Longitudinal study on the effects of growth-promoting and therapeutic antibiotics on the dynamics of chicken cloacal and litter microbiomes and resistomes

Metagenomic insights into microbial diversity and potential pathogenic transmission in poultry farm environments of Bangladesh

The microbiome plays a critical role in poultry health and productivity, influencing growth, immunity, and the overall farm ecosystem. This study investigated microbial diversity, antibiotic resistance pathways, and functional potential across various components of poultry ecosystems-cloacal swabs, droppings, feed, hand swabs, soil, and water-in different districts of Bangladesh. Using 16S rRNA gene amplicon sequencing, we identified 2,745 Operational Taxonomic Units (OTUs) and analyzed microbial richness, community structure, and functional pathways. Alpha diversity metrics revealed that droppings exhibited the highest microbial richness (726 OTUs in Noakhali), while feed samples showed the lowest diversity (211 OTUs). Beta diversity analysis indicated significant differences in microbial composition across sample sources, with PERMANOVA confirming that sample origin accounted for 51.45% of the variability (p < 0.001). Proteobacteria dominated the microbial communities (48.36%), followed by Firmicutes (19.83%) and Cyanobacteria (12.02%). Key genera of concern, such as Enterobacter (26.62% in hand swabs), Acinetobacter (30.87% in cloacal swabs), and Shigella (22.89% in cloacal swabs), were identified, highlighting potential contamination and zoonotic risks. Conversely, beneficial genera like Lactobacillus (36.89% in feed) and Enterococcus (10.78% in droppings) were prevalent, suggesting roles in gut health and nutrient cycling. Functional pathway analysis (KEGG) revealed that carbohydrate and amino acid metabolism were highly active in droppings and feed, reflecting nutrient utilization. Antimicrobial resistance (AMR) pathways, such as 23S rRNA-methyltransferase and multidrug efflux pumps, were widespread, with pathogenic genera (Enterobacter, Acinetobacter, Shigella, Pseudomonas) showing strong positive correlations with AMR pathways. These findings underscore the influence of environmental factors on microbial diversity and functional potential in poultry farming. The study highlights the need for improved management practices and biosecurity measures to mitigate risks associated with microbial pathogens and antimicrobial resistance, ultimately supporting healthier and more sustainable poultry production in Bangladesh.

Unveiling soil-borne antibiotic resistome and their associated risks: A comparative study of antibiotic and non-antibiotic pharmaceutical factories

Antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) are extensively documented within antibiotic pharmaceutical factories. Notably, non-antibiotic pharmaceuticals also represent a significant portion of the pharmaceuticals market. However, the comparative analyses of soil-borne ARG profiles and associated risks in different categories of pharmaceutical factories remain limited. This study conducted metagenomic sequencing on soil samples collected from both antibiotic and non-antibiotic pharmaceutical factories, alongside isolated ARB from soil, wastewater, groundwater, and air. Our results indicated the significant discrepancies in soil-borne ARG profiles, comprising abundance, diversity, and composition, in different categories of pharmaceutical factories (P < 0.05), which mainly driven by antibiotic residues. Significantly, bacterial pathogens were the important soil-borne ARG hosts, potentially posing risks to human health. In addition, the full-length nucleotide sequences of sul1, tetA, and TEM-1 were similar among soil, wastewater, groundwater, and air, suggesting the cross-media ARG dissemination within pharmaceutical settings. Through macrophage and Galleria mellonella infection models, the isolated antibiotic-resistant Escherichia coli strains possessed relatively high virulence. Overall, the findings provide valuable insights into the discrepancies in soil-borne ARG profiles and associated risks across different types of pharmaceutical factories, offering critical data for the targeted prevention and control of soil-borne ARG contamination in pharmaceutical production settings.

Whole genome sequencing revealed high occurrence of antimicrobial resistance genes in bacteria isolated from poultry manure

BACKGROUND

Global demand for food has driven expansion and intensification of livestock production, particularly in developing nations where antibiotic use is often routine. Waste from poultry production, including manure, is commonly utilized as fertilizers in agroecosystems, risking environmental contamination with potentially zoonotic bacteria and antimicrobial resistance genes (ARGs).

METHODS

Here, 33 bacterial isolates were recovered from broiler (n = 17) and layer (n = 16) chicken manure by aerobic culture using Luria Bertani agar. Antimicrobial susceptibility testing (AST) was performed using disc diffusion method. MALDI-ToF and 16S rRNA sequencing were used to identify and compare a subset of antibiotic-resistant isolates (n = 13). Comparison of whole genome sequence assemblies and phenotypic assays were used to assess capacity for biofilm formation, heavy metal tolerance and virulence.

RESULTS

AST by disc diffusion revealed all isolates were resistant to a minimum of three antibiotics, with resistance to ampicillin, co-trimoxazole, fluoroquinolones, tetracyclines, streptomycin, rifampicin and/or chloramphenicol detected. Stutzerimonas sp. and Acinetobacter sp. were the common genera observed in this study. Genome sequencing of each selected isolate revealed carriage of multiple ARGs capable of conferring resistance to many antimicrobials commonly employed in poultry production and human medicine, including tetracyclines, quinolones, macrolides, sulfonamide and cephalosporins.

CONCLUSIONS

The high occurrence of ARGs in studied bacterial isolates confirms that poultry manure could act as a source of genetic material that could be transferred to commensal microbiota and opportunistic pathogens of humans. Understanding the complex resistome interplay between humans, animals, and the environment requires a One Health approach, with implications for agricultural settings and public health.

Dietary addition of compound organic acids improves the growth performance, carcass trait, and body health of broilers

Introduction

The poultry industry constantly seeks strategies to enhance broiler growth performance and overall health. Organic acidifiers, including L-lactic acid, L-malic acid, and acetic acid, have gained attention as potential feed additives to improve animal production by modulating gut health, enhancing nutrient absorption, and supporting immune function. Despite their promising effects in other animal species, the impact of this novel compound organic acidifier on broiler performance, metabolism, and immune response has not been fully elucidated. This study aims to evaluate the effects of this compound acidifier on growth performance, serum lipid profile, antioxidant status, and immune parameters in broilers, providing insights into its potential benefits as a dietary supplement for broiler health and productivity.

Methods

A total of 240 broilers were randomly divided into four groups: a control group and three treatment groups receiving 0.25%, 0.5%, or 1.0% acidifier, with six replicates of ten birds each. Over a 6-week period, various parameters were measured, including serum triglycerides, high-density lipoproteins, lysozyme, immunoglobulins (IgA, IgM), superoxide dismutase (SOD) activity, IL-2, TNF-α, and gene expressions related to lipid metabolism.

