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Abstract Microplastic contamination in marine organisms is a growing environmental issue with implications for seafood safety. Among marine organisms, shellfish are considered to be an important route of human exposure to microplastics because they filter a large volume of seawater while feeding and, thus, accumulate microplastics from seawater; furthermore, they are consumed whole, without gut removal. In this study, a market survey was carried out to understand microplastic contamination in domestic bivalves sold in fishery markets in three major cities of South Korea. Four popular bivalve species, oyster (Crassostrea gigas), mussel (Mytilus edulis), Manila clam (Tapes philippinarum) and scallop (Patinopecten yessoensis), were selected as monitoring species, which together account for 79–84% of total shellfish consumption in Korea. The mean concentration of microplastics in these four species was 0.15 ± 0.20 n/g and 0.97 ± 0.74 n/individual. Fragments and particles smaller than 300 μm were dominant shape and size, accounting for 76% and 65% of total microplastics, respectively. Polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyester were the major polymer types. Interestingly, differing polymer compositions were observed according to the culture methods and habitat characteristics of each species. PS was found in high proportions in oysters and mussels cultured in the upper layer of the water column, while the proportions decreased and those of polyester increased in Manila clams and scallops that were cultured in intertidal sediments or the middle and bottom layers of the water column. The annual dietary intake of microplastics by the Korean population via shellfish consumption was estimated as 212 n/person·year. Our results suggested that microplastic pollution is widespread in commercial bivalves and we recommend a systematic and integrative market-basket survey to clarify the current status of human exposure to microplastics. Graphical abstract Image 1 Highlights • Microplastic (MP) contamination in bivalves purchased from markets was studied. • MP contamination was widespread in market bivalves. • Shape and polymer type of MP were influenced by farming method of each species. • The dietary intake of MP by the Korean population via shellfish was estimated. • Seafood consumption can be a route of MP exposure for humans. Microplastic contamination in market bivalves from South Korea was investigated to understand human exposure to microplastics via seafood consumption. [ABSTRACT FROM AUTHOR]

Globally, sea turtles are at high risk of ingesting plastic. However, research on plastic ingestion by sea turtles in East Asia is scant, and no quantitative or qualitative investigation has been conducted in Korean waters. This study examined the plastic ingestion of sea turtles stranded, floating, or incidentally captured in Korean waters between 2012 and 2018. The quantity, shape, color, size, polymer type, and original usage of plastic debris (>1 mm) ingested by sea turtles were analyzed after being sorted from the gastrointestinal tracts of 34 turtles (21 loggerheads (Caretta caretta), 9 green turtles (Chelonia mydas), 2 leatherbacks (Dermochelys coriacea), and 2 olive ridleys (Lepidochelys olivacea)). The ingestion frequencies of greens, loggerheads, olive ridleys, and leatherbacks were 100%, 81%, 50%, and 50%, respectively. The mean amount of plastic ingested was 108 ± 253 mg/kg (38 ± 61 n/ind.). The ingested debris tended to be films and fibers (>80%), light in color (white and transparent; 65%), and light polymers (polyethylene, polypropylene, polypropylene [poly (ethylene:propylene)], expanded polystyrene; 93%). The original uses were identified for 187 pieces; single-use plastics (e.g., plastic bag and packaging) and fishing and aquaculture items (e.g., twine and net) were found to dominate. Green turtles (264 ± 433 mg/kg) ingested significantly higher amounts of plastic than loggerheads (72.8 ± 156 mg/kg). Green turtles ingested mostly fibers (51%), such as rope, twine, and net, while loggerheads ingested largely films (61%), such as plastic bags and packaging. Interspecies differences in quantities and shapes of ingested debris may be related to their distinct feeding habits and geographical range of movement. The present study demonstrates that sea turtles foraging in Korean waters are considerably affected by marine plastic debris, and indicates that proper waste management of single-use plastics and fishing gears is urgently needed to mitigate the damage that plastic debris causes to marine wildlife. [Display omitted] • Sea turtles inhabiting Korean waters are significantly affected by plastic debris. • Ingested plastics were mainly single-use and fishery items. • Plastic ingestion frequency and quantity were highest in green turtles. • Fibers and films were dominant in herbivore and carnivore turtles, respectively. • Sea turtles are key indicator species for assessing marine plastic pollution. [ABSTRACT FROM AUTHOR]

