Integrons: past, present, and future

Characterization of antibiotic resistance integrons harbored by Romanian Escherichia coli uropathogenic strains

Because little is known about the integrons which constitute an important means of spreading resistance in bacteria circulating in Romania, this study aimed to detect antibiotic resistance gene cassettes embedded in integrons in a convenient collection of 60 ciprofloxacin-resistant Escherichia coli isolates of various phylogroups, associated with community-acquired urinary tract infections. Characterization of the integrons was accomplished by PCR, restriction fragment length polymorphism typing, and DNA sequencing of each identified type. More than half of the tested E. coli strains were positive for integrons of class 1 (31 strains) or 2 (1 strain). These strains derived more frequently from phylogenetic groups A (15 of 21 strains), B1 (10 of 14 strains), and F (3 of 4 strains), respectively. While 20 strains carried class 1 integrons which could be assigned to nine types, eleven strains carried integrons that lacked the 3’-end conserved segment. The attempts made to characterize the gene cassettes located within the variable region of the various integrons identified in this study revealed the presence of genes encoding resistance to trimethoprim, aminoglycosides, beta-lactams or chloramphenicol. The evidence of transferable resistance determinants already established in the autochthonous E. coli strains highlights the need for improved control of resistance-carrying bacteria.

A comprehensive survey of integron-associated genes present in metagenomes

Background

Integrons are genomic elements that mediate horizontal gene transfer by inserting and removing genetic material using site-specific recombination. Integrons are commonly found in bacterial genomes, where they maintain a large and diverse set of genes that plays an important role in adaptation and evolution. Previous studies have started to characterize the wide range of biological functions present in integrons. However, the efforts have so far mainly been limited to genomes from cultivable bacteria and amplicons generated by PCR, thus targeting only a small part of the total integron diversity. Metagenomic data, generated by direct sequencing of environmental and clinical samples, provides a more holistic and unbiased analysis of integron-associated genes. However, the fragmented nature of metagenomic data has previously made such analysis highly challenging.

Results

Here, we present a systematic survey of integron-associated genes in metagenomic data. The analysis was based on a newly developed computational method where integron-associated genes were identified by detecting their associated recombination sites. By processing contiguous sequences assembled from more than 10 terabases of metagenomic data, we were able to identify 13,397 unique integron-associated genes. Metagenomes from marine microbial communities had the highest occurrence of integron-associated genes with levels more than 100-fold higher than in the human microbiome. The identified genes had a large functional diversity spanning over several functional classes. Genes associated with defense mechanisms and mobility facilitators were most overrepresented and more than five times as common in integrons compared to other bacterial genes. As many as two thirds of the genes were found to encode proteins of unknown function. Less than 1% of the genes were associated with antibiotic resistance, of which several were novel, previously undescribed, resistance gene variants.

Conclusions

Our results highlight the large functional diversity maintained by integrons present in unculturable bacteria and significantly expands the number of described integron-associated genes.

Antimicrobial resistance and virulence of Pseudomonas spp. among healthy animals: concern about exolysin ExlA detection

Pseudomonas is a ubiquitous genus that also causes human, animal and plant diseases. Most studies have focused on clinical P. aeruginosa strains from humans, but they are scarce on animal strains. This study was aimed to determine the occurrence of Pseudomonas spp. among faecal samples of healthy animals, and to analyse their antimicrobial resistance, and pathogenicity. Among 704 animal faecal samples analysed, 133 Pseudomonas spp. isolates (23 species) were recovered from 46 samples (6.5%), and classified in 75 different PFGE patterns. Low antimicrobial resistance levels were found, being the highest to aztreonam (50.3%). Five sequence-types (ST1648, ST1711, ST2096, ST2194, ST2252), two serotypes (O:3, O:6), and three virulotypes (analysing 15 virulence and quorum-sensing genes) were observed among the 9 P. aeruginosa strains. Type-3-Secretion System genes were absent in the six O:3-serotype strains that additionally showed high cytotoxicity and produced higher biofilm biomass, phenazine pigments and motility than PAO1 control strain. In these six strains, the exlAB locus, and other virulence genotypes (e.g. RGP69 pathogenicity island) exclusive of PA7 outliers were detected by whole genome sequencing. This is the first description of the presence of the ExlA exolysin in P. aeruginosa from healthy animals, highlighting their pathological importance.

Dynamics of class 1 integrons in aerobic biofilm reactors spiked with antibiotics

Class 1 integrons are strongly associated with the dissemination of antibiotic resistance in bacteria. However, little is known about whether the presence of antibiotics affects the abundance of integrons and antibiotic resistance genes during biological wastewater treatment. To explore the roles of class 1 integrons in spreading antibiotic resistance genes in environmental compartments, the dynamics of integrons were followed in biofilm reactors treating synthetic wastewater respectively spiked with streptomycin (STM) and oxytetracycline (OTC). The relative abundance of the integron-integrase gene (intI1) increased 12 or 29-fold respectively when treated with STM or OTC, under incrementally increasing dosage regimes from 0 to 50 mg L^-1. Significant increases in intI1 abundance initially occurred at an antibiotic dose of 0.1 mg L^-1. At the beginning of the experiment, 51% to 64% of integrons carried no gene cassettes. In STM and OTC spiked systems, there was a significant increase in the proportion of integrons that contained resistance gene cassettes, particularly at intermediate and higher antibiotic concentrations. Gene cassettes encoding resistance to aminoglycosides, trimethoprim, beta-lactam, erythromycin, and quaternary ammonium compounds were all detected in the treated systems. Three tetracycline resistance genes (tetA, tetC, tetG) were significantly correlated with the abundance of intI1 (p < 0.01), despite no tet resistance being present as a gene cassette. Genome sequencing of isolates showed synteny between the tet resistance genes and intI1, mediated through linkage to transposable elements including Tn3, IS26 and ISCR3. Class 1 integrons appeared to be under positive selection in the presence of antibiotics, and might have actively acquired new gene cassettes during the experiment.

Role of integrons in the proliferation of multiple drug resistance in selected bacteria occurring in poultry production

1. The increase in microbial resistance, and in particular multiple drug resistance (MDR), is an increasing threat to public health. The uncontrolled use of antibiotics and antibacterial chemotherapeutics in the poultry industry, especially in concentrations too low to cause inhibition, and the occurrence of residues in feed and in the environment play a significant role in the development of resistance among zoonotic food-borne microorganisms.2. Determining the presence and transmission methods of resistance in bacteria is crucial for tracking and preventing antibiotic resistance. Horizontal transfer of genetic elements responsible for drug resistance is considered to be the main mechanism for the spread of antibiotic resistance.3. Of the many well-known genetic elements responsible for horizontal gene transfer, integrons are among the most important factors contributing to multiple drug resistance. The mechanism of bacterial drug resistance acquisition through integrons is one of the essential elements of MDR prevention in animal production.

