis, they investigated three extended-spectrum β-Lactamase genes in the isolated bacterial strains and found that out of 207 bacteria isolated from microplastics, 23 contained antibiotic resistance genes, accounting for 11.1%. Notably, the highest proportion of isolates carrying resistance genes was found at the most polluted site, where wastewater from Hanoi and other traditional craft villages was concentrated, as well as at another site downstream of Hanoi and near industrial zones. The co-occurrence of all three resistance genes in bacteria isolated from microplastics at the Thanh Nhan Hospital water intake site.
Previous studies have demonstrated the presence of β-lactam-resistant bacteria, such as Aeromonas spp. and E. coli, along with their resistance genes, in soil, sediment, reservoirs, rivers, domestic wastewater, and hospitals. In addition, most (97%) ESBL-producing E. coli samples from hospitals contained at least one β-lactamase gene. These results suggest that river microplastics may act as reservoirs for antibiotic resistance factors, facilitating their survival and spread in aquatic environments.
When examining the correlation between bacterial density on microplastics and other environmental parameters, the researchers found that the presence of resistance genes was positively correlated with other environmental factors, including EC, salinity, and %OC. Salinity may influence the spread of resistance genes by affecting the bacterial community. High salinity environments may inhibit bacterial activity and growth, leading to higher bacterial concentrations in rivers such as Hanoi and Ha Nam, which have lower salinity levels than Cat Ba Island.
With these results, the researchers suggest that microplastics act as reservoirs for resistance genes, promoting their transport in biofilms. The Red River Delta is home to multi-resistant Aeromonas strains, highlighting the role of microplastics in the spread of antibiotic resistance genes. While further research is needed to assess the prevalence and diversity of antibiotic-resistant bacteria using advanced technologies such as metagenomics and transcriptomics, the scientists also said that the research results show the need for effective management of plastic waste and wastewater treatment to limit the spread of antibiotic resistance genes associated with microplastics.
The results are described in detail in the article “First evidence of microplastic-associated extended-spectrum beta-lactamase (ESBL)-producing bacteria in the Red River Delta, Vietnam”, published in the Journal of Hazardous Materials Letters.
Translated by Anh Vu from the Journal of Hazardous Materials Letters.
Source: https://doi.org/10.1016/j.hazl.2024.100129
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