The Natural History of Integrons

Cross-environmental cycling of antimicrobial resistance in agricultural areas fertilized with poultry litter: A one health approach

Poultry litter, commonly used as an organic fertilizer, can contain antimicrobial residues, resistant bacteria, and/or antimicrobial resistance genes. After application to soil, these contaminants can reach crops and be transported to aquatic systems through leaching and runoff. Once in water bodies, they can return to soil and crops through irrigation, establishing a cycle that promotes the selection, spread and persistence of antimicrobial resistance. To investigate the hypothesis of a cyclical event, samples of poultry litter, cultivable soil fertilized with this organic residue, rhizosphere soil from Sechium edule (chayote), water, and sediments from irrigation ponds were collected across two agricultural and poultry-producing areas during the dry and rainy seasons. Clinically significant bacteria, especially bacteria belonging to the Enterobacteriaceae family, were isolated. Fifty-three strains exhibited one or more antimicrobial resistance genes, as detected by PCR amplification, including those conferring resistance to sulfonamides (sul1 and sul2), fluoroquinolones (qnrB, qnrA, and qnrS), and β-lactams (blaGES, blaTEM, blaSHV, blaCTX-M-1/2,blaCTX-M-8, and blaCTX-M-14). Genes encoding integrases related to class-1 and 2 integrons (intI1 and intI2) were also observed. A rare occurrence of the blaGES gene was observed in Stenotrophomonas sp. and Brevundimonas sp. Strains of Escherichia sp. were multidrug resistant. Sequencing of the 16S rRNA encoding gene indicated unique operational taxonomic units (OTUs) originating from poultry litter and found in the soil, rhizosphere, water, and sediment, highlighting the dissemination of this material across agricultural substrates. These findings strongly suggest the spread of antimicrobial-resistant bacteria in agricultural environments, posing potential risks to both human and animal health.

A Comprehensive Study on the Distribution of Integrons and Their Gene Cassettes in Clinical Isolates

Antibiotic resistance is a significant global health concern, leading to increased morbidity, mortality, and health care costs. Integrons are genetic elements that could acquire and express gene cassettes, including those that confer antibiotic resistance. This comprehensive study focused on the distribution of integrons and their gene cassettes in clinical isolates. This study explored the structure and classification of integrons with particular emphasis on Class I, II, III, and IV integrons. It also discussed the role of integrons in antibiotic resistance. The findings of this study contribute to a better understanding of the mechanisms underlying antibiotic resistance and provide valuable insights for developing strategies to combat this public health crisis.

A TaqMan real-time PCR assay for detection of qacEΔ1 gene in Gram-negative bacteria

The transfer of biocide and antibiotic resistance genes by mobile genetic elements is the most common mechanism for rapidly acquiring and spreading resistance among bacteria. The qacEΔ1 gene confers the resistance to quaternary ammonium compounds (QACs). It has also been considered a genetic marker for the presence of class 1 integrons associated with multidrug-resistant (MDR) phenotypes in Gram-negative bacteria. In this study, a TaqMan real-time PCR assay was developed to detect the qacEΔ1 gene in Gram-negative bacteria. The assay has a detection limit of 80 copies of the qacEΔ1 gene per reaction. No false-positive or false-negative results have been observed. Simultaneous amplification and detection of the 16S rRNA gene is performed as an endogenous internal amplification control (IAC). The TaqMan real-time PCR assay developed is a rapid, sensitive, and specific method that could be used to monitor resistance to QACs, the spread of class 1 integrons, and the prediction of associated MDR phenotypes in Gram-negative bacteria.

Water chlorination increases the relative abundance of an antibiotic resistance marker in developing sourdough starters

Multiple factors explain the proper development of sourdough starters. Although the role of raw ingredients and geography, among other things, have been widely studied recently, the possible effect of air quality and water chlorination on the overall bacterial communities associated with sourdough remains to be explored. Here, using 16S rRNA amplicon sequencing, we show that clean, filtered-air severely limited the presence of lactic acid bacteria in sourdough starters, suggesting that surrounding air is an important source of microorganisms necessary for the development of sourdough starters. We also show that water chlorination at levels commonly found in drinking water systems has a limited impact on the overall bacterial communities developing in sourdough starters. However, using targeted sequencing, which offers a higher resolution, we found that the abundance of integron 1, a genetic mechanism responsible for the horizontal exchange of antibiotic-resistance genes in spoilage and pathogenic bacteria, increased significantly with the level of water chlorination. Although our results suggest that water chlorination might not impact sourdough starters at a deep phylogenetic level, they indicate that it can favor the spread of genetic elements associated with spoilage bacteria.

IMPORTANCE

Proper development of sourdough starters is critical for making tasty and healthy bread. Although many factors contributing to sourdough development have been studied, the effect of water chlorination on the bacterial communities in sourdough has been largely ignored. Researchers used sequencing techniques to investigate this effect and found that water chlorination at levels commonly found in drinking water systems has a limited impact on the overall bacterial communities developing in sourdough starters. However, they discovered that water chlorination could increase the abundance of integron 1, a genetic mechanism responsible for the horizontal exchange of antibiotic resistance genes in spoilage and pathogenic bacteria. This suggests that water chlorination could favor the growth of key spoilage bacteria and compromise the quality and safety of the bread. These findings emphasize the importance of considering water quality when developing sourdough starters for the best possible bread.