Subsistence and complexity of antimicrobial resistance on a community-wide level

There are a multitude of resistance strategies that microbes can apply to avoid inhibition by antimicrobials. One of these strategies is the enzymatic modification of the antibiotic, in a process generally termed inactivation. Furthermore, some microorganisms may not be limited to the mere inactivation of the antimicrobial compounds. They can continue by further enzymatic degradation of the compounds' carbon backbone, taking nutritional and energetic advantage of the former antibiotic. This driving force to harness an additional food source in a complex environment adds another level of complexity to the reasonably well-understood process of antibiotic resistance proliferation on a single cell level: It brings bioprotection into play at the level of microbial community. Despite the possible implications of a resistant community in a host and a lurking antibiotic failure, knowledge of degradation pathways of antibiotics and their connections is scarce. Currently, it is limited to only a few families of antibiotics (e.g. β-lactams and sulfonamides). In this article, we discuss the fluctuating nature of the relationship between antibiotic resistance and the biodegradation of antibiotics. This distinction mainly depends on the genetic background of the microbe, as general resistance genes can be recruited to function in a biodegradation pathway.

Antibiotic resistance genes and bacterial community dynamics in the seawater environment of Dapeng Cove, South China

In recent years, the propagation of antibiotic resistance genes (ARGs) and increased antibiotic resistance in pathogens have gained serious attention. Numerous reports have investigated the influence of domestic sewage discharge, medical wastewater and aquaculture wastewater on rivers and lakes, while the dynamics of ARGs in seawater and the relationships between ARGs, bacterial community structure and environmental factors have been less thoroughly described. In this study, the abundance, distribution and source of ARGs, as well as the relationships between ARGs, bacterial community changes and environmental factors in the seawater environment and sediment of Dapeng Cove, were investigated. Real-time quantitative PCR and Illumina Miseq sequencing technology were applied to determine the effects of the production cycle of cage culture, tourism and seasonality on ARGs. Chloramphenicol resistance genes (floR, cmlA) and sulfonamide resistance genes (sul1) were the dominant resistance genes in water and sediment. Pearson's correlation analysis showed that the abundance of all ARGs and the integrase I gene intI1 was positively correlated with chemical oxygen demand and suspended solids. Class 1 integrons might facilitate the dissemination of ARGs, and intI1 was detected in all samples at high concentrations. In aqueous environments, Cyanobacteria, Proteobacteria and Bacteroidetes were the dominant phyla, among which Proteobacteria and Bacteroidetes were positively correlated with the concentration of target ARGs. In the sediment, Proteobacteria, Bacteroidetes, Chloroflexi, Acidobacteria and Planctomycetes were the dominant phyla, among which Bacteroidetes and Planctomycetes were positively correlated with most of the target ARGs and had a significant influence on changes in the abundance of ARGs. The domestic sewage was the main source of ARGs in the seawater. Our results showed that bacterial community structure and environmental factors affected the distributional dynamics of ARGs. Anthropogenic activities played significant roles in promoting ARGs abundance in the seawater environments.

Photochemical fate of quaternary ammonium compounds in river water

Quaternary ammonium compounds (QACs) are not completely removed during wastewater treatment and are frequently detected in surface waters and sediments. The photochemical transformation of QACs has not been thoroughly investigated as a potential degradation pathway affecting their fate in the environment. Kinetic studies of common QACs with and without aromatic groups under simulated and natural sunlight conditions were performed with model sensitizers and dissolved organic matter to estimate photochemical half-lives in the aquatic environment. All QACs investigated react with hydroxyl radicals at diffusion-controlled rates (∼2.9 × 109 to 1.2 × 1010 M-1 s-1). Benzethonium reacted via direct photolysis (ΦBZT,outdoor = 1.7 × 10-2 (mol Ei-1)). Benzethonium also reacted with the triplet excited state model sensitizer 2-acetylnaphthalene, but evidence suggests this reaction pathway is unimportant in natural waters due to faster quenching of the triplet 2-acetylnapthalene by oxygen. Reactivity with singlet oxygen for the QACs was minimal. Overall, reactions with hydroxyl radicals will dominate over direct photolysis due to limited spectral overlap of sunlight emission and QAC absorbance. Photolysis half-lives are predicted to be 12 to 94 days, indicating slow abiotic degradation in surface water.

Whole Genome Sequencing Analysis of Porcine Faecal Commensal Escherichia coli Carrying Class 1 Integrons from Sows and Their Offspring

Intensive pig production systems often rely on the use of antimicrobials and heavy metal feed additives to maintain animal health and welfare. To gain insight into the carriage of antimicrobial resistance genes (ARGs) in the faecal flora of commercially reared healthy swine, we characterised the genome sequences of 117 porcine commensal E. coli that carried the class 1 integrase gene (intI1⁺). Isolates were sourced from 42 healthy sows and 126 of their offspring from a commercial breeding operation in Australia in 2017. intI1⁺ E. coli was detected in 28/42 (67%) sows and 90/126 (71%) piglets. Phylogroup A, particularly clonal complex 10, and phylogroup B1 featured prominently in the study collection. ST10, ST20, ST48 and ST361 were the dominant sequence types. Notably, 113/117 isolates (96%) carried three or more ARGs. Genes encoding resistance to -lactams, aminoglycosides, trimethoprim, sulphonamides, tetracyclines and heavy metals were dominant. ARGs encoding resistance to last-line agents, such as carbapenems and third generation cephalosporins, were not detected. IS26, an insertion sequence noted for its ability to capture and mobilise ARGs, was present in 108/117 (92%) intI1⁺ isolates, and it played a role in determining class 1 integron structure. Our data shows that healthy Australian pig faeces are an important reservoir of multidrug resistant E. coli that carry genes encoding resistance to multiple first-generation antibiotics and virulence-associated genes.

The effects of offshore petroleum exploitation on microbial community and antibiotic resistome of adjacent marine sediments

The exploitation of petroleum in offshore areas is becoming more prosperous due to the increasing human demand for oil. However, the effects of offshore petroleum exploitation on the microbial community in the surrounding environment are still not adequately understood. In the present study, variations in the composition, function, and antibiotic resistance of the microbial community in marine sediments adjacent to an offshore petroleum exploitation platform were analyzed by a metagenomics-based method. Significant shifts in the microbial community composition were observed in sediments impacted by offshore petroleum exploitation. Nitrosopumilales was enriched in marine sediments with the activities of offshore petroleum exploitation compared to the control sediments. The abundances of function genes involved in carbon, butanoate, methane, and fatty acid metabolism in sediment microbial communities also increased due to the offshore petroleum exploitation. Offshore petroleum exploitation resulted in the propagation of some antibiotic resistance genes (ARGs), including a multidrug transporter, smeE, and arnA, in marine sediments via horizontal gene transfer mediated by class I integrons. However, the total abundance and diversity of ARGs in marine sediments were not significantly affected by offshore petroleum exploitation. This study is the first attempt to analyze the impact of offshore petroleum exploitation on the spread of antibiotic resistance.

Horizontal Gene Transfer: From Evolutionary Flexibility to Disease Progression

Flexibility in the exchange of genetic material takes place between different organisms of the same or different species. This phenomenon is known to play a key role in the genetic, physiological, and ecological performance of the host. Exchange of genetic materials can cause both beneficial and/or adverse biological consequences. Horizontal gene transfer (HGT) or lateral gene transfer (LGT) as a general mechanism leads to biodiversity and biological innovations in nature. HGT mediators are one of the genetic engineering tools used for selective introduction of desired changes in the genome for gene/cell therapy purposes. HGT, however, is crucial in development, emergence, and recurrence of various human-related diseases, such as cancer, genetic-, metabolic-, and neurodegenerative disorders and can negatively affect the therapeutic outcome by promoting resistant forms or disrupting the performance of genome editing toolkits. Because of the importance of HGT and its vital physio- and pathological roles, here the variety of HGT mechanisms are reviewed, ranging from extracellular vesicles (EVs) and nanotubes in prokaryotes to cell-free DNA and apoptotic bodies in eukaryotes. Next, we argue that HGT plays a role both in the development of useful features and in pathological states associated with emerging and recurrent forms of the disease. A better understanding of the different HGT mediators and their genome-altering effects/potentials may pave the way for the development of more effective therapeutic and diagnostic regimes.