Results

Over a 6-week period, the acidifier decreased serum triglycerides and high-density lipoproteins while also enhancing growth performance. Additionally, it raised the serum levels of lysozyme, IgA, IgM, and the SOD. Additionally, IL-2 and TNF-α concentrations in the jejunum mucosa decreased. The acidifier upregulated PPARα, AMPK, FABP1 and MTTP expressions, and downregulated APOB100. Overall, the acidifier effectively improved broiler growth performance during the early development phase primarily by enhancing hepatic lipid metabolism, antioxidant capacity, and immune function.

Conclusion

These results suggest that the acidifier may accelerate liver lipid metabolism in broilers by modulating the gene expression profiles involved in lipid metabolism.

Occurrence of "under-the-radar" antibiotic resistance in anthropogenically affected produce

With global climate change, treated-wastewater irrigation and manure amendment are becoming increasingly important in sustainable agriculture in water- and nutrient-stressed regions. Yet, these practices can potentially disseminate pathogens and antimicrobial resistance determinants to crops, resulting in serious health risks to humans through the food chain. Previous studies demonstrated that pathogen and antimicrobial resistance indicators from wastewater and manure survive poorly in the environment, suggesting that ecological barriers prevent their dissemination. However, we recently found that these elements can persist below detection levels in low quality treated wastewater-irrigated soil, and potentially proliferate under favorable conditions. This "under-the-radar" phenomenon was further investigated here, in treated wastewater-irrigated and poultry litter-amended lettuce plants, using an enrichment platform that resembles gut conditions, and an analytical approach that combined molecular and cultivation-based techniques. Enrichment uncovered clinically relevant multidrug-resistant pathogen indicators and a myriad of antibiotic resistance genes in the litter amended and treated wastewater-irrigated lettuce that were not detected by direct analyses, or in the enriched freshwater irrigated samples. Selected resistant E. coli isolates were capable of horizontally transferring plasmids carrying multiple resistance genes to a susceptible strain. Overall, our study underlines the hidden risks of under-the-radar pathogen and antimicrobial resistance determinants in anthropogenically affected agroenvironments, providing a platform to improve quantitative microbial risk assessment models in the future.

Comparative metagenomics reveals limited differences in antimicrobial resistance gene abundance across conventional and natural livestock production systems

The livestock industry has been a source of concern in terms of antimicrobial resistance (AMR) development and spread, especially from a One Health perspective. Raising livestock without antimicrobials, so called natural (NAT) production, is an increasingly popular practice. This study used metagenomics to compare this practice to conventional (CONV) antimicrobial use (AMU) on the microbiome and resistome in the feces of beef cattle and swine and the cecal contents of broiler chickens. In cattle, Bacteroidetes, Euryarchaeota, and Spirochaetes were more abundant (q < 0.01) in CONV than NAT systems, with no differences (q > 0.05) in bacterial profiles in either swine or chickens. Classes of antimicrobial resistant genes (ARG) were not impacted regardless of AMU in any of the livestock species. However, many tetracycline resistance genes were more abundant in CONV as compared to NAT swine (q < 0.05), but this difference was not observed in cattle or chickens. This study confirmed that elimination of AMU does not necessarily result in an immediate decline in the abundance or diversity of ARGs within a single livestock production cycle.

Antimicrobial resistance in plant endophytes associated with poultry-manure application revealed by selective culture and whole genome sequencing

Poultry manure is widely used as organic fertilizer in agriculture during the cultivation of crops, but the persistent high-level use of antibiotics in poultry production has raised concerns about the selection for reservoirs of antimicrobial resistance genes (ARGs). Previous studies have shown that the addition of poultry manure can increase the abundance of genes associated with resistance to tetracyclines, aminoglycosides, fluoroquinolones, sulfonamides, bacitracin, chloramphenicol, and macrolide-lincosamide-streptogramin in soil and plants. Understanding the microbial populations that harbor these ARGs is important to identify microorganisms that could enter the human food chain. Here, we test the hypothesis that environmental exposure to poultry manure increases the occurrence of antimicrobial resistance (AMR) in plant endophytes using selective culture, phenotypic Antibiotic Susceptibility Testing (AST), phylogenetic analysis, and whole genome sequencing (WGS). Endophytes from poultry manure treated Sorghum bicolor (L.) Moench plant root and stem samples showed increased phenotypic and genotypic resistance against multiple antibiotics compared to untreated controls. Comparison of AMR phenotype-to-genotype relationships highlighted the detection of multi-drug resistant (MDR) plant endophytes, demonstrating the value of genomic surveillance for emerging drug-resistant pathogens. The increased occurrence of ARGs in poultry manure-exposed endophytes highlights the need for responsible antibiotic use in poultry and animal farming to reduce contamination of ecological niches and transgression into endophytic plant microbiome compartments. It also emphasizes the requirement for proper manure management practices and vigilance in monitoring and surveillance efforts to tackle the growing problem of antibiotic resistance and preserve the efficacy of antibiotics for human and veterinary medicine.

Avian Pathogenic Escherichia coli: An Overview of Infection Biology, Antimicrobial Resistance and Vaccination

Avian Pathogenic Escherichia coli (APEC) is an extraintestinal pathotype of E. coli that leads to a range of clinical manifestations, including respiratory, systemic and reproductive infections of chickens in both egg and meat production. Unlike most E. coli pathotypes, APEC is not defined by specific virulence genes but rather is a collection of several distinct genotypes that can act as both primary and secondary pathogens leading to colibacillosis. Recent measures to reduce antimicrobials both as growth promoters and as flock-level therapeutics are considered to have led to increased numbers of animals affected. Nevertheless, antimicrobial resistance is a considerable problem in APEC, with resistance to third and fourth-generation cephalosporins via extended-spectrum beta-lactamases (ESBLs), fluoroquinolones and colistin seen as a particular concern. The need to control APEC without antimicrobial use at the flock level has seen an increased focus on vaccination. Currently, a few commercial vaccines are already available, and a range of approaches are being applied to develop new vaccines, and other controls, such as bacteriophage or probiotics, are attracting interest. The lack of a single defined APEC genotype presents challenges to these approaches.

