Monitoring of antimicrobial resistance genes in the spotted sea bass (Lateolabrax maculatus): Association with the microbiome and its environment in aquaculture ponds

Prevalence of opportunistic pathogens and anti-microbial resistance in urban aquaculture ponds

Bacterial antimicrobial resistance (AMR) has emerged as a significant concern worldwide. The microbial community profile and potential AMR level in aquaculture ponds are often undervalued and attract less attention than other aquatic environments. We used amplicon and metagenomic shotgun sequencing to study microbial communities and AMR in six freshwater polyculture ponds in rural and urban areas of Bangladesh. Amplicon sequencing revealed different community structures between rural and urban ponds, with urban ponds having a higher bacterial diversity and opportunistic pathogens including Streptococcus, Staphylococcus, and Corynebacterium. Despite proteobacterial dominance, Firmicutes was the most interactive in the community network, especially in the urban ponds. Metagenomes showed that drug resistance was the most common type of AMR found, while metal resistance was only observed in urban ponds. AMR and metal resistance genes were found mainly in beta and gamma-proteobacteria in urban ponds, while AMR was found primarily in alpha-proteobacteria in rural ponds. We identified potential pathogens with a high profile of AMR and metal resistance in urban aquaculture ponds. As these ponds provide a significant source of protein for humans, our results raise significant concerns for the environmental sustainability of this food source and the dissemination of AMR into the food chain.

The CRISPR/Cas system as an antimicrobial resistance strategy in aquatic ecosystems

With the growing population, demand for food has dramatically increased, and fisheries, including aquaculture, are expected to play an essential role in sustaining demand with adequate quantities of protein and essential vitamin supplements, employment generation, and GDP growth. Unfortunately, the incidence of emerging/re-emerging AMR pathogens annually occurs because of anthropogenic activities and the frequent use of antibiotics in aquaculture. These AMR pathogens include the WHO's top 6 prioritized ESKAPE pathogens (nosocomial pathogens: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.), extended-spectrum beta lactases (ESBLs) and carbapenemase-producing E. coli, which pose major challenges to the biomagnification of both nonnative and native antibiotic-resistant bacteria in capture and cultured fishes. Although implementing the rational use of antibiotics represents a promising mitigation measure, this approach is practically impossible due to the lack of awareness among farmers about the interplay between antimicrobial use and the emergence of antimicrobial resistance (AMR). Nevertheless, to eradicate these 'superbugs,' CRISPR/Cas (clustered regularly interspersed short palindromic repeats/CRISPR associate protein) has turned out to be a novel approach owing to its ability to perform precise site-directed targeting/knockdown/reversal of specific antimicrobial resistance genes in vitro and to distinguish AMR-resistant bacteria from a plethora of commensal aquatic bacteria. Along with highlighting the importance of virulent multidrug resistance genes in bacteria, this article aims to provide a holistic picture of CRISPR/Cas9-mediated genome editing for combating antimicrobial-resistant bacteria isolated from various aquaculture and marine systems, as well as insights into different types of CRISPR/Cas systems, delivery methods, and challenges associated with developing CRISPR/Cas9 antimicrobial agents.

Characteristics and driving factors of antibiotic resistance genes in aquaculture products from freshwater ponds in China Yangtze River Delta

Antibiotic resistance genes (ARGs) are widespread in aquaculture and pose a huge threat to aquaculture organisms and human health. In this study, occurrences and relative abundances of ARGs were analysed in the guts of products cultured in freshwater ponds in the Yangtze River Delta region in China. A total of 29 ARGs were found in the gut samples, with detection frequencies ranging from 4.8% to 81%, and the relative abundances (ARGs/16S rRNA) ranging from 10-7 to 1. In addition, the human dietary intake of ARGs via aquaculture products was assessed, where the daily intake of most ARGs via aquaculture products was higher than those via PM2.5 and drinking water, but lower than that via vegetables. The relative abundances of MGE (IS613, Tp614, tnpA and int1) were significantly correlated with those of multiple ARGs, indicating the horizontal gene transfer (HGT) of ARGs among gut microorganisms. Proteobacteria, Firmicutes and Actinobacteria were the dominated microbial communities found in the guts of aquaculture products. In addition, significant correlations were found between Cyanobacteria and int1, between Nitrospira and tetE, and between sul2 and aadA2, indicating potential same hosts of these genes. In addition, results from co-correlation indicated both HGT (dominated by MGEs) of ARGs and the enrichment of ARGs in bacteria. MGEs, mostly int1, were more effective than bacteria in increasing the ARG abundance. This study could provide a better understanding of the transmission of ARGs in the aquaculture environment and improve the quality of aquaculture products and the ecology.