Probing the Mobilome: Discoveries in the Dynamic Microbiome

There has been an explosion of metagenomic data representing human, animal, and environmental microbiomes. This provides an unprecedented opportunity for comparative and longitudinal studies of many functional aspects of the microbiome that go beyond taxonomic classification, such as profiling genetic determinants of antimicrobial resistance, interactions with the host, potentially clinically relevant functions, and the role of mobile genetic elements (MGEs). One of the most important but least studied of these aspects are the MGEs, collectively referred to as the 'mobilome'. Here we elaborate on the benefits and limitations of using different metagenomic protocols, discuss the relative merits of various sequencing technologies, and highlight relevant bioinformatics tools and pipelines to predict the presence of MGEs and their microbial hosts.

Occurrence of integrons and antibiotic resistance genes in cryoconite and ice of Svalbard, Greenland, and the Caucasus glaciers

The prevalence of integrons and antibiotic resistance genes (ARGs) is a serious threat for public health in the new millennium. Although commonly detected in sites affected by strong anthropogenic pressure, in remote areas their occurrence, dissemination, and transfer to other ecosystems is poorly recognized. Remote sites are considered as a benchmark for human-induced contamination on Earth. For years glaciers were considered pristine, now they are regarded as reservoirs of contaminants, thus studies on contamination of glaciers, which may be released to other ecosystems, are highly needed. Therefore, in this study we evaluated the occurrence and frequency of clinically relevant ARGs and resistance integrons in the genomes of culturable bacteria and class 1 integron-integrase gene copy number in the metagenome of cryoconite, ice and supraglacial gravel collected on two Arctic (South-West Greenland and Svalbard) and two High Mountain (the Caucasus) glaciers. Altogether, 36 strains with intI1 integron-integrase gene were isolated. Presence of class 1 integron-integrase gene was also recorded in metagenomic DNA from all sampling localities. The mean values of relative abundance of intI1 gene varied among samples and ranged from 0.7% in cryoconite from Adishi Glacier (the Caucasus) to 16.3% in cryoconite from Greenland. Moreover, antibiotic-resistant strains were isolated from all regions. Genes conferring resistance to β-lactams (bla_SHV, bla_TEM, bla_OXA, bla_CMY), fluoroquinolones (qepA, qnrC), and chloramphenicol (cat, cmr) were detected in the genomes of bacterial isolates.

Arsenic and cadmium as predominant factors shaping the distribution patterns of antibiotic resistance genes in polluted paddy soils

Heavy metals have been recognized as potential factors driving the evolution and development of antibiotic resistance. However, the relative effects of cadmium (Cd) and arsenic (As) on the prevalence and distribution of antibiotic resistance genes (ARGs) remain unclear. We investigated the co-selection effects of Cd and As on ARGs in 45 paddy soils polluted by heavy metals, using high-throughput quantitative PCR. A total of 119 ARGs and 9 mobile genetic elements (MGEs) were detected in all samples. Regression analysis showed that the single pollution index (PI_As and PI_Cd) and Nemerow integrated pollution index (NIPI) both had significant and positive correlations with ARGs (P <  0.05), indicating the co-selective effects of Cd and As on ARGs distribution. The significant correlations between bacterial taxa and different ARGs in network analysis revealed potential hosts of ARGs. Structural equation models indicated that the effects of As on ARGs were stronger than that of Cd. The profile of ARGs could be impacted by Cd and As indirectly by strongly affecting the bacterial abundance. Overall, this study extended our knowledge about the co-selection of Cd and As on ARGs in paddy soil, and had important implications for assessing the potential risks of ARGs in paddy soils.

Characterization of antibiotic resistance genes and bacterial community in selected municipal and industrial sewage treatment plants beside Poyang Lake

Sewage treatment plants (STPs) are significant reservoirs of antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB). Municipal STPs (MSTPs) and industrial STPs (ISTPs) are the two most important STP types in cities. In this study, the ARGs, mobile genetic elements (MGEs), and bacterial communities of selected STPs, including two MSTPs and one ISTP, in the vicinity of Poyang Lake were comprehensively investigated through high-throughput qPCR and high-throughput Illumina sequencing. The results showed that the profiles of ARGs, MGEs and bacteria differed between the ISTP and the two MSTPs, most likely due to differences in influent water quality, such as the Pb that characterized in the ISTP's influent. The longer hydraulic retention times (HRTs) of the two MSTPs than of the ISTP may also have accounted for the different profiles. Thus, a prolonged HRT in the CASS process seems to allow a more extensive removal of ARGs and bacteria in ISTPs with similar treatment process. By providing comprehensive insights into the characteristics of ARGs, MGEs and the bacterial communities of the selected MSTPs and ISTP, our study provides a scientific basis for controlling the propagation and diffusion of ARGs and ARB in different types of STPs.

Genomic profiling of Escherichia coli isolates from bacteraemia patients: a 3-year cohort study of isolates collected at a Sydney teaching hospital

This study sought to assess the genetic variability of Escherichia coli isolated from bloodstream infections (BSIs) presenting at Concord Hospital, Sydney during 2013-2016. Whole-genome sequencing was used to characterize 81 E. coli isolates sourced from community-onset (CO) and hospital-onset (HO) BSIs. The cohort comprised 64 CO and 17 HO isolates, including 35 multidrug-resistant (MDR) isolates exhibiting phenotypic resistance to three or more antibiotic classes. Phylogenetic analysis identified two major ancestral clades. One was genetically diverse with 25 isolates distributed in 16 different sequence types (STs) representing phylogroups A, B1, B2, C and F, while the other comprised phylogroup B2 isolates in subclades representing the ST131, ST73 and ST95 lineages. Forty-seven isolates contained a class 1 integron, of which 14 carried blaCTX -M-gene. Isolates with a class 1 integron carried more antibiotic resistance genes than isolates without an integron and, in most instances, resistance genes were localized within complex resistance loci (CRL). Resistance to fluoroquinolones could be attributed to point mutations in chromosomal parC and gyrB genes and, in addition, two isolates carried a plasmid-associated qnrB4 gene. Co-resistance to fluoroquinolone and broad-spectrum beta-lactam antibiotics was associated with ST131 (HO and CO), ST38 (HO), ST393 (CO), ST2003 (CO) and ST8196 (CO and HO), a novel ST identified in this study. Notably, 10/81 (12.3 %) isolates with ST95 (5 isolates), ST131 (2 isolates), ST88 (2 isolates) and a ST540 likely carry IncFII-IncFIB plasmid replicons with a full spectrum of virulence genes consistent with the carriage of ColV-like plasmids. Our data indicate that IncF plasmids play an important role in shaping virulence and resistance gene carriage in BSI E. coli in Australia.