Large-Scale Field Trials of an Eimeria Vaccine Induce Positive Effects on the Production Index of Broilers

Live coccidiosis vaccines have mainly been used to reduce Eimeria species infection, which is considered the most economically important disease in the poultry industry. Evaluation data on vaccine effectiveness through large-scale field experiments are lacking, especially in broilers. Thus, the effectiveness of a commercial coccidiosis vaccine was evaluated in approximately 900,000 chicks reared on three open-broiler farms where coccidiosis is prevalent. The vaccine's effectiveness after vaccination of 1-day-old chicks was monitored using three parameters (lesion score, fecal oocyst shedding, and production index, PI) in nine trials performed three times on each farm. Lesion scores were confirmed in three different areas of the intestine because the vaccine contained four Eimeria species. The average lesion scores were 0.36 to 0.64 in the duodenal region, 0.30 to 0.39 in the jejuno-ileal region, and 0.18 to 0.39 in the cecal region. The average fecal oocyst shedding rate ranged from 19,766 to 100,100 oocysts per gram, showing large variations depending on farms and buildings within the farm. Compared with the PI of the previous 9-10 trials on each farm, the PI increased by 2.45 to 23.55. Because of the potential for perturbation of the fecal microbiota by live coccidiosis vaccines, the fecal microbiota was investigated using 16S rRNA microbial profiling. Although the β-diversity was significantly different in distribution and relative abundance among farms (PERMANOVA, pseudo-F = 4.863, p = 0.009), a Kyoto Encyclopedia of Genes and Genomes pathway analysis found no significant bacterial invasion of the epithelial cell pathway across farms. This large-scale field trial of a live Eimeria vaccine indicates that coccidiosis vaccines can have meaningful effects on the poultry industry and could be used as an alternative to the prophylactic use of anticoccidial drugs under field conditions.

Accessory genes define species-specific routes to antibiotic resistance

A deeper understanding of the relationship between the antimicrobial resistance (AMR) gene carriage and phenotype is necessary to develop effective response strategies against this global burden. AMR phenotype is often a result of multi-gene interactions; therefore, we need approaches that go beyond current simple AMR gene identification tools. Machine-learning (ML) methods may meet this challenge and allow the development of rapid computational approaches for AMR phenotype classification. To examine this, we applied multiple ML techniques to 16,950 bacterial genomes across 28 genera, with corresponding MICs for 23 antibiotics with the aim of training models to accurately determine the AMR phenotype from sequenced genomes. This resulted in a >1.5-fold increase in AMR phenotype prediction accuracy over AMR gene identification alone. Furthermore, we revealed 528 unique (often species-specific) genomic routes to antibiotic resistance, including genes not previously linked to the AMR phenotype. Our study demonstrates the utility of ML in predicting AMR phenotypes across diverse clinically relevant organisms and antibiotics. This research proposes a rapid computational method to support laboratory-based identification of the AMR phenotype in pathogens.

The multi-kingdom microbiome catalog of the chicken gastrointestinal tract

Chicken is an important food animal worldwide and plays an important role in human life by providing meat and eggs. Despite recent significant advances in gut microbiome studies, a comprehensive study of chicken gut bacterial, archaeal, and viral genomes remains unavailable. In this study, we constructed a chicken multi-kingdom microbiome catalog (CMKMC), including 18,201 bacterial, 225 archaeal, and 33,411 viral genomes, and annotated over 6,076,006 protein-coding genes by integrating 135 chicken gut metagenomes and publicly available metagenome-assembled genomes (MAGs) from ten countries. We found that 812 and 240 MAGs in our dataset were putative novel species and genera, respectively, far beyond what was previously reported. The newly unclassified MAGs were predominant in Phyla Firmicutes_A (n = 263), followed by Firmicutes (n = 126), Bacteroidota (n = 121), and Proteobacteria (n = 87). Most of the classified species-level viral operational taxonomic units belong to Caudovirales. Approximately, 63.24 % of chicken gut viromes are predicted to infect two or more hosts, including complete circular viruses. Moreover, we found that diverse auxiliary metabolic genes and antibiotic resistance genes were carried by viruses. Together, our CMKMC provides the largest integrated MAGs and viral genomes from the chicken gut to date, functional insights into the chicken gastrointestinal tract microbiota, and paves the way for microbial interventions for better chicken health and productivity.

The Complex Interplay Between Antibiotic Resistance and Pharmaceutical and Personal Care Products in the Environment

Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are important environmental contaminants. Nonetheless, what drives the evolution, spread, and transmission of antibiotic resistance dissemination is still poorly understood. The abundance of ARB and ARGs is often elevated in human-impacted areas, especially in environments receiving fecal wastes, or in the presence of complex mixtures of chemical contaminants, such as pharmaceuticals and personal care products. Self-replication, mutation, horizontal gene transfer, and adaptation to different environmental conditions contribute to the persistence and proliferation of ARB in habitats under strong anthropogenic influence. Our review discusses the interplay between chemical contaminants and ARB and their respective genes, specifically in reference to co-occurrence, potential biostimulation, and selective pressure effects, and gives an overview of mitigation by existing man-made and natural barriers. Evidence and strategies to improve the assessment of human health risks due to environmental antibiotic resistance are also discussed. Environ Toxicol Chem 2024;43:637-652. © 2022 SETAC.

Effects of Neolamarckia cadamba leaves extract on microbial community and antibiotic resistance genes in cecal contents and feces of broilers challenged with lipopolysaccharides

The effects of Neolamarckia cadamba leaves extract (NCLE), with effective ingredients of flavonoids, on antibiotic resistance genes (ARGs) and relevant microorganisms in cecal contents and feces of broilers treated with or without lipopolysaccharide stimulation (LPS) were investigated. LPS stimulation increased (P < 0.05) the relative abundance of ARGs and mobile genetic elements (MGEs), such as tet(W/N/W), APH(3')-IIIa, ErmB, tet (44), ANT (6)-Ia, tet(O), tet (32), Vang_ACT_CHL, myrA, ANT (6)-Ib, IncQ1, tniB, and rep2 in cecal contents. However, the difference disappeared (P > 0.05) when NCLE was added at the same time. These differential ARGs and MGEs were mainly correlated (P < 0.01) with Clostridiales bacterium, Lachnospiraceae bacterium, and Candidatus Woodwardibium gallinarum. These species increased in LPS-stimulated broilers and decreased when NCLE was applied at the same time. In feces, LPS stimulation decreased (P < 0.05) the relative abundance of tet(Q), adeF, ErmF, Mef(En2), OXA-347, tet (40), npmA, tmrB, CfxA3, and ISCrsp1, while the LPS + NCLE treated group showed no significant effect (P > 0.05) on these ARGs. These differential ARGs and MGEs in feces were mainly correlated (P < 0.01) with Clostridiales bacterium, Pseudoflavonifractor sp. An184, Flavonifractor sp. An10, Ruminococcaceae bacterium, etc. These species increased in LPS-stimulated broilers and increased when NCLE was applied at the same time. In conclusion, LPS stimulation and NCLE influenced microbial communities and associated ARGs in both cecal contents and feces of broilers. NCLE alleviated the change of ARGs and MGEs in LPS-induced broilers by maintaining the microbial balance.IMPORTANCEAntibiotics showed a positive effect on gut health regulation and growth performance improvement in livestock breeding, but the antimicrobial resistance threat and environment pollution problem are increasingly severe with antibiotics abuse. As alternatives, plant extract containing bioactive substances are increasingly used to improve immunity and promote productivity. However, little is known about their effects on diversity and abundance of ARGs. Here, we investigated the effects of NCLE, with effective ingredients of flavonoids, on ARGs and relevant microorganisms in cecal contents and feces of broilers treated with or without lipopolysaccharide stimulation. We found that NCLE reduced the abundance of ARGs in cecal contents of lipopolysaccharide-induced broilers by maintaining the microbial balance. This study provides a comprehensive view of cecal and fecal microbial community, ARGs, and MGEs of broiler following LPS stimulation and NCLE treatment. It might be used to understand and control ARGs dissemination in livestock production.