Gender Impacted Gut Microbiota and Growth Performance in the Blotched Snakehead (Channa maculata)

The blotched snakehead Channa maculata is an important economical freshwater species in East Asia. However, there has been relatively little research conducted on the correlation between gender and gut microbes. In this study, 36 of 1000 blotched snakeheads were randomly selected for growth performance measurement and gut microbiota high-throughput sequencing. Results showed that microbial diversity, composition, and metabolic functions were altered by gender and growth performance except the microbial network. In our study, Proteobacteria were the most abundant phylum, with Fusobacteria showing enrichment in males and Bacteroidetes in females. Notably, phylum Deinococcus-Thermus was identified as a significant biomarker. The Cetobacterium was the most abundant genus-level taxon. Furthermore, gut microbes specializing in the production of gut-healthy substances, such as coenzymes and vitamins, were identified as biomarkers in the fast-growing group. Our investigation highlighted the impact of gender on the composition and abundance of gut microbial biomarkers in both males and females, thereby influencing differential growth performance through the modulation of specific metabolic functions.

Effects of cadmium exposure on gut microbiota and antibiotic resistance genes in Haliotis diversicolor abalone

Heavy metals in soil, water, and industrial production can affect the antibiotic resistance of bacteria. Antibiotic resistance in gut microbiota has been extensively researched. The effects of cadmium (Cd) was investigated on the gut microbiota and antibiotic resistance genes (ARGs) of Haliotis diversicolor, a commercially important abalone species. By exposing H. diversicolor to four concentrations of Cd (0 μg L-1 (control), 6.5 μg L-1 (low), 42.25 μg L-1 (medium), and 274.63 μg L-1 (high)) for 30 and 60 days, 16 types of ARG (aadA-01, aadA-02, cfr, dfrA1, ermB, floR, folA, mecA, sul2, tetB-01, tetC-01, tetD-01, tetG-01, tetM-02, tetQ, vanC-01), and 1213 genus and 27 phylum microbiomes were detected. ARGs can be resistant to aminoglycoside, beta-lactamase, macrolide-lincosamide-streptogramin B, multidrug, florfenicol, macrolide, sulfonamides, tetracyclines, and vancomycin. Cadmium exposure significantly alters the abundance of tetC-01, tetB-01, tetQ, sul2, and aadA-01. About 5% (61) of genus-level microorganisms were significantly affected by Cd exposure. Microbiota alpha and beta diversities in the 60-day 42.25 μg L-1 Cd treatment differed significantly from those in other treatments. In addition, 26 pathogens were detected, and two pathogens (Vibrio and Legionella) were significantly affected by Cd exposure. Significant correlations between pathogens and ARGs increased with increased Cd concentration after 60 days of Cd exposure. Cadmium exposure may cause gut microbiota disturbance in H. diversicolor and increase the likelihood of ARG transfer to pathogens, increasing potential ecological and economic risks.

Antibiotic resistance gene-free probiont administration to tilapia for growth performance and Streptococcus agalactiae resistance

Background and Aim

The rapid development of aquaculture as a major food sector is accompanied by challenges, including diseases that affect tilapia farming worldwide. One such infectious disease caused by Streptococcus agalactiae poses a serious threat to tilapia populations. Probiotics have emerged as a potentially safe preventive measure against S. agalactiae infection. However, antimicrobial resistance from antibiotic-resistant bacteria remains a concern because it can lead to the spread of resistant bacteria and serve as a reservoir of antibiotic-resistant genes in fishes and the surrounding environment. This study aimed to identify candidate probiotic bacteria capable of promoting tilapia growth, providing resistance to S. agalactiae infection, devoid of potential pathogenicity, and free from antibiotic resistance genes. Subsequently, the performance of these probiotic candidates in tilapia was evaluated.