Sharing of Clinically Important Antimicrobial Resistance Genes by Companion Animals and Their Human Household Members

The aims of this study were to implement a rapid easy methodology, to characterize the antimicrobial resistance gene (AMR) gut content associated with Enterobacteriales and staphylococci; and to evaluate statistical association between AMRs present in fecal samples from healthy companion animals and their human household members. Fecal samples were collected from 27 humans and 29 companion animals living in close contact in 20 households. Nineteen healthy humans without daily contact with companion animals were the control group. After DNA extraction, β-lactamase families and 10 genes of other antimicrobial classes were screened by PCR. Furthermore, third-generation cephalosporin-resistant, carbapenem-resistant, and colistin-resistant Enterobacteriales and methicillin-resistant staphylococci were screened by bacteriological methods. The bla_TEM-1B gene with a P3 promotor was the most frequent β-lactam-resistant gene detected in humans and companion animals from households (33.3%, and 17.2%, respectively). The sul2 was the most frequently shared gene by humans and animals from the same household. In 50% of households at least one AMR was detected simultaneously in companion animal/owner pairs. Healthy humans and companion animals carried several AMRs of clinical importance. To the best our knowledge, this study reports the first detection of the bla_SHV-27 gene in fecal samples from healthy humans in Portugal and in Europe.

The Global Prevalence of Class 1 Integron and Associated Antibiotic Resistance in Escherichia coli from Patients with Urinary Tract Infections, a Systematic Review and Meta-Analysis

Objectives: The present systematic review and meta-analysis study aimed to investigate the prevalence of class 1 integrons and their associated antibiotic resistance in uropathogenic Escherichia coli. Materials and Methods: A systematic search was conducted to identify studies meeting our inclusion criteria in the Web of Science, PubMed, Embase, Scopus, and Google Scholar electronic databases to the end of July 2019. Finally, 35 articles were selected for data extraction, and meta-analysis was performed using the metaprop program in the STATA, version 11.0, software. Results: The pooled prevalence of class 1 integrons was 47% (95% confidence interval [CI]: 40-54), ranging from 6% to 90%. There was significant heterogeneity among the 35 studies (χ² = 840.37; p < 0.001; I² = 95.95%). The results of the subgroup analysis based on characterization of patients indicated that pooled prevalence of class 1 integrons was 52% (95% CI: 41-63; n = 14 studies) and 43% (95% CI: 34-54; n = 19 studies) in hospitalized and community patients, respectively. The lowest and highest prevalence of antibiotic resistance was observed for imipenem and ampicillin, respectively. According to the results of Begg's and Egger's tests, we did not find significant publication bias both in the included studies and in the subgroup analysis. Conclusions: The results show the high prevalence of class 1 integrons and high level of antibiotic resistance in association with those among uropathogenic E. coli. Moreover, the prevalence of class 1 integrons in Asian countries, as well as hospital-acquired urinary tract infection (UTI), was higher than in other countries and community-acquired UTI.

The Occurrence of Type I, II, and III Integrons in Multi-drug Resistance and Methicillin-Resistant Staphylococcus aureus Isolates in Iran

Integrons are mobilizable platforms-DNA elements with impacts on moving antibiotic resistance genes among bacteria and capable of spreading multi-drug resistance (MDR) in pathogens. Methicillin-resistant Staphylococcus aureus (MRSA) strains are the main cause of community-acquired and nosocomial infections with high mortality and morbidity rates worldwide. This work is mainly aimed at calculating the frequency of Type I, II, and III integrons within multi-drug resistance and Methicillin-resistant S. aureus Isolates in Iran. In this cross-sectional study, 230 clinical isolates of S. aureus were gathered from patients of educational hospitals in the provinces of Iran. These isolates were verified utilizing particular biochemical examinations and then assessed for antibiotic susceptibility through disk diffusion technique and standard procedures were done. Genomic and plasmid DNA of all isolates were extracted using Extraction Kit and PCR assay was used for the detection of Type I, II and III integrons genes. Out of the 230 S. aureus isolates, 136 (59.1%) isolates were MRSA and 141 (61.3%) isolates exhibited the MDR pattern. PCR and sequencing showed that 57 (24.8%) of tested isolates carry Type I integron. Among the isolates investigated, MRSA and MDR isolates showed frequencies of 56.1% and 57.9%, respectively. Type II and III integrons were found in none of 230 isolates. The IntI I gene was present in approximately one-quarter of this study isolates. The great prevalence rate of MDR and MRSA isolates and concurrently the existence of Type I integron among those isolates have been considered an important concern in medical society.

Ionic Liquid Enriches the Antibiotic Resistome, Especially Efflux Pump Genes, Before Significantly Affecting Microbial Community Structure

An expanding list of chemicals may permeabilize bacterial cells and facilitate horizontal gene transfer (HGT), which enhances propagation of antibiotic resistance genes (ARGs) in the environment. Previous studies showed that 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]), an ionic liquid, can facilitate HGT of some ARGs among bacteria. However, the dynamic response of a wider range of ARGs and associated mobile genetic elements (MGEs) in different environments is unknown. Here, we used metagenomic tools to study shifts of the resistome and microbiome in both sediments and freshwater microcosms exposed to [BMIm][PF6]. Exposure for 16 h to 0.1 or 1.0 g/L significantly enriched more than 207 ARG subtypes primarily encoding efflux pumps in freshwater microcosms as well as cultivable antibiotic-resistant bacteria. This resistome enrichment was attributed to HGT facilitated by MGEs (428 plasmids, 61 integron-integrase genes, and 45 gene cassettes were enriched) as well as to HGT-related functional genes. Interestingly, resistome enrichment occurred fast (within 16 h) after [BMIm][PF6] exposure, before any significant changes in bacterial community structure. Similar ARG enrichment occurred in sediment microcosms exposed to [BMIm][PF6] for 28 d, and this longer exposure affected the microbial community structure (e.g., Proteobacteria abundance increased significantly). Overall, this study suggests that [BMIm][PF6] releases could rapidly enrich the antibiotic resistome in receiving environments by increasing HGT and fortuitously selecting for efflux pump genes, thus contributing to ARG propagation.

Detection of New Delhi metallo-beta-lactamase enzyme gene bla NDM-1 associated with the Int-1 gene in Gram-negative bacteria collected from the effluent treatment plant of a tuberculosis care hospital in Delhi, India

Background

Organisms possessing the bla_NDM-1 gene (responsible for carbapenem resistance) with a class-1 integron can acquire many other antibiotic resistance genes from the community sewage pool and become multidrug-resistant superbugs. In this regard, hospital sewage, which contains a large quantity of residual antibiotics, metals and disinfectants, is being recognized as a significant cause of antimicrobial resistance (AMR) origination and spread across the major centres of the world and is thus routinely investigated as a marker for tracing the origin of drug resistance. Therefore, in this study, an attempt has been made to identify and characterize the carbapenem-resistant microbes associated with integron genes amongst the organisms isolated from the effluent treatment plant (ETP) installed in a tertiary respiratory care hospital in Delhi, India.

Methods

One hundred and thirty-eight organisms belonging to Escherichia, Klebsiella, Pseudomonas and Acinetobacter spp. were collected from the incoming and outgoing sewage lines of the ETP. Carbapenem sensitivity and characterization was performed by the imipenem and imipenem-EDTA disc diffusion method. Later DNA extraction and PCR steps were performed for the Int-1 and bla_NDM-1 genes.