Evaluation of antibiotic use and analysis of ciprofloxacin and gentamicin residue in fish samples from farms in Lagos, Nigeria

Antibiotic use in aquaculture for increase yield has been established over time; however, consumption of such fish may lead to inadvertent intake of sub therapeutic doses of antibiotics. Therefore, this study aimed to investigate the extent of antibiotic use in fish farming and ciprofloxacin and gentamicin residues in fish that are consumed in Lagos, Nigeria. It was conducted in two parts: a survey of 60 fish producers to assess their use of antibiotics and an analysis of ciprofloxacin and gentamicin residues in fish organs using high-performance liquid chromatography (HPLC). The survey found that twenty-nine (48%) of the farms used antibiotics, with oxytetracycline being the most common (20%), followed by ciprofloxacin (15%); gentamicin (5%); neomycin (8.33%); and probiotics (13%). HPLC analysis of fish liver and fillet samples showed that Lagos Island had the lowest residual ciprofloxacin dose (0.3014ug/g), while Lagos mainland had the greatest residual ciprofloxacin dosage (113.78765ug/g). The mean gentamicin residue in flesh of fish from farms in Lagos Island LGA was 0.37ug/g while that obtained for liver of fish samples from Surulere LGA was 2.12ug/g). The largest (5.3240ug/g) and lowest (0.2661ug/g) residual gentamicin antibiotic concentrations were found in fishes harvested from farms located in Surulere and Lagos Island, respectively. The residue levels were within the permitted range set by the WHO, but continuous regulatory surveillance is necessary to prevent antimicrobial resistance spread and improved food safety. The study has revealed that fish produced in the study area contained residues of the commonly used antibiotics hence farmers should be encouraged to consult veterinarians in cases of disease treatment for judicious use of antibiotics while self-medication and purchase of antibiotics from vendors should be discouraged.

Analysis of Resistance Gene Diversity in the Intestinal Microbiome of Broilers from Two Types of Broiler Farms in Hebei Province, China

The crucial reservoir of antibiotic resistance genes (ARGs) within the chicken intestinal microbiome poses a serious threat to both animal and human health. In China, the overuse of antibiotics has significantly contributed to the proliferation of ARGs in the chicken intestinal microbiome, which is a serious concern. However, there has been relatively little research on the diversity of resistance genes in the chicken intestinal microbiome since the implementation of the National Pilot Work Program for Action to Reduce the Use of Veterinary Antimicrobial Drugs in China. The objective of this study was to analyze the diversity of antibiotic resistance genes carried by the chicken intestinal microbiome in both standard farms (SFs), which implement antibiotic reduction and passed national acceptance, and nonstandard farms (NSFs), which do not implement antibiotic reductions, in Hebei Province. Fresh fecal samples of broiler chickens were collected from SFs (n = 4) and NSF (n = 1) and analyzed using high-throughput qPCR technology. Our findings revealed that all five farms exhibited a wide range of highly abundant ARGs, with a total of 201 ARGs and 7 MGEs detected in all fecal samples. The dominant ARGs identified conferred resistance to aminoglycosides, macrolide-lincosamide-streptomycin B (MLSB), and tetracycline antibiotics. Cellular protection mechanisms were found to be the primary resistance mechanism for these ARGs. The analysis of the co-occurrence network demonstrated a significant positive correlation between the abundance of MGEs and ARGs. The SF samples showed a significantly lower relative abundance of certain ARGs than the NSF samples (p < 0.05). The results of this study show that the abundance of ARGs demonstrated a downward trend after the implementation of the National Pilot Work Program for Action to Reduce the Usage of Veterinary Antimicrobial Drugs in Hebei Province, China.

Microbial Community and Abundance of Selected Antimicrobial Resistance Genes in Poultry Litter from Conventional and Antibiotic-Free Farms

In this study, a culture-independent approach was applied to compare the microbiome composition and the abundance of the antimicrobial resistance genes (ARGs) aadA2 for aminoglycosides, tet(A), tet(B), tet(K), and tet(M) for tetracyclines, and mcr-1 for colistin in broiler litter samples collected from conventional and antibiotic-free flocks located in Central Italy. A total of 13 flocks and 26 litter samples, collected at the beginning and at the end of each rearing cycle, were submitted to 16s rRNA sequence analysis and quantitative PCR for targeted ARGs. Firmicutes resulted in the dominant phylum in both groups of flocks, and within it, the Clostridia and Bacilli classes showed a similar distribution. Conversely, in antibiotic-free flocks, a higher frequency of Actinobacteria class and Clostridiaceae, Lactobacillaceae, Corynebacteriaceae families were reported, while in the conventional group, routinely treated with antibiotics for therapeutic purposes, the Bacteroidia class and the Enterobacteriaceae and Bacillaceae families were predominant. All investigated samples were found to be positive for at least one ARG, with the mean values of aadA2 and tet(A) the highest in conventional flocks by a significant margin. The results suggest that antibiotic use can influence the frequency of resistance determinants and the microbial community in poultry flocks, even though other environmental factors should also be investigated more deeply in order to identify additional drivers of antimicrobial resistance.

Temporal stability and community assembly mechanisms in healthy broiler cecum

In recent years, there has been an unprecedented advancement in in situ analytical approaches that contribute to the mechanistic understanding of microbial communities by explicitly incorporating ecology and studying their assembly. In this study, we have analyzed the temporal profiles of the healthy broiler cecal microbiome from day 3 to day 35 to recover the stable and varying components of microbial communities. During this period, the broilers were fed three different diets chronologically, and therefore, we have recovered signature microbial species that dominate during each dietary regime. Since broilers were raised in multiple pens, we have also parameterized these as an environmental condition to explore microbial niches and their overlap. All of these analyses were performed in view of different parameters such as body weight (BW-mean), feed intake (FI), feed conversion ratio (FCR), and age (days) to link them to a subset of microbes that these parameters have a bearing upon. We found that gut microbial communities exhibited strong and statistically significant specificity for several environmental variables. Through regression models, genera that positively/negatively correlate with the bird's age were identified. Some short-chain fatty acids (SCFAs)-producing bacteria, including Izemoplasmatales, Gastranaerophilales, and Roseburia, have a positive correlation with age. Certain pathogens, such as Escherichia-Shigella, Sporomusa, Campylobacter, and Enterococcus, negatively correlated with the bird's age, which indicated a high disease risk in the initial days. Moreover, the majority of pathways involved in amino acid biosynthesis were also positively correlated with the bird's age. Some probiotic genera associated with improved performance included Oscillospirales; UCG-010, Shuttleworthia, Bifidobacterium, and Butyricicoccaceae; UCG-009. In general, predicted antimicrobial resistance genes (piARGs) contributed at a stable level, but there was a slight increase in abundance when the diet was changed. To the best of the authors' knowledge, this is one of the first studies looking at the stability, complexity, and ecology of natural broiler microbiota development in a temporal setting.