Materials and Methods

Lactococcus garvieae, Priestia megaterium, Bacterium spp., Bacillus megaterium, Bacillus subtilis, and Bacillus pumilus were examined to assess their antibacterial properties, hemolytic patterns, and antibiotic resistance genes. We used the specific primers tetA, tetB, tetD, tetE, tetO, tetQ, ermB, and qnrS that were used for antibiotic resistance gene detection. In vivo probiotic efficacy was evaluated by administering probiotic candidates in tilapia feed at a concentration of 1 × 106 colonies/mL/50 g of feed over a 60-day maintenance period. Resistance to S. agalactiae infection was observed for 14 days after the challenge test.

Results

Lactococcus garvieae, P. megaterium, and Bacterium spp. were identified as promising probiotic candidates among the bacterial isolates. On the other hand, B. megaterium, B. subtilis, and B. pumilus carried resistance genes and exhibited a β hemolytic pattern, rendering them unsuitable as probiotic candidates. The selected probiotic candidates (L. garvieae, P. megaterium, and Bacterium spp.) demonstrated the potential to enhance tilapia growth, exhibited no pathogenic tendencies, and were free from antibiotic resistance genes. Supplementation with L. garvieae and Bacterium spp. enhanced tilapia resistance to S. agalactiae infection, whereas P. megaterium supplementation showed an insignificant survival rate compared with controls after the challenge test period.

Conclusion

Probiotics, particularly L. garvieae, P. megaterium, and Bacterium spp., enhance growth and resistance against S. agalactiae infection, without harboring antibiotic resistance genes. Selecting probiotic candidates based on antibiotic resistance genes is essential to ensure the safety of fish, the environment, and human health.

Exposure to cadmium induced gut antibiotic resistance genes (ARGs) and microbiota alternations of Babylonia areolata

Cadmium (Cd) is widely distributed in aquatic environments and has multiple adverse effects on aquatic organisms such as the ivory shell (Babylonia areolata). However, its effects on antibiotic resistance genes (ARGs) and gut microbiota of B. areolata remain unclear. In this study, we explored the effects of different concentrations (0, 0.03, 0.18 and 1.08 mg/L) of Cd on intestinal microbial communities and ARGs in B. areolata through 16S rRNA gene sequencing and high-throughput quantitative PCR. The results showed that the structure and diversity of ARGs and microbiota in B. areolata gut were altered upon Cd exposure. Tetracycline, Vancomycin and Macrolide-Lincosamide-Streptogramin B (MLSB) resistance genes were identified as the major ARGs in B. areolata gut. The absolute abundance and alpha diversity of ARGs in B. areolata gut increased with the rise of cadmium concentration. The microbial communities at genus level were enriched in the low and medium Cd concentration groups, while decreased in the high Cd concentration group compared to the control groups. In addition, the influence of microbiota on the ARG profile was more significant than that of Cd concentration and MGEs in B. areolata gut. Null model analysis demonstrated that stochastic processes dominated ARG assembly in the Cd-exposed groups and were enhanced with the increasing Cd concentrations. Four opportunistic bacterial pathogens (Bacteroides, Legionella, Acinetobacter and Escherichia) detected in B. areolata gut maybe the potential hosts of ARGs. Our findings provide references for the hazards assessment of environmental Cd exposure of gut microbiome in aquatic animals.

Meta-analysis addressing the characterization and risk identification of antibiotics and antibiotic resistance genes in global groundwater