Results

Of the 138 organisms, 86 (62.3 %) were imipenem-resistant (P<0.05). One hundred and twenty-four (89.9 %) organisms had one or both of the genes. Overall, the bla_NDM-1 gene (genotypic resistance) was present in 71 % (98/138) of organisms. 53.6 % (74/138) organisms were double gene-positive (bla_NDM-1 + Int-1), of which 40 were producing the metallo-beta-lactamase enzyme, making up almost 28.9 % (40/138) of the collected organisms.

Conclusion

The current study strengthens the hypothesis that Carbapenem resistant organisms are in a high-circulation burden through the human gut and hospital ETPs are providing an environment for resistance origination and amplification.

Environmental Distribution of AR Class 1 Integrons in Upper Adige River Catchment (Northern Italy)

The source of antibiotic residuals can be directly related to the presence of municipal or industrial wastewater and agricultural activities. Antibiotics can trigger the dissemination of antibiotic resistance genes within bacterial communities. The mobile genetic elements Class 1 integrons (intl1 region) has been already found to be correlated with a wide range of pollutants (i.e., antibiotics, heavy metals), and hence, it has been proposed as a proxy for environmental health. This study aimed to assess the presence of intl1 in different environmental matrices, including agricultural and forest soils, freshwater and unpolluted sediments in the upper Adige River catchment (N Italy), in order to identify the spread of pollutants. Intl1 was detected by direct PCR amplification at different frequencies. The urban and agricultural areas revealed the presence of intl1, except for apple orchards, where it was below the detection limit. Interestingly, intl1 was found in a presumed unpolluted environment (glacier moraine), maybe because of the high concentration of metal ions in the mineral soil. Finally, intl1 was absent in forest fresh-leaf litter samples and occurred with low rates in soil. Our results provide new data in supporting the use of intl1 to detect the environmental health of different land-use systems.

An in silico analysis of acquired antimicrobial resistance genes in Aeromonas plasmids

Sequences of 105 Aeromonas species plasmids were probed for acquired anti-microbial resistance (AMR) genes using a bioinformatics approach. The plasmids showed no positive linear correlation between size and GC content and up to 55 acquired AMR genes were found in 39 (37%) plasmids after in silico screening for resistance against 15 antibiotic drug classes. Overall, potential multiple antibiotic resistance (p-MAR) index ranged from 0.07 to 0.53. Up to 18 plasmids were predicted to mediate multiple drug resistance (MDR). Plasmids pS121-1a (A. salmonicida), pWCX23_1 (A. hydrophila) and pASP-a58 (A. veronii) harboured 18, 15 and 14 AMR genes respectively. The five most occurring drug classes for which AMR genes were detected were aminoglycosides (27%), followed by beta-lactams (17%), sulphonamides (13%), fluoroquinolones (13%), and phenicols (10%). The most prevalent genes were a sulphonamide resistant gene Sul1, the gene aac (6')-Ib-cr (aminoglycoside 6'-N-acetyl transferase type Ib-cr) resistant to aminoglycosides and the blaKPC-2 gene, which encodes carbapenemase-production. Plasmid acquisition of AMR genes was mainly inter-genus rather than intra-genus. Eighteen plasmids showed template or host genes acquired from Pseudomonas monteilii, Salmonella enterica or Escherichia coli. The most occurring antimicrobial resistance determinants (ARDs) were beta-lactamase, followed by aminoglycosides acetyl-transferases, and then efflux pumps. Screening of new isolates in vitro and in vivo is required to ascertain the level of phenotypic expression of colistin and other acquired AMR genes detected.

Temporal effects of repeated application of biogas slurry on soil antibiotic resistance genes and their potential bacterial hosts

Biogas slurry, a liquid end product of animal manure fermentation, is widely used as fertilizer in crop fields. Land application may introduce antibiotics and related resistance genes from livestock production into agricultural soil. Nevertheless, changes in antimicrobial resistance in soil where biogas slurry has been repeatedly applied are not fully understood. In the present study, 13 veterinary antibiotics were analyzed in soils that were repeatedly sprayed with biogas slurry, and simultaneously, temporal changes in antibiotic resistance genes (ARGs) and bacterial community composition were investigated using a real-time quantitative PCR assay and MiSeq sequencing. Long-term repeated application of biogas slurry did not result in excessive accumulation of antibiotic residuals in the soil but increased the abundance of ARGs and facilitated ARG transfer among potential hosts. Although the quantitative PCR assay showed a decreasing trend for the relative abundance of ARGs over time, a relevance network analysis revealed highly complex bacteria-ARG co-occurrence after long-term application, which implied that repeated application might intensify horizontal gene transfer (HGT) of ARGs among different bacterial hosts in soil. The increased relative abundance of the intl1 gene supported the shift in ARG-bacteria co-occurrence. Furthermore, ordination analysis showed that the distributions of antibiotic resistance bacteria (ARB) and ARGs were closely related to application duration than to the influence of antibiotic residuals in the biogas slurry-treated soil environment. Additionally, natural level of ARG abundance in untreated soils indirectly suggested the presence/absence of antibiotics was not a key determinant causing the spread of antimicrobial resistance. This study provides improved insight into the effects of long-term repeated application of biogas slurry on the shift in ARG abundances and bacteria-ARG co-occurrence in soils, highlighting the need to focus on the influence of changed soil environment on the ARG transfer.

Engineering a CRISPR Interference System To Repress a Class 1 Integron in Escherichia coli

Microbial multidrug resistance (MDR) poses a huge threat to human health. Bacterial acquisition of MDR relies primarily on class 1 integron-involved horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs). To date, no strategies other than the use of antibiotics can efficiently cope with MDR. Here, we report that an engineered CRISPR interference (CRISPRi) system can markedly reduce MDR by blocking a class 1 integron in Escherichia coli Using CRISPRi to block plasmid R388 class 1 integron, E. coli recombinants showed halted growth upon exposure to relevant antibiotics. A microplate alamarBlue assay showed that both subgenomic RNAs (sgRNAs) R3 and R6 led to 8- and 32-fold decreases in half-maximal inhibitory concentrations (IC50) for trimethoprim and sulfamethoxazole, respectively. Reverse transcription and quantitative PCR (RT-qPCR) revealed that the strain employing sgRNA R6 exhibited 97% and 84% decreases in the transcriptional levels of the dfrB2 cassette and sul1, two typical ARGs, respectively. RT-qPCR analysis also demonstrated that the strain recruiting sgRNA R3 showed a 96% decrease in the transcriptional level of intI1, and a conjugation assay revealed a 1,000-fold decrease in HGT rates of ARGs. Overall, the sgRNA R3 targeting the 31 bp downstream of the Pc promoter on the intI1 nontemplate strand outperformed other sgRNAs in reducing integron activity. Furthermore, this CRISPRi system is reversible, genetically stable, and titratable by varying the concentration of the inducer. To our knowledge, this is the first report on exploiting a CRISPRi system to reduce the class 1 integron in E. coli This study provides valuable insights for future development of CRISPRi-based antimicrobial agents and cellular therapy to suppress MDR.