Early-life prophylactic antibiotic treatment disturbs the stability of the gut microbiota and increases susceptibility to H9N2 AIV in chicks

BACKGROUND

Antibiotics are widely used for prophylactic therapy and for improving the growth performance of chicken. The problem of bacterial drug resistance caused by antibiotic abuse has previously attracted extensive attention; however, the influence of early-day use of prophylactic antibiotics on the gut microflora and on the disease resistance ability in chicks has not been explored. Here, we comprehensively evaluate the growth performance, gut microbial dynamics, level of antibiotic resistance genes (ARGs) in the gut microbial community, and resistance to H9N2 avian influenza virus (AIV) in chickens following long-term and short-term early-day prophylactic antibiotic treatment.

RESULTS

Unexpectedly, long-term prophylactic enrofloxacin treatment slowed the growth rate of chickens, whereas short-term antibiotics treatments were found to increase the growth rate, but these changes were not statistically significant. Strikingly, expansions of Escherichia-Shigella populations were observed in early-life prophylactic antibiotics-treated groups of chickens, which is in contrast to the general perception that antibiotics should control their pathogenicity in chicks. The gut microbiota composition of chickens treated long term with antibiotics or received early-day antibiotics treatment tend to be more dramatically disturbed compared to the gut microbiome of chickens treated with antibiotics for a short term at a later date, especially after H9N2 AIV infection.

CONCLUSIONS

Our data provide evidence that early-day and long-term antibiotic treatments have a more adverse effect on the intestinal microbiome of chickens, compared to short-term late age antibiotic treatment. Furthermore, our metagenomic data reveal that both long-term and short-term antibiotic treatment increase the relative abundance of ARGs. Our findings highlight the adverse effects of prophylactic antibiotic treatment and provide a theoretical basis for the cautious administration of antibiotics in food-producing animal management. Video Abstract.

Conditions Necessary for the Transfer of Antimicrobial Resistance in Poultry Litter

Animal manures contain a large and diverse reservoir of antimicrobial resistance (AMR) genes that could potentially spillover into the general population through transfer of AMR to antibiotic-susceptible pathogens. The ability of poultry litter microbiota to transmit AMR was examined in this study. Abundance of phenotypic AMR was assessed for litter microbiota to the antibiotics: ampicillin (Ap; 25 μg/mL), chloramphenicol (Cm; 25 μg/mL), streptomycin (Sm; 100 μg/mL), and tetracycline (Tc; 25 μg/mL). qPCR was used to estimate gene load of streptomycin-resistance and sulfonamide-resistance genes aadA1 and sul1, respectively, in the poultry litter community. AMR gene load was determined relative to total bacterial abundance using 16S rRNA qPCR. Poultry litter contained 10⁸ CFU/g, with Gram-negative enterics representing a minor population (<10⁴ CFU/g). There was high abundance of resistance to Sm (10⁶ to 10⁷ CFU/g) and Tc (10⁶ to 10⁷ CFU/g) and a sizeable antimicrobial-resistance gene load in regards to gene copies per bacterial genome (aadA1: 0.0001-0.0060 and sul1: 0.0355-0.2455). While plasmid transfer was observed from Escherichia coli R100, as an F-plasmid donor control, to the Salmonella recipient in vitro, no AMR Salmonella were detected in a poultry litter microcosm with the inclusion of E. coli R100. Confirmatory experiments showed that isolated poultry litter bacteria were not interfering with plasmid transfer in filter matings. As no R100 transfer was observed at 25 °C, conjugative plasmid pRSA was chosen for its high plasmid transfer frequency (10^-4 to 10^-5) at 25 °C. While E. coli strain background influenced the persistence of pRSA in poultry litter, no plasmid transfer to Salmonella was ever observed. Although poultry litter microbiota contains a significant AMR gene load, potential to transmit resistance is low under conditions commonly used to assess plasmid conjugation.

Antimicrobial resistance profiles of Escherichia coli isolated from laying hens in Zambia: implications and significance on one health

Background

Antimicrobial resistance (AMR) has been deepening in the layer poultry sector in Zambia partly due to the inappropriate use of antimicrobials. Escherichia coli (E. coli), a commensal and zoonotic bacterium, can potentially be a source of AMR.

Objectives

This study assessed the phenotypic AMR profiles of E. coli isolated from the apparent health-laying hens in Lusaka and Copperbelt provinces of Zambia.

Methods

A cross-sectional study was conducted between September 2020 and April 2021 in which 365 cloacal swabs were collected from 77-layer farms based in Lusaka and Copperbelt provinces of Zambia. E. coli isolation and identification were done using cultural and biochemical properties and confirmed using the 16S rRNA gene sequencing. Antimicrobial susceptibility testing (AST) was done using the Kirby-Bauer disc-diffusion method. Data analysis was done using WHONET 2020 and Stata v.16.1.

Results

Of the 365 samples, E. coli was isolated from 92.9% (n = 339). The AMR was detected in 96.5% (n = 327) of the isolates, of which 64.6% (n = 219) were multidrug-resistant (MDR). E. coli was highly resistant to tetracycline (54.6%) and ampicillin (54%) but showed low resistance to meropenem (0.9%), ceftazidime (6.2%) and chloramphenicol (8.8%).

Conclusion

This study found a high prevalence of E. coli resistant to some commonly used antibiotics in poultry, which is a public health concern because of the potential contamination of eggs and layers of chicken meat that enter the food chain. Urgent attention is needed, including strengthening antimicrobial stewardship and surveillance programmes in layer poultry production in Zambia.