Microplastic pollution is emerging as a global environmental issue, and its potential for transferring hazardous chemicals to aquatic organisms is gaining attention. Studies have investigated the transfer of chemicals, mainly sorbed chemicals, through ingestion of microplastics by organisms, but limited information is available regarding chemical additives and uptake via the aqueous route through plastic leaching. In this study, we compared two bioaccumulation pathways of the additive hexabromocyclododecane (HBCD) by exposing mussels (Mytilus galloprovincialis) to two different sizes of expanded polystyrene (EPS): inedible size (4.2–5.5 mm) for leachate uptake and edible size (20–770 μm) for particle ingestion and leachate uptake. Over 10 days, the HBCD concentration increased significantly in mussels in the EPS exposure groups, indicating that EPS microplastic acts as a source of HBCD to mussels. The concentration and isomeric profiles of HBCD in mussels show that uptake through the aqueous phase is a more significant pathway for bioaccumulation of HBCD from EPS to mussels than particle ingestion. HBCD levels measured in EPS, leachate and exposed mussels from this study are environmentally relevant concentration. The fate and effects of chemical additives leached from plastic debris in ecosystem requires further investigation, as it may affect numerous environments and organisms through the aqueous phase. Image 1 • Additive HBCD uptake via EPS particle ingestion and EPS leachate were compared. • Mussels were exposed to edible and inedible sizes of EPS microplastics. • Aqueous leachate uptake is an important exposure route of EPS additives for mussels. • EPS microplastic acts as a source of plastic additives HBCD to mussel. Aqueous leachate uptake can be an important exposure route of microplastic additives for aquatic invertebrates. [ABSTRACT FROM AUTHOR]

This study assessed the ecological risk posed by microplastics in surface and subsurface seawaters in coastal, continental shelf, and deep-sea areas of South Korea. The target microplastics for risk assessment were specified as only non-spherical type microplastics in the size range 20–300 μm, because this type was predominantly observed in our study areas, and adverse biological effects have previously been reported. Exposure data for non-spherical microplastics were obtained from a previous study or were measured for microplastics of sizes down to 20 μm. A predicted no-effect concentration (PNEC) of 12 particles/L was derived by employing a species sensitivity distribution approach. Then the results were compared to the in situ observed concentrations at each site. The detected microplastic concentrations did not exceed the derived PNEC, i.e., the current pollution levels of fragment and fiber microplastics in the size range 20–300 μm would not pose a significant threat to the marine ecosystem in South Korea. However, predictions are that microplastic pollution will increase to 50-fold by 2100 at the current rates, and in this scenario, the microplastic concentration is expected to far exceed the derived PNEC values for marine ecosystems. It is therefore urgent to take precautionary actions to prevent a further increase in microplastic concentrations in these environments. Image 1 • Predicted no effect concentration (PNEC) for non-spherical microplastic was derived. • The microplastic concentrations in Korean marine water was lower than PNEC. • No ecological risk in Korean saltwater environments is suspected. • The microplastic concentration is predicted to well exceed PNEC value by 2100. • Actions to prevent a further increase in microplastic concentrations should be taken. Ecological risk assessment was conducted by matching size range and morphology of microplastics in both toxicity data and field monitoring data. [ABSTRACT FROM AUTHOR]