High-throughput microfluidic quantitative PCR system for the simultaneous detection of antibiotic resistance genes and bacterial and viral pathogens in wastewater

Comprehensive data on bacterial and viral pathogens of diarrhea and studies applying culture-independent methods for examining antibiotic resistance in wastewater are lacking. This study aimed to simultaneously quantify antibiotic resistance genes (ARGs), class 1 integron-integrase (int1), bacterial and viral pathogens of diarrhea, 16S rRNA, and other indicators using a high-throughput quantitative PCR (HT-qPCR) system. Thirty-six grab wastewater samples from a wastewater treatment plant in Japan, collected three times a month between August 2022 and July 2023, were centrifuged, followed by nucleic acid extraction, reverse transcription, and HT-qPCR. Fourteen targets were included, and HT-qPCR was performed on the Biomark X9™ System (Standard BioTools). For all qPCR assays, R2 was ≥0.978 and the efficiencies ranged from 90.5% to 117.7%, exhibiting high performance. Of the 36 samples, 20 (56%) were positive for Norovirus genogroup II (NoV-GII), whereas Salmonella spp. and Campylobacter jejuni were detected in 24 (67%) and Campylobacter coli in 13 (36%) samples, with mean concentrations ranging from 3.2 ± 0.8 to 4.7 ± 0.3 log10 copies/L. NoV-GII detection ratios and concentrations were higher in winter and spring. None of the pathogens of diarrhea correlated with acute gastroenteritis cases, except for NoV-GII, suggesting the need for data on specific bacterial infections to validate bacterial wastewater-based epidemiology (WBE). All samples tested positive for sul1, int1, and blaCTX-M, irrespective of season. The less explored blaNDM-1 showed a wide prevalence (>83%) and consistent abundance ranging from 4.3 ± 1.0 to 4.9 ± 0.2 log10 copies/L in all seasons. sul1 was the predominant ARG, whereas absolute abundances of 16S rRNA, int1, and blaCTX-M varied seasonally. int1 was significantly correlated with blaCTX-M in autumn and spring, whereas it showed no correlation with blaNDM-1, questioning the applicability of int1 as a sole indicator of overall resistance determinants. This study exhibited that the HT-qPCR system is pivotal for WBE.

Correlation between the spread of IMP-producing bacteria and the promoter strength of blaIMP genes

The first report of transmissible carbapenem resistance encoded by blaIMP-1 was discovered in Pseudomonas aeruginosa GN17203 in 1988, and blaIMP-1 has since been detected in other bacteria, including Enterobacterales. Currently, many variants of blaIMPs exist, and point mutations in the blaIMP promoter have been shown to alter promoter strength. For example, the promoter (Pc) of blaIMP-1, first reported in P. aeruginosa GN17203, was a weak promoter (PcW) with low-level expression intensity. This study investigates whether point mutations in the promoter region have helped to create strong promoters under antimicrobial selection pressure. Using bioinformatic approaches, we retrieved 115 blaIMPs from 14,529 genome data of Pseudomonadota and performed multiple alignment analyses. The results of promoter analysis of the 115 retrieved blaIMPs showed that most of them used the Pc located in class 1 integrons (n = 112, 97.4%). The promoter analysis by year revealed that the blaIMP population with the strong promoter, PcS, was transient. In contrast, the PcW-TG population, which had acquired a TGn-extended -10 motif in PcW and had an intermediate promoter strength, gradually spread throughout the world. An inverse correlation between Pc promoter strength and Intl1 integrase excision efficiency has been reported previously [1]. Because of this trade-off, it is unlikely that blaIMPs with strong promoters will increase rapidly, but the possibility that promoter strength will increase with the use of other integrons cannot be ruled out. Monitoring of the blaIMP genes, including promoter analysis, is necessary for global surveillance of carbapenem-resistant bacteria.

Horizontal gene transfer in plant microbiomes: integrons as hotspots for cross-species gene exchange

Plant microbiomes play important roles in plant health and fitness. Bacterial horizontal gene transfer (HGT) can influence plant health outcomes, driving the spread of both plant growth-promoting and phytopathogenic traits. However, community dynamics, including the range of genetic elements and bacteria involved in this process are still poorly understood. Integrons are genetic elements recently shown to be abundant in plant microbiomes, and are associated with HGT across broad phylogenetic boundaries. They facilitate the spread of gene cassettes, small mobile elements that collectively confer a diverse suite of adaptive functions. Here, we analysed 5,565 plant-associated bacterial genomes to investigate the prevalence and functional diversity of integrons in this niche. We found that integrons are particularly abundant in the genomes of Pseudomonadales, Burkholderiales, and Xanthomonadales. In total, we detected nearly 9,000 gene cassettes, and found that many could be involved in plant growth promotion or phytopathogenicity, suggesting that integrons might play a role in bacterial mutualistic or pathogenic lifestyles. The rhizosphere was enriched in cassettes involved in the transport and metabolism of diverse substrates, suggesting that they may aid in adaptation to this environment, which is rich in root exudates. We also found that integrons facilitate cross-species HGT, which is particularly enhanced in the phyllosphere. This finding may provide an ideal opportunity to promote plant growth by fostering the spread of genes cassettes relevant to leaf health. Together, our findings suggest that integrons are important elements in plant microbiomes that drive HGT, and have the potential to facilitate plant host adaptation.