Co-Harboring of Beta-Lactamases and mcr-1 Genes in Escherichia coli and Klebsiella pneumoniae from Healthy Carriers and Backyard Animals in Rural Communities in Ecuador

Few studies have addressed drug resistance of Enterobacterales in rural communities in developing countries. This study aimed to determine the coexistence of extended-spectrum β-lactamase (ESBL) and carbapenemase genes in Escherichia coli and Klebsiella pneumoniae strains carrying the mcr-1 gene in rural communities in Ecuador from healthy humans and their backyard animals. Sixty-two strains, thirty E. coli and thirty-two K. pneumoniae strains carrying the mcr-1 gene were selected from a previous study. PCR were performed for the presence of ESBLs and carbapenemase genes. The strains were further characterized, and the genetic relationship was studied with multi-locus sequencing typing (MLST) of seven housekeeping genes. Fifty-nine of the sixty-two mcr-1 isolates (95%) harbored at least on β-lactam resistance gene. The most prevalent ESBL genes were the bla_TEM genes (present in in 80% of the E. coli strains) and the bla_SHV gene (present in 84% of the K. pneumoniae strains). MSLT analysis revealed 28 different sequence types (ST); 15 for E. coli and 12 for K. pneumoniae, with most ST never described in humans and animals. The coexistence of mcr-1 and β-lactams resistant genes in E. coli and K. pneumoniae strains is alarming and threatens the efficacy of last-resort antibiotics. Our findings highlight backyard animals as a reservoir of mcr-1/β-lactams resistant genes.

Effects of different laying periods on airborne bacterial diversity and antibiotic resistance genes in layer hen houses

Poultry farms are a complex environment for close contact between humans and animals. Accumulating evidence has indicated that pathogens and drug resistance genes in chicken houses may pose a serious threat to public health and economic concerns. However, insufficient knowledge of the indoor aerosol microbiome and resistome profiles of layer hen houses hampers the understanding of their health effects. Environmental surveillance of antibiotic resistance may contribute to a better understanding and management of the human exposure risk of bioaerosols under the environmental conditions of chicken houses. In addition, the chicken house has a long operation cycle, and the bacterial diversity and antibiotic resistance genes of aerosols in different periods may be different. In this study, air samples were collected from 18 chicken houses on three farms, including the early laying period (EL), peak laying period (PL), and late laying period (LL). 16S rRNA gene sequencing and metagenomics were used to study the composition of the bacteria and resistome in aerosols of layer hen houses and the results showed that they varied with laying period. The highest alpha diversity of bacteria was observed in PL bioaerosols. The dominant bacterial phyla included Firmicutes, Bacteroidetes and Proteobacteria. Three potential pathogenic bacterial genera (Bacteroides, Corynebacterium and Fusobacterium) were found. The most abundant ARG type was aminoglycosides in all laying periods. In total, 22 possible ARG host genera were detected. ARG subtypes and abundance were both higher in LL. Network analysis also showed higher co-occurrence patterns between the bacteria and resistome in bioaerosols. The laying period plays an important role in the bacterial community and resistome in layer house aerosols.

Deciphering risks of resistomes and pathogens in intensive laying hen production chain

Antimicrobial resistance (AMR) and pathogens derived from food animals and their associated environments have emerged as challenging threats to humans from a health perspective, but our understanding of these risks and their key prevention and control points in the current intensive breeding industry remains poor. By creating an integral composition and risk profile of the resistome and microbiome through metagenomics in feces, flies, dust, sewage, and soil along the four-stage laying hen production chain, we found that the whole production chain is a hotspot for antimicrobial resistance genes (ARGs) with 374 known subtypes and pathogens, including 157 human pathogenic bacteria (HPB). Feces and flies were identified as major risk sources for these contaminations. Also, we confirmed a twin-risk of AMR and pathogenicity prevailing throughout the chain, but with different frequencies in each stage; thus, high-risk ARGs in the young chicken stage and highly prioritized HPB in the chick stage contributed 37.33 % to the total AMR risk and 36.36 % to the pathogenic risks, respectively, thus rendering the two stages to be the key prevention points. Moreover, the prevalence of 112 binned ARG supercarriers (for example, Klebsiella pneumoniae harboring 20 ARGs) was unraveled along the production chain, especially in feces, flies, and dust, and 87 potential hosts exhibited high pathogenic risk, high-risk AMR, or both, with 262 ARGs and 816 virulence factor genes. Overall, this study provides first-hand comprehensive data on high-risk ARGs and their pathogenic hosts in the intensive laying hen production chain, and thus is fundamentally important for developing new measures to help control the global AMR crisis induced through the animal-environment-human pathway.

Exploiting a targeted resistome sequencing approach in assessing antimicrobial resistance in retail foods

BACKGROUND

With the escalating risk of antimicrobial resistance (AMR), there are limited analytical options available that can comprehensively assess the burden of AMR carried by clinical/environmental samples. Food can be a potential source of AMR bacteria for humans, but its significance in driving the clinical spread of AMR remains unclear, largely due to the lack of holistic-yet-sensitive tools for surveillance and evaluation. Metagenomics is a culture-independent approach well suited for uncovering genetic determinants of defined microbial traits, such as AMR, present within unknown bacterial communities. Despite its popularity, the conventional approach of non-selectively sequencing a sample's metagenome (namely, shotgun-metagenomics) has several technical drawbacks that lead to uncertainty about its effectiveness for AMR assessment; for instance, the low discovery rate of resistance-associated genes due to their naturally small genomic footprint within the vast metagenome. Here, we describe the development of a targeted resistome sequencing method and demonstrate its application in the characterization of the AMR gene profile of bacteria associated with several retail foods.

RESULT

A targeted-metagenomic sequencing workflow using a customized bait-capture system targeting over 4,000 referenced AMR genes and 263 plasmid replicon sequences was validated against both mock and sample-derived bacterial community preparations. Compared to shotgun-metagenomics, the targeted method consistently provided for improved recovery of resistance gene targets with a much-improved target detection efficiency (> 300-fold). Targeted resistome analyses conducted on 36 retail-acquired food samples (fresh sprouts, n = 10; ground meat, n = 26) and their corresponding bacterial enrichment cultures (n = 36) reveals in-depth features regarding the identity and diversity of AMR genes, most of which were otherwise undetected by the whole-metagenome shotgun sequencing method. Furthermore, our findings suggest that foodborne Gammaproteobacteria could be the major reservoir of food-associated AMR genetic determinants, and that the resistome structure of the selected high-risk food commodities are, to a large extent, dictated by microbiome composition.

CONCLUSIONS

For metagenomic sequencing-based surveillance of AMR, the target-capture method presented herein represents a more sensitive and efficient approach to evaluate the resistome profile of complex food or environmental samples. This study also further implicates retail foods as carriers of diverse resistance-conferring genes indicating a potential impact on the dissemination of AMR.