Antimicrobial resistance (AMR) is one of the significant global issues to public health. Compared to other aquatic environments, research on AMR in groundwater is scarce. In the study, a meta-analysis was conducted to explore the characteristics and risks of antibiotics and antibiotic resistance genes (ARGs) in global groundwater, using a data set of antibiotic concentrations collected from publications during 2000-2021 and a large-scale metagenomes of groundwater samples (n = 330). The ecotoxicological risks of antibiotics in the global groundwater were evaluated using mixture risk quotient with concentration addition model to consider the synergistic effects of multiple antibiotics. Bioinformatic annotations identified 1413 ARGs belonging to 37 ARG types in the global groundwater, dominated by rifamycin, polyketide, and quinolone resistance genes and including some emerging ARGs such as mcr-family and carbapenem genes. Relatively, the level of ARGs in the groundwater from spring was significantly higher (ANOVA, p < 0.01) than those from the riparian zone, sand and deep aquifer. Similarly, metal resistance genes (MRGs) were prevalent in the global groundwater, and network analysis suggested the MRGs presented non-random co-occurrence with the ARGs in such environments. Taxonomic annotations showed Proteobacteria, Actinobacteria, Eukaryota, Acidobacteria and Thaumarchaeota were the dominant phylum in the groundwater, and the microbial community largely shaped profile of ARGs in the environment. Notably, the ARGs presented co-occurrence with mobile genetic elements, virulence factors and human bacterial pathogens, indicating potential dissemination risk of ARGs in the groundwater. Furthermore, an omics-based approach was used for health risk assessment of antibiotic resistome and screened out 152 risk ARGs in the global groundwater. Comparatively, spring and cold creek presented higher risk index, which deserves more attention to ensure the safety of water supply.

Antimicrobial susceptibility test and antimicrobial resistance gene detection of extracellular enzyme bacteria isolated from tilapia (Oreochromis niloticus) for probiotic candidates

Background and Aim: Antimicrobial resistance (AMR) is a global problem that can increase mortality and morbidity rates and adversely affect health. Therefore, AMR control must be carried out in various sectors, including the fisheries sector, using probiotics. Bacteria can become resistant to antibiotics, including bacteria used for probiotics. This study aimed to isolate bacteria as potential producers of extracellular enzymes, phenotypic characterization, and antibiotic-resistant gene patterns. Materials and Methods: In this study, 459 bacterial isolates were isolated from the stomach of tilapia in Indonesia. Tilapia was obtained from Sukabumi, Ciamis, Serang, Banjarnegara, Jayapura, Sorong, Manokwari Selatan, Takalar, Lampung, Batam, and Mandiangin. Enzymatic bacteria were identified. An antimicrobial susceptibility test was conducted by agar disk diffusion, and genotypic detection of encoding genes was performed using a molecular method. Results: This study obtained 137 isolates (29.84%) that can produce extracellular enzymes. The highest number of E-sensitive isolates was found, including 130 isolates (94.89%). Six isolates (6/137) can produce four enzymes (amylase, protease, cellulose, and lipase), and they were sensitive to antibiotics. A total of 99 isolates can produce extracellular enzymes, and they were sensitive to antibiotics. Such isolates serve as a consortium of probiotic candidates. The isolates that are resistant to oxytetracycline (OT), erythromycin (E), tetracycline (TE), and enrofloxacin (ENR) included 15 isolates (10.95%), seven isolates (5.11%), three isolates (2.19%), and one isolate (0.73%), respectively. In addition, four isolates (2.92%) were detected as multidrug-resistant. The tet(A) gene obtained the highest result of detection of resistance genes in isolates that were intermediate and resistant to TE and OT. Isolates that serve as ENR intermediates have a high qnr(S) resistance gene. Conclusion: The data in this study provide the latest update that bacteria can serve as a consortium of potential probiotics with antibiotic-resistant genes for the treatment of fish. Bacteria that are intermediate to antibiotics may contain resistance genes. The results of this study will improve the policy of probiotic standards in Indonesia.

Anthropogenic impacts on antibiotic resistance genes and their hosts from pristine to urban river using metagenomic and binning approaches