Profiles of antibiotic resistome with animal manure application in black soils of northeast China

Black soils (Mollisols) are important soil resources for crop production and maintain food safety in China. For keeping soil fertility, the application of animal manure is commonly practiced in black soils. However, the impact of this application on abundance and diversity of antibiotic resistance genes (ARGs) in black soils of China remains unclear. Here, we surveyed the profiles of ARGs in 72 soil samples collected from four long-term experimental stations with different fertilization regimes and from open farmlands in two sites across northeast China using high-throughput quantitative PCR. Results showed that a total of 178 ARGs including mobile genetic elements (MGEs) were detected, and the diversity and abundance of ARGs were significantly increased with manure application. Additionally, the finding of a significant positive correlation between relative abundance of ARGs and MGEs (P <  0.0001), suggesting that horizontal gene transfer may potentially impact the transmission of ARGs. Furthermore, two genes aadA-1-01 and mexF, encoding resistance to aminoglycoside and multidrug, respectively, were recognized as indicators to estimate the abundance of other co-occurring ARGs. These findings provided insights into the soil resistome in black soils of northeast China and also highlighted the environmental risks caused by manure application should not be ignored.

Molecular epidemiology of clinically high-risk Pseudomonas aeruginosa strains: Practical overview

In recent years, numerous outbreaks of multidrug-resistant Pseudomonas aeruginosa have been reported across the world. Once an outbreak occurs, besides routinely testing isolates for susceptibility to antimicrobials, it is required to check their virulence genotypes and clonality profiles. Replacing pulsed-field gel electrophoresis DNA fingerprinting are faster, easier-to-use, and less expensive polymerase chain reaction (PCR)-based methods for characterizing hospital isolates. P. aeruginosa possesses a mosaic genome structure and a highly conserved core genome displaying low sequence diversity and a highly variable accessory genome that communicates with other Pseudomonas species via horizontal gene transfer. Multiple-locus variable-number tandem-repeat analysis and multilocus sequence typing methods allow for phylogenetic analysis of isolates by PCR amplification of target genes with the support of Internet-based services. The target genes located in the core genome regions usually contain low-frequency mutations, allowing the resulting phylogenetic trees to infer evolutionary processes. The multiplex PCR-based open reading frame typing (POT) method, integron PCR, and exoenzyme genotyping can determine a genotype by PCR amplifying a specific insertion gene in the accessory genome region using a single or a multiple primer set. Thus, analyzing P. aeruginosa isolates for their clonality, virulence factors, and resistance characteristics is achievable by combining the clonality evaluation of the core genome based on multiple-locus targeting methods with other methods that can identify specific virulence and antimicrobial genes. Software packages such as eBURST, R, and Dendroscope, which are powerful tools for phylogenetic analyses, enable researchers and clinicians to visualize clonality associations in clinical isolates.

Comprehensive Understanding of the Plasmid-Mediated Colistin Resistance Gene mcr-1 in Aquatic Environments

The emergence of plasmid-mediated colistin resistance gene mcr-1 has attracted global attention and raised serious concerns about its possible cross-environment dissemination. However, the systematic exploration of mcr-1 both by monitoring and genetic dissection in aquatic environments has not been conducted. This study addresses the gap related to the occurrence and distribution of mcr-1 in watersheds, eastern China. The results showed an abundance of mcr-1 gene in four watersheds, and the highest level of mcr-1 reached 1.8 × 10⁹ gene copies per liter of water. Furthermore, the transfer frequencies of the plasmids in isolated Escherichia coli were 2.76 × 10^-6-6.11 × 10^-4 within genera and minimal inhibitory concentrations of polymyxin resistance were 8-16 mg/L for transconjugants. Mass spectrometry data allowed visualization of the function of mcr-1 expression, rendering bacterial resistance to colistin. The genetic details of six mcr-1-harboring plasmids in E. coli isolates of aquatic origin were obtained by single-molecule real-time sequencing. These plasmids were closely associated with E. coli strains of pig and human origin, supporting the concept of mcr-1 dissemination across natural environments, livestock farms, and humans. In conclusion, this study provides the first glimpse of the profile of mcr-1-harboring plasmids and their genetic environment in aquatic ecosystems.

Clinical class 1 integron-integrase gene - A promising indicator to monitor the abundance and elimination of antibiotic resistance genes in an urban wastewater treatment plant

In this study, 295 antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) from the influent, activated sludge (AS), and membrane bioreactor (MBR) permeate were primarily examined in the wastewater treatment plant (WWTP) biweekly over 13 months. The absolute concentrations of ARGs and MGEs respectively ranged from 1.27 × 10¹⁰ to 1.94 × 10¹¹ and 8.00 × 10⁹ to 1.24 × 10¹¹ copies/L in the influent, of which were reduced by 2 to 3 orders of magnitude in the permeate. No significant seasonal variation of ARGs and MGEs was found in the WWTP, except that the absolute abundance of ARGs and MGEs in the AS was peaked during spring. The antibiotics affected neither ARGs nor MGEs significantly, suggesting their concentrations may be not high enough to pose a selective pressure. In contrast, the bacterial community had direct effect on the MGEs variation, meanwhile the MGEs influenced the ARG abundance directly. Class 1 integron-integrase gene (intI1), clinical intI1, and Tn21 associated more frequently with ARGs in the AS over long-term, suggesting the potential of them involved in horizontal gene transfer. Both intI1 and clinical intI1 had significantly positive associations with the overall abundance of ARGs, as well as significantly negative relationships with the overall removal rates of ARGs in the MBR. However, the abundances between intI1 and clinical intI1 were significantly different. Meanwhile, clinical intI1 remained rather consistent proportion with the ARG abundance in the AS and permeate, was stronger correlated with human pathogens, and was associated with greater number of ARGs over time. Moreover, clinical intI1 was significantly associated with the removal efficiency of ARGs from all classes. Taken together, clinical intI1 can be adopted as an indicator for the abundance and removal efficiency of ARGs in the WWTP.

Estuarine sediments are key hotspots of intracellular and extracellular antibiotic resistance genes: A high-throughput analysis in Haihe Estuary in China

Estuaries lie between terrestrial/freshwater and marine ecosystems, receive considerable pollutant input from land-based sources, and are considerably influenced by human activities. However, little attention has been paid to combined research on extracellular antibiotic resistance genes (eARGs) and intracellular ARGs (iARGs) in the estuarine environment. In this study, we profiled eARGs and iARGs in sediments from Haihe Estuary, China by adopting high-throughput quantitative PCR and investigated their relationship with mobile genetic elements (MGEs), the bacterial community and environmental factors. The results showed that the abundance of eARGs ranged from 9.06 × 10⁶ to 1.32 × 10⁸ copies/g and that of iARGs ranged from 3.31 × 10⁷ to 2.93 × 10⁸ copies/g, indicating that estuarine sediments were key hotspots of eARGs and iARGs. Additionally, multidrug resistance genes were both highly diverse and abundant in Haihe Estuary, especially in coastal samples. The high abundance of vancomycin and carbapenemase resistance genes may pose a potential health risk to human. Salinity altered the composition and structure of the bacterial community. Partial redundancy analysis showed that the bacterial community and MGEs appeared to be the major drivers of ARG variance in estuarine sediment. This study provides an overview of the distribution of eARG and iARG along the Haihe Estuary and draws attention to the need to control pollutants in estuary ecosystems.