Effect of Enrofloxacin on the Microbiome, Metabolome, and Abundance of Antibiotic Resistance Genes in the Chicken Cecum

Enrofloxacin is an important antibiotic for the treatment of Salmonella infections in livestock and poultry. However, the effects of different concentrations of enrofloxacin on the bacterial and metabolite compositions of the chicken gut and changes in the abundance of resistance genes in cecum contents remain unclear. To investigate the effects of enrofloxacin on chickens, we orally administered different concentrations of enrofloxacin to 1-day-old chickens and performed 16S rRNA gene sequencing to assess changes in the gut microbiomes of chickens after treatment. The abundance of fluoroquinolone (FQ) resistance genes was measured using quantitative PCR. Metabolomics techniques were used to examine the cecal metabolite composition. We found that different concentrations of enrofloxacin had different effects on cecum microorganisms, with the greatest effect on cecum microbial diversity in the low-concentration enrofloxacin group at day 7. Enrofloxacin use reduced the abundance of beneficial bacteria such as Lactobacillaceae and Oscillospira. Furthermore, cecum microbial diversity was gradually restored as the chickens grew. In addition, enrofloxacin increased the abundance of resistance genes, and there were differences in the changes in abundance among different antibiotic resistance genes. Moreover, enrofloxacin significantly affected linoleic acid metabolism, amino acid metabolism, and signaling pathways. This study helps improve our understanding of how antibiotics affect host physiological activities and provides new insights into the rational use of drugs in poultry farming. The probiotics and metabolites that we identified could be used to modulate the negative effects of antibiotics on the host, which requires further study. IMPORTANCE In this study, we investigated changes in the cecum flora, metabolites, and abundances of fluoroquinolone antibiotic resistance genes in chickens following the use of different concentrations of enrofloxacin. These results were used to determine the effects of enrofloxacin on chick physiology and the important flora and metabolites that might contribute to these effects. In addition, these results could help in assessing the effect of enrofloxacin concentrations on host metabolism. Our findings could help guide the rational use of antibiotics and mitigate the negative effects of antibiotics on the host.

Microplastics existence intensified bloom of antibiotic resistance in livestock feces transformed by black soldier fly

Efficient degradation of residual antibiotics in livestock and poultry feces by black soldier flies (BSFs) has been widely reported. Nevertheless, the effects of widely detected microplastics in feces on the dynamic reduction of antibiotics and the transfer of gut bacterial resistome remain unclear. In this study, red fluorescence-labeled microplastics are observed to be abundantly distributed in BSFs gut, which caused epithelial cell damage along with gut peristalsis and friction, thereby releasing reactive oxygen species and activating the antioxidant enzyme system. In addition, they result in not only in inflammatory cytokine release to induce gut inflammation, but fecal hardening because of mucus released from the BSFs, thereby hindering organic mineralization and antibiotic degradation. Besides, the gut pathogenic bacteria easily obtain growth energy and crowded out ecological niches by reducing nitrate produced by inflammatory host cells to nitrite with nitrate reductase. Consequently, linear discriminant analysis effect size and detrended correspondence analysis found that microplastic intake significantly reshape the microbial community structure and cause the significant reduction of several important organic-decomposing bacteria and probiotics (e.g., Pseudomonadales, Coriobacteriales, Lachnospirales, and Ruminococcaceae). In addition, a large number of pathogenic bacteria (e.g., Enterococcaceae, Hungateiclostridiaceae, and Clostridia) are enriched in feces and BSFs gut. Weighted correlation network analysis and bubble diagram analysis indicate that microplastic intake intensified gut colonization of pathogenic bacteria carrying antibiotic-resistant genes/mobile genetic elements, driving the bloom of antibiotic resistance in transformed fecal piles. Therefore, microplastics in feces should be isolated as much as possible before insect transformation.

Effects of litter from antimicrobial-fed broiler chickens on soil bacterial community structure and diversity

This study examined changes in soil bacterial community composition and diversity in response to fertilization with litter from chickens fed diet with no antibiotics, bambermycin, penicillin, bacitracin, salinomycin, and mix of salinomycin and bacitracin. Litter was applied to 24 agricultural-plots. Non-fertilized plots were used as a negative control. Soil samples collected from the studied plots were used to quantify Escherichia coli by plate counts, and Clostridium perfringens by qPCR. The 16S-rRNA gene sequencing was performed for microbiota analysis. Following litter application in December, the population size of E.coli was 5.4 log CFU/g, however, regardless of treatments the result revealed 5.2 and 1.4 log CFU/g of E.coli in soil sampled in January and March, respectively. Fertilization with antibiotic treated litter increased (P < 0.05) the relative abundance of Proteobacteria, Actinobacteria and Firmicutes in soil, but decreased Acidobacteria and Verrucomicrobia groups. The alpha-diversity parameters were higher (P < 0.05) in non-fertilized soil compared to the fertilized ones, suggesting that litter application was a major factor in shaping the soil bacterial communities. These results may help develop efficient litter management strategies like composting, autoclaving, or anaerobic digestion of poultry litter before application to land for preservation of soil health and crop productivity.

Antibiotic Resistance of Bacterial Isolates from Smallholder Poultry Droppings in the Guinea Savanna Zone of Nigeria

There is a growing risk of antibiotic resistance (AR) in smallholder poultry (SP). This study, therefore, aimed to investigate AR pattern of bacterial isolates from SP in the Guinea Savanna agro-ecological zone of Nigeria. A total of 120 fresh poultry droppings were aseptically collected, randomly, from two tropically adapted (FUNAAB Alpha and Noiler) and local chickens. The chickens were raised either using ethnoveterinary medicines (n = 60) or antibiotics (n = 60). Bacterial isolates were characterized and analyzed using standard protocols, and appropriate statistical tools. Compared to Pseudomonas spp. (2.5%) and Klebsiella spp. (5.8%), Salmonella spp. (57.5%) and Escherichia coli (34.2%) were the most prevalent (χ2 = 96.67; p < 0.001). Prevalence of bacterial species was significantly (p = 0.024; Odds Ratio = 2.552) influenced by antibiotics usage. All four species were multi-drug resistant. In total, 30% of the isolates had a multiple AR index ≥ 0.2. Bacterial isolates from FUNAAB Alpha (58.0%) and Noiler (44.0%) were highly resistant to quinolones, while isolates from the local chickens (22.6%) were most resistant to aminoglycosides. Bacterial species isolated from FUNAAB Alpha and local chickens exhibited the lowest and highest percentage of AR, respectively. Clustering of isolates with similar antibiogram revealed inter-species dependence with possibility for inter-species gene transfer. These findings provide a background to investigate the metagenomics of local and improved chickens for AR.

Prevalence of ESKAPE pathogens in the environment: Antibiotic resistance status, community-acquired infection and risk to human health

The ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) pathogens are characterised by increased levels of resistance towards multiple classes of first line and last-resort antibiotics. Although these pathogens are frequently isolated from clinical environments and are implicated in a variety of life-threatening, hospital-associated infections; antibiotic resistant ESKAPE strains have been isolated from environmental reservoirs such as surface water, wastewater, food, and soil. Literature on the persistence and subsequent health risks posed by the ESKAPE isolates in extra-hospital settings is however, limited and the current review aims to elucidate the primary reservoirs of these pathogens in the environment, their antibiotic resistance profiles, and the link to community-acquired infections. Additionally, information on the current state of research regarding health-risk assessments linked to exposure of the ESKAPE pathogens in the natural environment, is outlined.