In vitro assessment of the bacterial stress response and resistance evolution during multidrug-resistant bacterial invasion of the Xenopus tropicalis intestinal tract under typical stresses

The intestinal microbiome might be both a sink and source of resistance genes (RGs). To investigate the impact of environmental stress on the disturbance of exogenous multidrug-resistant bacteria (mARB) within the indigenous microbiome and proliferation of RGs, an intestinal conjugative system was established to simulate the invasion of mARB into the intestinal microbiota in vitro. Oxytetracycline (OTC) and heavy metals (Zn, Cu, Pb), commonly encountered in aquaculture, were selected as typical stresses for investigation. Adenosine 5'-triphosphate (ATP), hydroxyl radical (OH·-) and extracellular polymeric substance (EPS) were measured to investigate their influence on the acceptance of RGs by intestinal bacteria. The results showed that the transfer and diffusion of RGs under typical combined stressors were greater than those under a single stressor. Combined effect of OTC and heavy metals (Zn, Cu) significantly increased the activity and extracellular EPS content of bacteria in the intestinal conjugative system, increasing intI3 and RG abundance. OTC induced a notable inhibitory response in Citrobacter and exerted the proportion of Citrobacter and Carnobacterium in microbiota. The introduction of stressors stimulates the proliferation and dissemination of RGs within the intestinal environment. These results enhance our comprehension of the typical stresses effect on the RGs dispersal in the intestine.

Microbial biofilms on macroalgae harbour diverse integron gene cassettes

Integrons are genetic platforms that capture, rearrange and express mobile modules called gene cassettes. The best characterized gene cassettes encode antibiotic resistance, but the function of most integron gene cassettes remains unknown. Functional predictions suggest that many gene cassettes could encode proteins that facilitate interactions with other cells and with the extracellular environment. Because cell interactions are essential for biofilm stability, we sequenced gene cassettes from biofilms growing on the surface of the marine macroalgae Ulva australis and Sargassum linearifolium. Algal samples were obtained from coastal rock platforms around Sydney, Australia, using seawater as a control. We demonstrated that integrons in microbial biofilms did not sample genes randomly from the surrounding seawater, but harboured specific functions that potentially provided an adaptive advantage to both the bacterial cells in biofilm communities and their macroalgal host. Further, integron gene cassettes had a well-defined spatial distribution, suggesting that each bacterial biofilm acquired these genetic elements via sampling from a large but localized pool of gene cassettes. These findings suggest two forms of filtering: a selective acquisition of different integron-containing bacterial species into the distinct biofilms on Ulva and Sargassum surfaces, and a selective retention of unique populations of gene cassettes at each sampling location.

Detection of resistance integrons among biofilm and non-biofilm producing clinical isolates of Pseudomonas aeruginosa

Introduction

Integrons are genetic systems that may confer antibiotic resistance to Pseudomonas aeruginosa. Biofilm formation can facilitate gene exchange and can accelerate the development of antibiotic resistance. The aim of this work was to assess the distribution of resistance integrons including class 1, 2 and 3 among biofilm- and non-biofilm producing clinical strains of P. aeruginosa. We also aimed to investigate the relationship between the existence of these integrons and the isolates' resistance patterns.

Methods

Specimens were obtained from patients showing evidence of infection. P. aeruginosa isolates were identified using conventional techniques, while disk diffusion test was used to detect their antimicrobial susceptibilities. Biofilm formation was detected by the tissue culture plate technique, while classes of integrons were detected by polymerase chain reaction.

Results

Out of 106 P. aeruginosa isolates, 55.7% were class 1 integron-positive while 19.8% were class 2 integron-positive. However, class 3 integrons were not detected. Significant associations were found between class 1 integrons and resistance toward amikacin, gentamicin, cefepime, ceftazidime and ciprofloxacin. Class 2 integrons were associated with amikacin, ceftazidime and cefepime resistance. Of pseudomonal isolates, 61.3% were biofilm producing. Biofilm production was associated significantly with the existence of class 1 integrons (p<0.001) and class 2 integrons (p=0.039).

Conclusions

About two thirds of isolated strains harbored resistance integrons, which emphasized their significance in our locality. The frequencies of class 1 and 2 integrons were significantly higher among biofilm forming isolates. Ongoing surveillance and infection control strategies are necessary to limit spread of integrons.

Functional enrichment of integrons: Facilitators of antimicrobial resistance and niche adaptation

Integrons are genetic elements, found among diverse bacteria and archaea, that capture and rearrange gene cassettes to rapidly generate genetic diversity and drive adaptation. Despite their broad taxonomic and geographic prevalence, and their role in microbial adaptation, the functions of gene cassettes remain poorly characterized. Here, using a combination of bioinformatic and experimental analyses, we examined the functional diversity of gene cassettes from different environments. We find that cassettes encode diverse antimicrobial resistance (AMR) determinants, including those conferring resistance to antibiotics currently in the developmental pipeline. Further, we find a subset of cassette functions is universally enriched relative to their broader metagenomes. These are largely involved in (a)biotic interactions, including AMR, phage defense, virulence, biodegradation, and stress tolerance. The remainder of functions are sample-specific, suggesting that they confer localised functions relevant to their microenvironment. Together, they comprise functional profiles different from bulk metagenomes, representing niche-adaptive components of the prokaryotic pangenome.