Antimicrobial Resistance and Food Animals: Influence of Livestock Environment on the Emergence and Dissemination of Antimicrobial Resistance

The emergence and dissemination of antimicrobial resistance among human, animal and zoonotic pathogens pose an enormous threat to human health worldwide. The use of antibiotics in human and veterinary medicine, and especially the use of large quantities of antibiotics in livestock for the purpose of growth promotion of food animals is believed to be contributing to the modern trend of the emergence and spread of bacteria with antibiotic resistant traits. To better control the emergence and spread of antimicrobial resistance several countries from Western Europe implemented a ban for antibiotic use in livestock, specifically the use of antibiotics for growth promotion of food animals. This review article summarizes the recent knowledge of molecular acquisition of antimicrobial resistance and the effects of implementation of antibiotic growth promoter bans on the spread of antimicrobial resistant bacteria in animals and humans. In this article, we also discuss the main zoonotic transmission routes of antimicrobial resistance and novel approaches designed to prevent or slow down the emergence and spread of antimicrobial resistance worldwide. Finally, we provide future perspectives associated with the control and management of the emergence and spread of antimicrobial resistant bacteria.

Molecular diversity of extended-spectrum β-lactamases and carbapenemases, and antimicrobial resistance

Along with the recent spread of multidrug-resistant bacteria, outbreaks of extended-spectrum β-lactamase (ESBL) and carbapenemase-producing bacteria present a serious challenge to clinicians. β-lactam antibiotics are the most frequently used antibacterial agents and ESBLs, and carbapenemases confer resistance not only to carbapenem antibiotics but also to penicillin and cephem antibiotics. The mechanism of β-lactam resistance involves an efflux pump, reduced permeability, altered transpeptidases, and inactivation by β-lactamases. Horizontal gene transfer is the most common mechanism associated with the spread of extended-spectrum β-lactam- and carbapenem resistance among pathogenic bacterial species. Along with the increase in antimicrobial resistance, many different types of ESBLs and carbapenemases have emerged with different enzymatic characteristics. For example, carbapenemases are represented across classes A to D of the Ambler classification system. Because bacteria harboring different types of ESBLs and carbapenemases require specific therapeutic strategies, it is essential for clinicians to understand the characteristics of infecting pathogens. In this review, we summarize the current knowledge on carbapenem resistance by ESBLs and carbapenemases, such as class A carbapenemases, class C extended-spectrum AmpC (ESAC), carbapenem-hydrolyzing class D β-lactamases (CHDLs), and class B metallo-β-lactamases, with the aim of aiding critical care clinicians in their therapeutic decision making.

The Peril and Promise of Integrons: Beyond Antibiotic Resistance

Integrons are bacterial genetic elements that can capture, rearrange, and express mobile gene cassettes. They are best known for their role in disseminating antibiotic-resistance genes among pathogens. Their ability to rapidly spread resistance phenotypes makes it important to consider what other integron-mediated traits might impact human health in the future, such as increased virulence, pathogenicity, or resistance to novel antimicrobial strategies. Exploring the functional diversity of cassettes and understanding their de novo creation will allow better pre-emptive management of bacterial growth, while also facilitating development of technologies that could harness integron activity. If we can control integrons and cassette formation, we could use integrons as a platform for enzyme discovery and to construct novel biochemical pathways, with applications in bioremediation or biosynthesis of industrial and therapeutic molecules. Integron activity thus holds both peril and promise for humans.

Identification of antimicrobial resistant bacteria from plant-based food products imported into Canada

The role of plant-based foods in the epidemiology of antimicrobial resistance has been inadequately studied. In this investigation, resistant organisms from vegetables, fruits and spices imported into Canada were identified and characterized. A total of 143 products imported from primarily Asian and African countries were purchased from international markets in Saskatoon, Saskatchewan. Samples were selectively cultured for bacterial species where resistance is known to be emerging. The proportions of samples positive for each organism were as follows: E. coli (n = 13, 9.1%), Salmonella spp. (n = 2, 1.4%), ESBL producing Enterobacter spp. (n = 2, 1.4%) and K. pneumoniae (n = 2, 1.4%), S. aureus (n = 7, 4.9%) and Enterococcus spp. (n = 66, 46.2%). Antimicrobial minimum inhibitory concentrations were determined by broth micro-dilution and agar-dilution. Based on the susceptibility of each organism, isolates were screened for resistance genes (β-lactamases and plasmid mediated quinolones resistance determinants) by PCR. Extended-spectrum β-lactamase producing Enterobacteriaceae and methicillin resistant S. aureus (MRSA) were identified from 6/143 (4.2%) and 2/143 (1.4%) of samples respectively. The qnrB, qnrS and aac(6')-Ib-cr plasmid mediated quinolone resistance determinants were identified in 2/143 (1.4%) of samples tested. None of the Enterobacteriaceae isolates were resistant to meropenem or colistin. Similarly, all Enterococcus isolates remained susceptible to ampicillin, penicillin and vancomycin. Finding multi-drug resistant bacteria which are frequently isolated from human infections is concerning, although the contribution of the global food trade to the dissemination of resistance remains cryptic. These results suggest that imported plant-based foods may be an underappreciated source of clinically relevant resistant organisms. Further study is required to address these gaps in our understanding of the epidemiology of resistance, and the magnitude of the risk posed to human health by these organisms.

Small-scale wastewater treatment plants as a source of the dissemination of antibiotic resistance genes in the aquatic environment

Wastewater treatment plants (WWTPs) are significant source of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs), which can spread further in the environment by reaching rivers together with effluents discharged from WWTPs. In this study untreated and treated wastewater (UWW, TWW), upstream and downstream river water (URW, DRW) were collected from 4 WWTPs, in the winter and autumn seasons. The occurrence of ARB resistant to beta-lactams and tetracyclines as well as the presence of antibiotics from these classes were analysed in water and wastewater samples. Additionally, the amounts of 12 ARGs, 2 genes of mobile genetic elements (MGEs), gene uidA identifying E. coli and 16S rRNA were also determined. Resistance to beta-lactams prevailed among ARB in water and wastewater samples (constituting 82-88% of total counts of bacteria). The dominant genes in water and wastewater samples were bla_TEM, tetA, sul1. The gene bla_OXA demonstrated high variability of its concentration in samples collected in both seasons. Despite the high per cent reduction of ARB and ARGs concentration observed during the wastewater treatment processes, their large quantities are still transmitted into the environment. The research focuses on WWTPs' role in the dissemination of ARGs and MGEs in the aquatic environment.

Antibiotic resistance: bioinformatics-based understanding as a functional strategy for drug design

The use of antibiotics to manage infectious diseases dates back to ancient civilization, but the lack of a clear distinction between the therapeutic and toxic dose has been a major challenge. This precipitates the notion that antibiotic resistance was from time immemorial, principally because of a lack of adequate knowledge of therapeutic doses and continuous exposure of these bacteria to suboptimal plasma concentration of antibiotics. With the discovery of penicillin by Alexander Fleming in 1924, a milestone in bacterial infections' treatment was achieved. This forms the foundation for the modern era of antibiotic drugs. Antibiotics such as penicillins, cephalosporins, quinolones, tetracycline, macrolides, sulphonamides, aminoglycosides and glycopeptides are the mainstay in managing severe bacterial infections, but resistant strains of bacteria have emerged and hampered the progress of research in this field. Recently, new approaches to research involving bacteria resistance to antibiotics have appeared; these involve combining the molecular understanding of bacteria systems with the knowledge of bioinformatics. Consequently, many molecules have been developed to curb resistance associated with different bacterial infections. However, because of increased emphasis on the clinical relevance of antibiotics, the synergy between in silico study and in vivo study is well cemented and this facilitates the discovery of potent antibiotics. In this review, we seek to give an overview of earlier reviews and molecular and structural understanding of bacteria resistance to antibiotics, while focusing on the recent bioinformatics approach to antibacterial drug discovery.