Bivalves are useful bioindicators of microplastic contamination in the marine environment for several reasons, such as extensive filter feeding activity, broad geographical distribution, and limited movement capability. This study conducted a nationwide monitoring of microplastic pollution along the Korean coasts using filter-feeding bivalves (including oyster, mussel, and Manila clam) as bioindicators to identify the national contamination level and characteristics of microplastics. Seawater sample was collected from the same sampling stations of oyster and mussel for comparison. Microplastics were widely distributed in both coastal bivalves and waters with mean concentrations of 0.33 ± 0.23 n/g (1.21 ± 0.68 n/individual) in oyster/mussel, 0.43 ± 0.32 n/g (2.19 ± 1.20 n/individual) in Manila clam, and 1400 ± 560 n/m3 in seawater. Despite the lack of significant relationship in the abundance of microplastics, their dominant features such as size, shape, color and polymer type were similar between bivalves and seawater. Fragments (69% for oyster/mussel, 72% for Manila clam, and 77% for seawater), particles smaller than 300 μm (96% for oyster/mussel, 83% for Manila clam, and 84% for seawater) and colorless (79% for oyster/mussel, 85% for Manila clam, 75% for seawater) were the dominant shape, size and color, respectively. The major polymer types were polypropylene, polyethylene, and polyester. The microplastic level in bivalves was relatively high in urbanized areas with a wide diversity of polymer types compared with those in non-urbanized areas, and the proportion of polystyrene in the Korean samples was abundant compared with other regions due to wide use of polystyrene products in Korea. Our result suggests that microplastic contamination is widespread in the Korean coastal environment, and bivalves can reflect the microplastic pollution characteristics of the surrounding waters where they live. Image 1 • Microplastic (MP) was widespread in bivalves and seawater from the Korea coasts. • Size, shape, and polymer type were similar between bivalves and nearby seawater. • Bivalves from urbanized areas exhibited high abundance and diversity of MP. A nationwide biomonitoring study was conducted to identify the national contamination level and characteristics of microplastics in Korea. [ABSTRACT FROM AUTHOR]

Background Antibiotics administered to farm animals have led to increasing prevalence of resistance genes in different microbiomes and environments. While antibiotic treatments help cure infectious diseases in farm animals, the possibility of spreading antibiotic resistance genes into the environment and human microbiomes raises significant concerns. Through long-term evolution, antibiotic resistance genes have mutated, thereby complicating the resistance problems. Results In this study, we performed deep sequencing of the gut microbiomes of 36 swine and 41 cattle in Korean farms, and metagenomic analysis to understand the diversity and prevalence of antibiotic resistance genes. We found that aminoglycoside, β-lactam, lincosamide, streptogramin, and tetracycline were the prevalent resistance determinants in both swine and cattle. Tetracycline resistance was abundant and prevalent in cattle and swine. Specifically, tetQ, tetW, tetO, tet32 , and tet44 were the 5 most abundant and prevalent tetracycline resistance genes. Their prevalence was almost 100% in swine and cattle. While tetQ was similarly abundant in both swine and cattle, tetW was more abundant in swine than in cattle. Aminoglycoside was the second highest abundant resistance determinant in swine, but not in cattle. In particular, ANT(6) and APH(3′′) were the dominant resistance gene families in swine. β-lactam was also an abundant resistance determinant in both swine and cattle. Cfx was the major contributing gene family conferring resistance against β-lactams. Conclusions Antibiotic resistome was more pervasive in swine than in cattle. Specifically, prevalent antibiotic resistance genes (prevalence >50%) were found more in swine than in cattle. Genomic investigation of specific resistance genes from the gut microbiomes of swine and cattle in this study should provide opportunities to better understand the exchange of antibiotic resistance genes in farm animals. [ABSTRACT FROM AUTHOR]