Multiplex Hybrid Capture Improves the Deep Detection of Antimicrobial Resistance Genes from Wastewater Treatment Plant Effluents to Assess Environmental Issues

Metagenomic sequencing (mDNA-seq) is one of the best approaches to address antimicrobial resistance (AMR) issues and characterize AMR genes (ARGs) and their host bacteria (ARB); however, the sensitivity provided is insufficient for the overall detection in wastewater treatment plant (WWTP) effluents because the effluent is well treated. This study investigated the multiplex hybrid capture (xHYB) method (QIAseq × HYB AMR Panel) and its potential to increase AMR assessment sensitivity. The mDNA-Seq analysis suggested that the WWTP effluents had an average of 104 reads per kilobase of gene per million (RPKM) for the detection of all targeted ARGs, whereas xHYB significantly improved detection at 601,576 RPKM, indicating an average 5,805-fold increase in sensitivity. For instance, sul1 was detected at 15 and 114,229 RPKM using mDNA-seq and xHYB, respectively. The blaCTX-M, blaKPC, and mcr gene variants were not detected by mDNA-Seq but were detected by xHYB at 67, 20, and 1,010 RPKM, respectively. This study demonstrates that the multiplex xHYB method could be a suitable evaluation standard with high sensitivity and specificity for deep-dive detection, highlighting a broader illustration of ongoing dissemination in the entire community.

Occurrence of extended-spectrum β-lactamases-producing Escherichia coli isolates over gradient pollution in an urban tropical estuary

Bacterial resistance to antimicrobials is a global public health problem that surpasses the human context and can be increased by pollution. However, the lack of systematic monitoring of resistance in some aquatic matrices, such as tropical estuaries, makes it unknown whether its occurrence is associated with anthropogenic pollution in these environments. Therefore, we investigated the occurrence of extended-spectrum beta-lactamases (ESBLs) producing Escherichia coli as a resistance indicator for 12 consecutive months at three representative points of a pollution gradient in Guanabara Bay (GB), Brazil. Sixty-six E. coli strains were selected from 72 samples of GB waters in the presence of ceftriaxone (8 μg mL-1 ) and identified by MALDI-TOF MS. Of the 66, 55 (83.3%) strains were ESBL producers. They carried beta-lactamase/ESBL genes, with the predominance of blaCTX-M (54, 98.2%), especially the blaCTX-M-1,2 allele (49.1%). These strains were detected frequently (81.8%) from the point with the highest pollution levels. Furthermore, the marker for Class 1 integron, intI1 gene, was detected in 54.5% of ESBL producers. These data suggest an association between antimicrobial-resistant E. coli and sewage pollution in aquatic environments raising concerns about the possible risks of human exposure to these waters and fish consumption.

The biotechnological potential of Aeromonas: a bird's eye view

The genus Aeromonas comprises Gram-negative bacilli widely distributed in aquatic habitats that can also be found in the terrestrial environment and in close association with humans and animals. Aeromonas spp. are particularly versatile bacteria, with high genomic plasticity and notable capacity to adapt to different environments and extreme conditions. On account of being mostly associated with their pathogenic potential, research on the biotechnological potentialities of Aeromonas spp. is considerably scarce when compared to other bacterial groups. Nonetheless, studies over the years have been hinting at several interesting hidden potentialities in this bacterial group, especially with the recent advances in whole-genome sequencing, unveiling Aeromonas spp. as interesting candidates for the discovery of novel industrial biocatalysts, bioremediation strategies, and biopolyester production. In this context, the present study aims to provide an overview of the main biotechnological applications reported in the genus Aeromonas and provide new insights into the further exploration of these frequently overlooked, yet fascinating, bacteria.

Tracing the Sources and Prevalence of Class 1 Integrons, Antimicrobial Resistance, and Trace Elements Using European Honey Bees

Surveillance of antimicrobial resistance is essential for an effective One Health response. This study explores the efficacy of European honey bees (Apis mellifera) for biomonitoring antimicrobial resistance (AMR) in urban areas. Class 1 integrons (intI1) are investigated as a universal AMR indicator, as well as associated cassette arrays and trace element contaminants at a city-wide scale. Class 1 integrons were found to be pervasive across the urban environment, occurring in 52% (75/144) of the honey bees assessed. The area of waterbodies within the honey bee's foraging radius was associated with intI1 prevalence, indicating an exposure pathway for future investigation to address. Trace element concentrations in honey bees reflected urban sources, supporting the application of this biomonitoring approach. As the first study of intI1 in honey bees, we provide insights into the environmental transfer of bacterial DNA to a keystone species and demonstrate how intI1 biomonitoring can support the surveillance of AMR.

Antimicrobial susceptibility and integrons detection among extended-spectrum β-lactamase producing Enterobacteriaceae isolates in patients with urinary tract infection

Background

Integrons are bacterial mobile genetic components responsible for mediating the antibiotic resistance process by carrying and spreading antimicrobial resistance genes among bacteria through horizontal gene transfer.

Objectives

This cross-sectional hospital-based study aimed to find the prevalence of antibiotic resistance patterns and to detect integrons classes (I, II, and III) among bacterial isolates in patients with urinary tract infections (UTI) in Sulaimani, Iraq.