Driven by anthropogenic pressure, Antibiotic resistance genes (ARGs) could transfer from the environmental resistome into human commensals or even pathogens. The transport of ARGs through aquatic ecosystems is crucial and has attracted attention. Here, we employed metagenomic and binning to compare ARGs profiles, their co-occurrence with metal resistance genes (MRGs) and mobile genetic elements (MGEs), and their hosts between pristine and anthropogenic influenced rivers and explore the ecological mechanisms underlying the dissemination of ARGs induced by anthropogenic activities. The significantly increased relative abundance of macrolide-lincosamide-streptogramins, vancomycin, β-lactam and sulfonamide resistance genes along the environmental gradient from pristine to polluted sediments implied that anthropogenic impact aided the emergence and dissemination of certain ARGs. At the lower reach of the Ba River, the higher ratios for contigs carrying more than one ARG suggested that anthropogenic pollution favored the co-occurrence of multiple ARGs. Anthropogenic pressures also increased the relative abundance of advantaged hosts, including Chloroflexi, Firmicutes and Euryarchaeota. At the lower reach of Ba River, Romboutsia timonensis carrying multiple ARGs and ICEs were successfully recovered, posing a serious threat to human health by affecting the metabolism of gut microbiomes. And Methanothrix soehngenii affiliated to archaea carrying multiple ARGs, MRGs and ICEs were also recovered from the lower Ba River. The partial least squares path modeling revealed that MGEs were the most predominant factors inducing the ARG profiles, and the antibiotic resistance could be enriched by co-transfer with MRGs. Furthermore, environmental factors could impact the ARG profiles indirectly by first influencing the ARGs' hosts.

Interaction of Microbiota between Fish and the Environment of an In-Pond Raceway System in a Lake

Due to its ability to collect and remove aquaculture waste, an in-pond raceway system (IPRS) has been used to decrease the uncontrolled waste discharge in the traditional cage aquaculture method in large water bodies. However, when applied to large water bodies, its environmental performance is still lacking. This study focused on analyzing the microbial characteristics and the interaction between largemouth bass (gill and gut) microbiota and the environment (water and sediment) microbiota of an IPRS. Further, it revealed the primary relationship from the perspective of microbiota in the IPRS. The results show that (1) the alpha diversity of microbiota in the water is significantly lower than that of fish and sediment. The relationship between water microbiota and fish microbiota is limited. (2) The water microbiota inside and outside the tank showed high similarity and were not significantly affected by environmental factors. (3) The SourceTrack analysis showed that fish microbiota is one of the primary sources of sediment microbiota, and more than 15% of the sediment microbiota come from fish. Microbes such as Faecalibacterium, Escherichia-Shigella, and Bacteroides can significantly enrich the sediment. Our study revealed the characteristics and preliminary interaction of fish and environmental microbiota in the IPRS. It provided a reference for evaluating microbial health status in the application of IPRS in large water bodies’ aquaculture.

Migration of antibiotic resistance genes and evolution of flora structure in the Xenopus tropicalis intestinal tract with combined exposure to roxithromycin and oxytetracycline

The intestinal flora is one of the most important environments for antibiotic resistance development, owing to its diverse mix of bacteria. An excellent medicine model organism, Xenopus tropicalis, was selected to investigate the spread of antibiotic resistance genes (ARGs) in the intestinal bacterial community with single or combined exposure to roxithromycin (ROX) and oxytetracycline (OTC). Seventeen resistance genes (tetA, tetB, tetE, tetM, tetO, tetS, tetX, ermF, msrA, mefA, ereA, ereB, mphA, mphB, intI1, intI2, intI3) were detected in the intestines of Xenopus tropicalis living in three testing tanks (ROX tanks, OTC tanks, ROX + OTC tanks) and a blank tank for 20 days. The results showed that the relative abundance of total ARGs increased obviously in the tank with single stress but decreased in the tank with combined stress, and the genes encoding the macrolide antibiotic efflux pump (msrA), phosphatase (mphB) and integron (intI2, intI3) were the most sensitive. With the aid of AFM scanning, DNA was found to be scattered short chain in the blank, became extended or curled and then compacted with the stress from a single antibiotic, and was compacted and then fragmented with combined stress, which might be the reason for the variation of the abundance of ARGs with stress. The ratio of Firmicutes/Bacteroides related to diseases was increased by ROX and OTC. The very significant correlation between intI2 and intI3 with tetS (p ≤ 0.001) hinted at a high risk of ARG transmission in the intestines. Collectively, our results suggested that the relative abundance of intestinal ARGs could be changed depending on the intestinal microbiome and DNA structures upon exposure to antibiotics at environmental concentrations.