Polymyxins are the last-line antibiotics used to treat Gram-negative pathogens. Thus, the discovery and biochemical characterization of the resistance genes against polymyxins are urgently needed for diagnosis, treatment, and novel antibiotic design. Herein, we report novel polymyxin-resistance genes identified from sediment and seawater microbiome. Despite their low sequence identity against the known pmrE and pmrF , they show in vitro activities in UDP-glucose oxidation and l-Ara4N transfer to undecaprenyl phosphate, respectively, which occur as the part of lipid A modification that leads to polymyxin resistance. The expression of pmrE and pmrF also showed substantially high MICs in the presence of vanadate ions, indicating that they constitute polymyxin resistomes. IMPORTANCE Polymyxins are one of the last-resort antibiotics. Polymyxin resistance is a severe threat to combat multidrug-resistant pathogens. Thus, up-to-date identification and understanding of the related genes are crucial. Herein, we performed structure-guided sequence and activity analysis of five putative polymyxin-resistant metagenomes. Despite relatively low sequence identity to the previously reported polymyxin-resistance genes, at least four out of five discovered genes show reactivity essential for lipid A modification and polymyxin resistance, constituting antibiotic resistomes.

Antibiotics alter the gut microbiome and cause dysbiosis leading to antibiotic-resistant organisms. Different patterns of antibiotic administration cause a difference in bacterial composition and resistome in the human gut. We comprehensively investigated the association between the distribution of antibiotic resistance genes (ARGs), bacterial composition, and antibiotic treatments in patients with chronic obstructive pulmonary diseases (COPD) and Clostridioides difficile infections (CDI) who had chronic or acute intermittent use of antibiotics and compared them with healthy individuals. We analyzed the gut microbiomes of 61 healthy individuals, 16 patients with COPD, and 26 patients with CDI. The COPD patients were antibiotic-free before stool collection for a median of 40 days (Q1: 9.5; Q3: 60 days), while the CDI patients were antibiotic-free for 0 days (Q1: 0; Q3: 0.3). The intra-group beta diversity measured by the median Bray-Curtis index was the lowest for the healthy individuals (0.55), followed by the COPD (0.69) and CDI groups (0.72). The inter-group beta diversity was the highest among the healthy and CDI groups (median index = 0.89). The abundance of ARGs measured by the number of reads per kilobase per million reads (RPKM) was 684.2; 1,215.2; and 2,025.1 for the healthy, COPD, and CDI groups. It was negatively correlated with the alpha diversity of bacterial composition. For the prevalent ARG classes, healthy individuals had the lowest diversity and abundance of aminoglycoside, β-lactam, and macrolide-lincosamide-streptogramin (MLS) resistance genes, followed by the COPD and CDI groups. The abundances of Enterococcus and Escherichia species were positively correlated with ARG abundance and the days of antibiotic treatment, while Bifidobacterium and Ruminococcus showed negative correlations for the same. In addition, we analyzed the mobilome patterns of aminoglycoside and β-lactam resistance gene carriers using metagenomic sequencing data. In conclusion, the ARGs were significantly enhanced in the CDI and COPD groups than in healthy individuals. In particular, aminoglycoside and β-lactam resistance genes were more abundant in the CDI and COPD groups, but the dominant mobile genetic elements that enable the transfer of such genes showed similar prevalence patterns among the groups., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Cho, Kim, Pai and Rho.)

The routine therapeutic use of antibiotics has caused resistance genes to be disseminated across microbial populations. In particular, bacterial strains having antibiotic resistance genes are frequently observed in the human microbiome. Moreover, multidrug-resistant pathogens are now widely spread, threatening public health. Such genes are transferred and spread among bacteria even in different environments. Advances in high throughput sequencing technology and computational algorithms have accelerated investigation into antibiotic resistance genes of bacteria. Such studies have revealed that the antibiotic resistance genes are located close to the mobility-associated genes, which promotes their dissemination. An increasing level of information on genomic sequences of resistome should expedite research on drug-resistance in our body and environment, thereby contributing to the development of public health policy. In this review, the high prevalence of antibiotic resistance genes and their exchange in the human and environmental microbiome is discussed with respect to the genomic contents. The relationships among diverse resistomes, related bacterial species, and the antibiotics are reviewed. In addition, recent advances in bioinformatics approaches to investigate such relationships are discussed.