Patients and Methods

Mid-stream urine samples (no. = 400) were collected from patients with UTI at three different Hospitals from Sulaimani, Iraq, between September 2021 to January 2022. Urine samples were cultured on various agar media, and grown bacteria were isolated. Antibiotic susceptibility test (AST) and an extended-spectrum β-lactamase (ESBL) screen were done for isolated bacteria. Then, integrons classes were screened using conventional PCR with gene sequencing and uploaded to the National Center for Biotechnology Information (NCBI).

Results

The frequency rate of Enterobacteriaceae was 67.03% among positive urine cultures. E. coli (no. = 86) and Klebsiella pneumoniae (no. = 32) isolates were identified. The most sensitive antibiotics were the carbapenem group (85.3%) and nitrofurantoin (NFN) (64.2%), while the most resistant antibiotics were nalidixic acid (NA) and 3^rd generation cephalosporin. The occurrence rate of ESBL was 56.6% with a predominance of class I integron (54.2%), then class II (15.8%) and no positive record for class III integron were observed.

Conclusion

Most bacterial isolates from patients with UTI produced class I and II integrons genes with favourable ESBL properties.

Profiling of Antimicrobial Resistance Genes and Integron from Escherichia coli Isolates Using Whole Genome Sequencing

This study is designed to investigate Escherichia coli for the antibiotic resistance genes (ARGs) and integrons from healthy as well as diarrhoeic/diseased animals/birds' faecal samples. A total of eight samples were selected for the study; from each animal, two samples were taken, one from healthy animals/birds and one from diarrhoeic/diseased animals/birds. Antibiotic sensitivity testing (AST) and whole genome sequencing (WGS) was performed for selected isolates. The E. coli isolates showed resistance to moxifloxacin, followed by erythromycin, ciprofloxacin, pefloxacin, tetracycline, levofloxacin, ampicillin, amoxicillin, and sulfadiazine (4/8, 50.00% each). The E. coli isolates were 100% sensitive to amikacin, followed by chloramphenicol, cefixime, cefoperazone, and cephalothin. A total of 47 ARGs from 12 different antibiotic classes were detected among the eight isolates by WGS. The different classes of antibiotics included aminoglycoside, sulphonamide, tetracycline, trimethoprim, quinolone, fosfomycin, phenicol, macrolide, colistin, fosmidomycin, and multidrug efflux. The class 1 integrons were detected in 6/8 (75.00%) isolates with 14 different gene cassettes.

Uncovering Bacterial Hosts of Class 1 Integrons in an Urban Coastal Aquatic Environment with a Single-Cell Fusion-Polymerase Chain Reaction Technology

Horizontal gene transfer (HGT) is a key driver of bacterial evolution via transmission of genetic materials across taxa. Class 1 integrons are genetic elements that correlate strongly with anthropogenic pollution and contribute to the spread of antimicrobial resistance (AMR) genes via HGT. Despite their significance to human health, there is a shortage of robust, culture-free surveillance technologies for identifying uncultivated environmental taxa that harbor class 1 integrons. We developed a modified version of epicPCR (emulsion, paired isolation, and concatenation polymerase chain reaction (PCR)) that links class 1 integrons amplified from single bacterial cells to taxonomic markers from the same cells in emulsified aqueous droplets. Using this single-cell genomic approach and Nanopore sequencing, we successfully assigned class 1 integron gene cassette arrays containing mostly AMR genes to their hosts in coastal water samples that were affected by pollution. Our work presents the first application of epicPCR for targeting variable, multigene loci of interest. We also identified the Rhizobacter genus as novel hosts of class 1 integrons. These findings establish epicPCR as a powerful tool for linking taxa to class 1 integrons in environmental bacterial communities and offer the potential to direct mitigation efforts toward hotspots of class 1 integron-mediated dissemination of AMR.

Molecular characterization of class 1 integrons in carbapenem-resistant Enterobacterales isolates

OBJECTIVE

Carbapenem-resistant Enterobacterales (CRE) infections result in higher treatment costs and mortality rates. Integrons play important roles in emergence and spread of antibiotic resistant genes. To get a better understand on the effects of integron on CRE resistance, distribution of common carbapenemase genes and class 1 integron in clinical CRE isolates were investigated.

METHOD

Carbapenemase genes, including bla_KPC, bla_VIM, bla_IMP, bla_NDM, bla_GES, bla_VEB and bla_OXA-23, were screened in 161 CRE isolates and subtypes of these genes were confirmed through sequence analysis. Class 1 integron was screened and common promoter and gene cassette arrays were determined by sequencing. The resistant rates to clinical commonly used antibiotics between integron positive and integron negative CRE isolates were compared.

RESULTS

Of 161 CRE isolates, the most prevalent carbapenemase gene was bla_KPC-2, which was detected in 139 isolates, including 99 Klebsiella pneumoniae. Class 1 integron was detected in 78 isolates. Twenty different gene cassettes, including two carbapenemase genes bla_VEB-1 and bla_IMP-4, and nine different gene cassette arrays, including bla_VEB-1-aadB-arr-2-cmlA5-bla_OXA-10-aadA1, aadB-catB8-bla_OXA-10-aadA1-dfrA1-aacA4 and bla_IMP-4-qacG-aacA4-catB3, were detected. Five types of common promoters were identified. Relative weak promoter PcH1 was the dominant type. Resistant rates of CRE isolates containing class 1 integrons to ceftazidime, amikacin, trimethoprim/sulfamethoxazole and gentamicin were higher than those without class 1 integrons (P < 0.05).