Effects of Dietary Antimicrobial Growth Promoters on Performance Parameters and Abundance and Diversity of Broiler Chicken Gut Microbiome and Selection of Antibiotic Resistance Genes

Antimicrobial growth promoters (AGPs) are commonly used in broiler production. There is a huge societal concern around their use and their contribution to the proliferation of antimicrobial resistance (AMR) in food-producing animals and dissemination to humans or the environment. However, there is a paucity of comprehensive experimental data on their impact on poultry production and the AMR resistome. Here, we investigated the effect of five antimicrobial growth promoters (virginiamycin, chlortetracycline, bacitracin methyl disalicylate, lincomycin, and tylosin) used in the commercial broiler production in the Indian subcontinent and in the different parts of the world for three consecutive production cycles on performance variables and also the impact on gut bacteria, bacteriophage, and resistome profile using culture-independent approaches. There was no significant effect of AGPs on the cumulative growth or feed efficiency parameters at the end of the production cycles and cumulative mortality rates were also similar across groups. Many antibiotic resistance genes (ARGs) were ubiquitous in the chicken gut irrespective of AGP supplementation. In total, 62 ARGs from 15 antimicrobial classes were detected. Supplementation of AGPs influenced the selection of several classes of ARGs; however, this was not correlated necessarily with genes relevant to the AGP drug class; some AGPs favored the selection of ARGs related to antimicrobials not structurally related to the AGP. AGPs did not impact the gut bacterial community structure, including alpha or beta diversity significantly, with only 16-20 operational taxonomic units (OTUs) of bacteria being altered significantly. However, several AGPs significantly reduced the population density of some of the potential pathogenic genera of bacteria, such as Escherichia coli. Chlortetracycline increased the abundance of Escherichia phage, whereas other AGPs did not influence the abundance of bacteriophage significantly. Considering the evidence that AGPs used in poultry production can select for resistance to more than one class of antimicrobial resistance, and the fact that their effect on performance is not significant, their use needs to be reduced and there is a need to monitor the spread of ARGs in broiler chicken farms.

Metatranscriptomic Analysis of the Chicken Gut Resistome Response to In-Feed Antibiotics and Natural Feed Additives

The emergence of resistance against common antibiotics in the gut microbiota is a major issue for both human and livestock health. This highlights the need for understanding the impact of such application on the reservoir of antibiotic resistance genes in poultry gut and devising means to circumvent the potential resistome expansion. Phytogenic feed additives (PFAs) are potential natural alternative to antibiotic to improve animal health and performance, supposedly via positively affecting the gut microbial ecosystem, but there is little systematic information available. In this time-course study, we applied a shotgun meta-transcriptomics approach to investigate the impact of a PFA product as well as the commonly used antibiotic, zinc bacitracin either at AGP concentration or therapeutic concentration on the gut microbiome and resistome of broiler chickens raised for 35 days. Over the course of the trial, PFA treatments increased the abundance of Firmicutes such as Lactobacillus and resulted in a lower abundance of Escherichia, while the latter group increased significantly in the feces of chickens that received either AGP or AB doses of bacitracin. Tetracycline resistance and aminoglycoside resistance were the predominant antibiotic resistance gene (ARG) classes found, regardless of the treatment. PFA application resulted in a decrease in abundance of ARGs compared to those in the control group and other antibiotic treatment groups. In summary, the findings from this study demonstrate the potential of phytogenic feed additives could be an alternative to antibiotics in poultry farming, with the added benefit of counteracting antimicrobial resistance development.

Outer Membrane Vesicles of Avian PathogenicEscherichia coli Mediate the Horizontal Transmission of blaCTX-M-55

The CTX-M-55 type extended-spectrum β-lactamase (ESBL) producing Enterobacteriaceae is increasing in prevalence worldwide without the transmission mechanism being fully clarified, which threatens public and livestock health. Outer membrane vesicles (OMVs) have been shown to mediate the gene horizontal transmission in some species. However, whether bla_CTX-M-55 can be transmitted horizontally through OMVs in avian pathogenic Escherichia coli (APEC) has not been reported yet. To test this hypothesis, an ESBL-producing APEC was isolated and whole-genome sequencing (WGS) was performed to analyze the location of bla_CTX-M-55. Ultracentrifugation and size exclusion chromatography was used to isolate and purify OMVs, and the transfer experiment of bla_CTX-M-55 via OMVs was performed finally. Our results showed that the bla_CTX-M-55 was located on an IncI2 plasmid. The number and diameter of OMVs secreted by ESBL-producing APEC treated with different antibiotics were significantly varied. The transfer experiment showed that the OMVs could mediate the horizontal transfer of bla_CTX-M-55, and the frequency of gene transfer ranged from 10⁻⁵ to 10⁻⁶ CFU/mL with the highest frequency observed in the Enrofloxacin treatment group. These findings contribute to a better understanding of the antibiotics in promoting and disseminating resistance in the poultry industry and support the restrictions on the use of antibiotics in the poultry industry.

Spatial and temporal dynamics of microbiomes and resistomes in broiler litter stockpiles

Farmers apply broiler chicken litter to soils to enrich organic matter and provide crops with nutrients, following varying periods of stockpiling. However, litter frequently harbors fecal-derived microbial pathogens and associated antibiotic resistance genes (ARGs), and may be a source of microbial contamination of produce. We coupled a cutting-edge Loop Genomics long-read 16S rRNA amplicon-sequencing platform with high-throughput qPCR that targeted a suite of ARGs, to assess temporal (five time points over a 60-day period) and spatial (top, middle and bottom layers) microbiome and resistome dynamics in a broiler litter stockpile. We focused on potentially pathogenic species from the Enterobacteriaceae, Enterococcaceae and Staphylococcaceae families associated with food-borne disease. Bacterial diversity was significantly lower in the middle of the stockpile, where targeted pathogens were lowest and Bacillaceae were abundant. E. coli was the most abundant Enterobacteriaceae species, and high levels of the opportunistic pathogen Enterococcus faecium were detected. Correlation analyses revealed that the latter was significantly associated with aminoglycoside (aac(6′)-Ib(aka aacA4), aadA5), tetracycline (tetG), vancomycin (vanC), phenicol (floR) and MLSB (mphB) resistance genes. Staphylococcaceae were primarily non-pathogenic, but extremely low levels of the opportunistic pathogen S. aureus were detected, as was the opportunistic pathogen S. saprophyticus, which was linked to vancomycin (vanSA, vanC1), MLSB (vatE, ermB) and tetracycline (tetK) resistance genes. Collectively, we found that stockpile microbiomes and resistomes are strongly dictated by temporal fluctuations and spatial heterogeneity. Insights from this study can be exploited to improve stockpile management practice to support sustainable antimicrobial resistance mitigation policies in the future.