Antibiotics, antibiotic resistance genes and microbial community in grouper mariculture

Increasing use of feed and medicine in mariculture could cause negative environmental impacts such as habitat modification, microbial disease development and antibiotic resistance. Here we investigated contamination of antibiotics and antibiotic resistance genes (ARGs), and composition of microbial community in grouper mariculture systems in Hainan province, China. Results showed detection of various antibiotic residues with the dominance of fluoroquinolones and tetracyclines in the six grouper cultivation systems. The concentrations of the detected antibiotics in the grouper mariculture water were significantly higher than those in the original seawater. Some of the detected antibiotics such as enrofloxacin, ciprofloxacin, ofloxacin, oxytetracycline and erythromycin in the mariculture water and/or sediment would pose high resistance selection risks. Sulfonamides resistance genes sul1 and sul2 were found to be predominant in water and sediment, while tetracycline resistance genes were prevalent in fish gill and gut. The dominant bacterial phyla in water and sediments were Bacteroides, Actinomycetes, and Proteobacteria, while the dominant ones in fish gill and gut were the Proteobacteria. Genera of Vibrio and Mycobacterium in the core microbiota were important zoonotic pathogens, and there was a significant positive correlation between Vibrio and ARGs. Phyla of Proteobacteria, Actinomyces, and Cyanobacteria were positively correlated to ARGs, indicating that these microorganisms are potential hosts of ARGs. The putative functions of microbiome related to antibiotic resistance and human diseases were significantly higher in fish than in the mariculture environment. This study suggests that mariculture system is a reservoir of ARGs, and the use of antibiotics in mariculture could induce the increase of antibiotic resistance and the prevalence of opportunistic pathogens.

Is rice-crayfish co-culture a better aquaculture model: From the perspective of antibiotic resistome profiles

Aquaculture ecosystem is a hot-spot for antibiotic resistance genes (ARGs). Rice-crayfish co-culture was considered an eco-friendly aquaculture model and has been widely adopted in China. However, it is unclear whether rice-crayfish co-culture is one of the most eco-friendly models from the perspective of antibiotic resistance profiles. In this study, we evaluated the eco-friendliness of rice-crayfish co-culture, and compared this model with other aquaculture models, from the perspectives of antibiotics and ARG patterns, based on multi-omics and antibiotic profiles. Results showed that the nutrient levels, antibiotic concentrations, dominant microbial genera and ARG patterns in the rice-crayfish co-culture model were profoundly different from the other three aquaculture models (crab only aquaculture model, crayfish only aquaculture model, and crab-crayfish co-culture models). Specifically, the rice-crayfish co-culture model has significantly lower diversity of ARGs and lower potential risks of ARGs when compared to the other aquaculture models. Nutrient and antibiotic concentrations were the important environmental factors for shaping ARG patterns, but compared with environmental factors, the effects of mobile genes and bacteria community on the proliferation and transmission of ARGs were stronger. This study has deepened our understanding of ARGs in freshwater aquaculture ecosystem, and suggested that rice-crayfish co-culture model is a relatively eco-friendly aquaculture model when compared with the other aquaculture models.

Investigating the Effect of an Oxytetracycline Treatment on the Gut Microbiome and Antimicrobial Resistance Gene Dynamics in Nile Tilapia (Oreochromis niloticus)

Antibiotics play a vital role in aquaculture where they are commonly used to treat bacterial diseases. However, the impact of antibiotic treatment on the gut microbiome and the development of antimicrobial resistance in Nile tilapia (Oreochromis niloticus) over time remains to be fully understood. In this study, fish were fed a single treatment of oxytetracycline (100 mg/kg/day) for eight days, followed by a 14-day withdrawal period. Changes in the distal gut microbiome were measured using 16S rRNA sequencing. In addition, the abundance of antimicrobial resistance genes was quantified using real-time qPCR methods. Overall, the gut microbiome community diversity and structure of Nile tilapia was resilient to oxytetracycline treatment. However, antibiotic treatment was associated with an enrichment in Plesiomonas, accompanied by a decline in other bacteria taxa. Oxytetracycline treatment increased the proportion of tetA in the distal gut of fish and tank biofilms of the treated group. Furthermore, the abundance of tetA along with other tetracycline resistance genes was strongly correlated with a number of microbiome members, including Plesiomonas. The findings from this study demonstrate that antibiotic treatment can exert selective pressures on the gut microbiome of fish in favour of resistant populations, which may have long-term impacts on fish health.