CONCLUSION

Class 1 integrons play important roles in the emergence and spread of CRE resistance. To the best of our knowledge, this is the first report of aadB-catB8-bla_OXA-10-aadA1-dfrA1-aacA4 and bla_IMP-4-qacG-aacA4-catB3 in the same Providencia rettgeri isolate and bla_VEB-1-aadB-arr-2-cmlA5-bla_OXA-10-aadA1 in P. rettgeri.

Horizontal Gene Transfer of Antibiotic Resistance Genes in Biofilms

Most bacteria attach to biotic or abiotic surfaces and are embedded in a complex matrix which is known as biofilm. Biofilm formation is especially worrisome in clinical settings as it hinders the treatment of infections with antibiotics due to the facilitated acquisition of antibiotic resistance genes (ARGs). Environmental settings are now considered as pivotal for driving biofilm formation, biofilm-mediated antibiotic resistance development and dissemination. Several studies have demonstrated that environmental biofilms can be hotspots for the dissemination of ARGs. These genes can be encoded on mobile genetic elements (MGEs) such as conjugative and mobilizable plasmids or integrative and conjugative elements (ICEs). ARGs can be rapidly transferred through horizontal gene transfer (HGT) which has been shown to occur more frequently in biofilms than in planktonic cultures. Biofilm models are promising tools to mimic natural biofilms to study the dissemination of ARGs via HGT. This review summarizes the state-of-the-art of biofilm studies and the techniques that visualize the three main HGT mechanisms in biofilms: transformation, transduction, and conjugation.

Fate of Horizontal-Gene-Transfer Markers and Beta-Lactamase Genes during Thermophilic Composting of Human Excreta

Thermophilic composting is a suitable treatment for the recycling of organic wastes for agriculture. However, using human excreta as feedstock for composting raises concerns about antibiotic resistances. We analyzed samples from the start and end of a thermophilic composting trial of human excreta, together with green cuttings and straw, with and without biochar. Beta-lactamase genes bla_CTX-M, bla_IMP, and bla_TEM conferring resistance to broad-spectrum beta-lactam antibiotics, as well as horizontal gene transfer marker genes, intI1 and korB, were quantified using qPCR. We found low concentrations of the beta-lactamase genes in all samples, with non-significant mean decreases in bla_CTX-M and bla_TEM copy numbers and a mean increase in bla_IMP copy numbers. The decrease in both intI1 and korB genes from start to end of composting indicated that thermophilic composting can decrease the horizontal spread of resistance genes. Thus, thermophilic composting can be a suitable treatment for the recycling of human excreta.

Identification of integrons and gene cassette-associated recombination sites in bacteriophage genomes

Bacteriophages are versatile mobile genetic elements that play key roles in driving the evolution of their bacterial hosts through horizontal gene transfer. Phages co-evolve with their bacterial hosts and have plastic genomes with extensive mosaicism. In this study, we present bioinformatic and experimental evidence that temperate and virulent (lytic) phages carry integrons, including integron-integrase genes, attC/attI recombination sites and gene cassettes. Integrons are normally found in Bacteria, where they capture, express and re-arrange mobile gene cassettes via integron-integrase activity. We demonstrate experimentally that a panel of attC sites carried in virulent phage can be recognized by the bacterial class 1 integron-integrase (IntI1) and then integrated into the paradigmatic attI1 recombination site using an attC x attI recombination assay. With an increasing number of phage genomes projected to become available, more phage-associated integrons and their components will likely be identified in the future. The discovery of integron components in bacteriophages establishes a new route for lateral transfer of these elements and their cargo genes between bacterial host cells.

Hiding in Plain Sight: Characterization of Aeromonas Species Isolated from a Recreational Estuary Reveals the Carriage and Putative Dissemination of Resistance Genes

Antimicrobial resistance (AMR) has become one of the greatest challenges worldwide, hampering the treatment of a plethora of infections. Indeed, the AMR crisis poses a threat to the achievement of the United Nations' Sustainable Development Goals and, due to its multisectoral character, a holistic approach is needed to tackle this issue. Thus, the investigation of environments beyond the clinic is of utmost importance. Here, we investigated thirteen strains of antimicrobial-resistant Aeromonas isolated from an urban estuary in Brazil. Most strains carried at least one antimicrobial resistance gene and 11 carried at least one heavy metal resistance gene. Noteworthy, four (30.7%) strains carried the bla_KPC gene, coding for a carbapenemase. In particular, the whole-genome sequence of Aeromonas hydrophila strain 34SFC-3 was determined, revealing not only the presence of antimicrobial and heavy metal resistance genes but also a versatile virulome repertoire. Mobile genetic elements, including insertion sequences, transposons, integrative conjugative elements, and an IncQ1 plasmid were also detected. Considering the ubiquity of Aeromonas species, their genetic promiscuity, pathogenicity, and intrinsic features to endure environmental stress, our findings reinforce the concept that A. hydrophila truly is a "Jack of all trades'' that should not be overlooked under the One Health perspective.

Class 1 integron and related antimicrobial resistance gene dynamics along a complex freshwater system affected by different anthropogenic pressures

The risk for human health posed by polluted aquatic environments, and especially those carrying antibiotic resistance genes (ARGs) of clinical interest, is still debated. This is because of our limited knowledge of the dynamics of antimicrobial resistance in the environment, the selection mechanisms underlying the spread of ARGs, and the ecological factors potentially favoring their return to humans. The Class 1 integron is one of the most effective platforms for the dissemination of ARGs. In this study we investigated a freshwater system consisting of a lake-river-lake continuum, determining the abundance of class 1 integrons and their associated ARGs by a modulated metagenomic approach. Bacterial abundance and community composition were used to identify the potential carriers of class 1 integrons and their associated ARGs over a period of six months. Class 1 integrons and their ARG cargoes were significantly more abundant in riverine sampling sites receiving treated wastewater. Further, class 1 integrons carried ARGs ranked at the highest risk for human health (e.g., catB genes), in particular, genes encoding resistance to aminoglycosides. Genera of potential pathogens, such as Pseudomonas and Escherichia-Shigella, were correlated with class 1 integrons. The lake-river-lake system demonstrated a clear relationship between the integrase gene of class 1 integrons (intI1) and anthropogenic impact, but also a strong environmental filtering that favored the elimination of intI1 once the human derived stressors were reduced. Overall, the results of this study underline the role class 1 integrons as proxy of anthropogenic pollution and suggest this genetic platform as an important driver of aminoglycoside resistance genes, including high risk ARGs, of potential concern for human health.

Discovery of Highly Trimethoprim-Resistant DfrB Dihydrofolate Reductases in Diverse Environmental Settings Suggests an Evolutionary Advantage Unrelated to Antibiotic Resistance

Type B dihydrofolate reductases (DfrB) are intrinsically highly resistant to the widely used antibiotic trimethoprim, posing a threat to global public health. The ten known DfrB family members have been strongly associated with genetic material related to the application of antibiotics. Several dfrB genes were associated with multidrug resistance contexts and mobile genetic elements, integrated both in chromosomes and plasmids. However, little is known regarding their presence in other environments. Here, we investigated the presence of dfrB beyond the traditional areas of enquiry by conducting metagenomic database searches from environmental settings where antibiotics are not prevalent. Thirty putative DfrB homologues that share 62 to 95% identity with characterized DfrB were identified. Expression of ten representative homologues verified trimethoprim resistance in all and dihydrofolate reductase activity in most. Contrary to samples associated with the use of antibiotics, the newly identified dfrB were rarely associated with mobile genetic elements or antibiotic resistance genes. Instead, association with metabolic enzymes was observed, suggesting an evolutionary advantage unrelated to antibiotic resistance. Our results are consistent with the hypothesis that multiple dfrB exist in diverse environments from which dfrB were mobilized into the clinically relevant resistome. Our observations reinforce the need to closely monitor their progression.

Discovery of integrons in Archaea: Platforms for cross-domain gene transfer

Horizontal gene transfer between different domains of life is increasingly being recognized as an important evolutionary driver, with the potential to increase the pace of biochemical innovation and environmental adaptation. However, the mechanisms underlying the recruitment of exogenous genes from foreign domains are mostly unknown. Integrons are a family of genetic elements that facilitate this process within Bacteria. However, they have not been reported outside Bacteria, and thus their potential role in cross-domain gene transfer has not been investigated. Here, we discover that integrons are also present in 75 archaeal metagenome-assembled genomes from nine phyla, and are particularly enriched among Asgard archaea. Furthermore, we provide experimental evidence that integrons can facilitate the recruitment of archaeal genes by bacteria. Our findings establish a previously unknown mechanism of cross-domain gene transfer whereby bacteria can incorporate archaeal genes from their surrounding environment via integron activity. These findings have important implications for prokaryotic ecology and evolution.

Plasmids as Key Players in Acinetobacter Adaptation

This review briefly summarizes the data on the mechanisms of development of the adaptability of Acinetobacters to various living conditions in the environment and in the clinic. A comparative analysis of the genomes of free-living and clinical strains of A. lwoffii, as well as the genomes of A. lwoffii and A. baumannii, has been carried out. It has been shown that plasmids, both large and small, play a key role in the formation of the adaptability of Acinetobacter to their living conditions. In particular, it has been demonstrated that the plasmids of various strains of Acinetobacter differ from each other in their structure and gene composition depending on the lifestyle of their host bacteria. Plasmids of modern strains are enriched with antibiotic-resistant genes, while the content of genes involved in resistance to heavy metals and arsenic is comparable to plasmids from modern and ancient strains. It is concluded that Acinetobacter plasmids may ensure the survival of host bacteria under conditions of various types of environmental and clinical stresses. A brief overview of the main mechanisms of horizontal gene transfer on plasmids inherent in Acinetobacter strains is also given.

Inverse PCR-based detection reveal novel mobile genetic elements and their associated genes in the human oral metagenome

The human oral cavity is one of the hotspots harboring multiple mobile genetic elements (MGEs), which are segments of DNA that can move either within bacterial genomes or between bacterial cells that can facilitate the spreading of genetic materials, including antimicrobial resistance genes. It is, therefore, important to investigate genes associated with the MGEs as they have a high probability of dissemination within the bacterial population under selective pressure from human activities. As one-third of oral bacteria are not yet culturable in the laboratory condition, therefore, in this work, it is aimed to detect and identify the genetic contexts of MGEs in the oral cavity through an inverse PCR (IPCR)-based approach on the oral metagenomic. The human oral metagenome was extracted from saliva samples collected from healthy individuals in Tromsø, Norway. The extracted DNA was partially digested with the HindIII restriction enzyme and self-circularized by ligation. DNA primers targeting each MGE were designed to amplify outwards from the MGEs and used for the IPCR on the circularized DNA products. The IPCR amplicons were cloned into a pCR-XL-2-TOP vector, screened, and sequenced. Out of 40 IPCR amplicons, we confirmed and verified the genetic contexts of 11 samples amplified with primers targeting integron gene cassettes (GCs), IS431 composite transposons, and Tn916 conjugative transposons (tet(M) and xis-int). Novel integron GCs, MGEs, and variants of Tn916 conjugative transposons were identified, which is the first report using the IPCR technique to detect the genetic contexts of MGEs in the oral metagenomic DNA.

Novel Mobile Integrons and Strain-Specific Integrase Genes within Shewanella spp. Unveil Multiple Lateral Genetic Transfer Events within The Genus

Shewanella spp. are Gram-negative bacteria that thrive in aquatic niches and also can cause infectious diseases as opportunistic pathogens. Chromosomal (CI) and mobile integrons (MI) were previously described in some Shewanella isolates. Here, we evaluated the occurrence of integrase genes, the integron systems and their genetic surroundings in the genus. We identified 22 integrase gene types, 17 of which were newly described, showing traits of multiple events of lateral genetic transfer (LGT). Phylogenetic analysis showed that most of them were strain-specific, except for Shewanella algae, where SonIntIA-like may have co-evolved within the host as typical CIs. It is noteworthy that co-existence of up to five different integrase genes within a strain, as well as their wide dissemination to Alteromonadales, Vibrionales, Chromatiales, Oceanospirillales and Enterobacterales was observed. In addition, identification of two novel MIs suggests that continuous LGT events may have occurred resembling the behavior of class 1 integrons. The constant emergence of determinants associated to antimicrobial resistance worldwide, concomitantly with novel MIs in strains capable to harbor several types of integrons, may be an alarming threat for the recruitment of novel antimicrobial resistance gene cassettes in the genus Shewanella, with its consequent contribution towards multidrug resistance in clinical isolates.

Methods for the targeted sequencing and analysis of integrons and their gene cassettes from complex microbial communities

Integrons are microbial genetic elements that can integrate mobile gene cassettes. They are mostly known for spreading antibiotic resistance cassettes among human pathogens. However, beyond clinical settings, gene cassettes encode an extraordinarily diverse range of functions important for bacterial adaptation. The recovery and sequencing of cassettes has promising applications, including: surveillance of clinically important genes, particularly antibiotic resistance determinants; investigating the functional diversity of integron-carrying bacteria; and novel enzyme discovery. Although gene cassettes can be directly recovered using PCR, there are no standardised methods for their amplification and, importantly, for validating sequences as genuine integron gene cassettes. Here, we present reproducible methods for the amplification, sequence processing, and validation of gene cassette amplicons from complex communities. We describe two different PCR assays that either amplify cassettes together with integron integrases, or gene cassettes together within cassette arrays. We compare the performance of Nanopore and Illumina sequencing, and present bioinformatic pipelines that filter sequences to ensure that they represent amplicons from genuine integrons. Using a diverse set of environmental DNAs, we show that our approach can consistently recover thousands of unique cassettes per sample and up to hundreds of different integron integrases. Recovered cassettes confer a wide range of functions, including antibiotic resistance, with as many as 300 resistance cassettes found in a single sample. In particular, we show that class one integrons are collecting and concentrating resistance genes out of the broader diversity of cassette functions. The methods described here can be applied to any environmental or clinical microbiome sample.

Carriage of antibiotic resistant bacteria in endangered and declining Australian pinniped pups

The rapid emergence of antimicrobial resistance (AMR) is a major concern for wildlife and ecosystem health globally. Genetic determinants of AMR have become indicators of anthropogenic pollution due to their greater association with humans and rarer presence in environments less affected by humans. The objective of this study was to determine the distribution and frequency of the class 1 integron, a genetic determinant of AMR, in both the faecal microbiome and in Escherichia coli isolated from neonates of three pinniped species. Australian sea lion (Neophoca cinerea), Australian fur seal (Arctocephalus pusillus doriferus) and long-nosed fur seal (Arctocephalus forsteri) pups from eight breeding colonies along the Southern Australian coast were sampled between 2016-2019. DNA from faecal samples (n = 309) and from E. coli (n = 795) isolated from 884 faecal samples were analysed for class 1 integrons using PCRs targeting the conserved integrase gene (intI) and the gene cassette array. Class 1 integrons were detected in A. p. doriferus and N. cinerea pups sampled at seven of the eight breeding colonies investigated in 4.85% of faecal samples (n = 15) and 4.52% of E. coli isolates (n = 36). Integrons were not detected in any A. forsteri samples. DNA sequencing of the class 1 integron gene cassette array identified diverse genes conferring resistance to four antibiotic classes. The relationship between class 1 integron carriage and the concentration of five trace elements and heavy metals was also investigated, finding no significant association. The results of this study add to the growing evidence of the extent to which antimicrobial resistant bacteria are polluting the marine environment. As AMR determinants are frequently associated with bacterial pathogens, their occurrence suggests that these pinniped species are vulnerable to potential health risks. The implications for individual and population health as a consequence of AMR carriage is a critical component of ongoing health investigations.