Understanding the evolution of antibiotic resistance at the molecular level as a functional tool for bioinformatic-based drug design.

Investigation of Integron-Associated Resistance Gene Cassettes in Urinary Isolates of Klebsiella pneumoniae in Yasuj, Southwestern Iran During 2015-16

BACKGROUND

Growing antibiotic resistance among urinary opportunistic pathogens such as Klebsiella pneumoniae (K. pneumonia) has created a worrisome condition in the treatment of the Urinary Tract Infections (UTIs) in recent years. Integrons play a significant role in the dissemination of antibiotic resistance genes. The present study was conducted to investigate class 1-3 integrons and the corresponding resistance gene cassettes in urinary K. pneumoniae isolates.

METHODS

In this study, from December 2015 to September 2016, a total of 196 K. pneumoniae isolates were collected from the patients with UTI referred to medical diagnostic laboratories in Yasouj, Southwestern Iran. Antibiotic susceptibility patterns of isolates were determined using 12 antibiotics by the disc diffusion method. Polymerase Chain Reaction (PCR) was used for detection of integron genes (intI1, intI2, and intI3). The variable regions of integrons were amplified by PCR and sequenced to identify the corresponding gene cassettes.

RESULTS

Thirty-nine different antibiotic resistance profiles were observed among K. pneumoniae isolates. Only 12.2% of K. pneumoniae isolates were found to harbor the intI1 gene. While 17 (60.7%) out of 28 Multidrug Resistance (MDR) K. pneumoniae isolates carried the intI1 gene, only 4.2% of non-MDR isolates harbored intI1 gene. Totally 7 different gene cassette arrays were found in the intI1 gene of K. pneumoniae isolates. The aadA1 was the most prominent gene cassette. Also, high frequency of dfrA containing gene cassettes was observed.

CONCLUSION

Continuous monitoring and characterization of integrons and their associated gene cassettes could be helpful in controlling the rising rate of antibiotic resistance.

Molecular surveillance of carbapenemase-producing Pseudomonas aeruginosa at three medical centres in Cologne, Germany

Background

Pseudomonas aeruginosa is a common pathogen causing hospital-acquired infections. Carbapenem resistance in P. aeruginosa is either mediated via a combination of efflux pumps, AmpC overexpression, and porin loss, or through an acquired carbapenemase. Carbapenemase-producing P. aeruginosa (CPPA) strains are known to cause outbreaks and harbour a reservoir of mobile antibiotic resistance genes, however, few molecular surveillance data is available. The aim of this study was to analyse the prevalence and epidemiology of CPPA in three German medical centres from 2015 to 2017.

Methods

Identification and susceptibility testing were performed with VITEK 2 system. P. aeruginosa non-susceptible to piperacillin, ceftazidime, cefepime, imipenem, meropenem and ciprofloxacin (4MRGN according to the German classification guideline) isolated from 2015 to 2017 were analysed. A two-step algorithm to detect carbapenemases was performed: phenotypic tests (EDTA- and cloxacillin-combined disk tests) followed by PCR, Sanger sequencing, and eventually whole genome sequencing. CPPA isolates were further genotyped by RAPD and PFGE. In-hospital transmission was investigated using conventional epidemiology.

Results

Sixty two P. aeruginosa isolates were available for further analysis, of which 21 were CPPA as follows: bla_VIM-1 (n = 2), bla_VIM-2 (n = 17), bla_NDM-1/bla_GES-5 (n = 1) and the newly described bla_IMP-82 (n = 1). CPPA were mostly hospital-acquired (71.4%) and isolated on intensive care units (66.7%). All (except one) were from the tertiary care centre. PFGE typing revealed one large cluster of VIM-2-producing CPPA containing 13 isolates. However, using conventional epidemiology, we were only able to confirm three patient-to-patient transmissions, and one room-to-patient transmission, on several intensive care units.

Conclusions

These data give insight into the epidemiology of CPPA in three centres in Germany over a period of 3 years. Carbapenemases are a relevant resistance mechanism in 4MRGN-P. aeruginosa, illustrated by genetically related VIM-2-producing strains that seem to be endemic in this region. Our data suggest that infection control measures should especially focus on controlling transmission on the ICU and support the need for a local molecular surveillance system.

Freshwater salmon aquaculture in Chile and transferable antimicrobial resistance

Large amounts of antimicrobials are used in salmonid aquaculture in Chile. Most are used in marine aquaculture, but appreciable amounts are also employed in freshwater aquaculture. Much research and many publications have examined transferable antimicrobial resistance in bacteria isolated from marine salmon farms, but much less attention has been paid to this area in freshwater salmon farming. A recent paper by Domínguez et al. (2019) has as least in part remedied this situation. We now comment on some of its interpretations and have attempted to point out its areas of strength and weakness in light of the published scientific literature. Seen in this setting, the important results presented by Domínguez et al. (2019) underline the need for increased awareness of the challenge to animal and human health posed by excessive use of antimicrobials in aquaculture.

Association of phylogenetic distribution and presence of integrons with multidrug resistance in Escherichia coli clinical isolates from children with diarrhoea

BACKGROUND

Escherichia coli strains include both commensal and virulent clones distributed in different phylogenetic groups. Antimicrobial resistance is an increasingly serious public health threat at the global level and integrons are important mobile genetic elements involved in resistance dissemination. This paper aims to determine the phylogenetic groups and presence of class 1 (intl1) and 2 (intl2) integrons in E. coli clinical isolates from children with diarrhoea, and to associate these characteristics with their antimicrobial resistance.

METHODS

Phylogeny and presence of integrons (intl1 and intl2) were analysed by PCR and amplicon sequencing in 70 E. coli isolates from children with and without diarrhoea (35 of each group) from Sinaloa, Mexico; these variables were analysed for correlation with the antimicrobial resistance profile of the isolates.

RESULTS

The most frequent phylogroups were A (42.9%) and B2 (15.7%). The E. coli isolates from children with diarrhoea were distributed in all phylogroups; while strains from children without diarrhoea were absent from phylogroups C, E, and clade I. The 17.1% of the isolates carried integrons (15.7% intI1 and 1.4% intI2); 28.6% of the isolates from children with diarrhoea showed the class 1 integron. Strains of phylogroup A showed the highest frequency of integrons (33.3%). The association of multidrug resistance and the presence of integrons was identified in 58.3% of strains isolated from children with diarrhoea included in phylogroups A and B2. The sequence analysis of intl1 and intl2 showed silent point mutations and similarities with plasmids of some APEC and AIEC strains.

CONCLUSION

Commensal E. coli strains are potential disseminators of antimicrobial resistance, and the improvement in the use of antimicrobials to treat childhood diarrhoea is essential for the control of such resistance.

Molecular Characteristics of GES-Type Carbapenemase-Producing Pseudomonas aeruginosa Clinical Isolates from Long-Term Care Facilities and General Hospitals in South Korea

Since carbapenems have been used for the treatment of infections in medical settings, multidrug-resistant Pseudomonas aeruginosa containing resistance for carbapenems has become a major cause of nosocomial infections worldwide. Information on carbapenemase-producing P. aeruginosa isolates at community hospitals, including long-term care facilities and general hospitals, has rarely been reported in South Korea. The aims of this study were to describe the characteristics of seven carbapenemase-producing P. aeruginosa isolates recovered from two long-term care facilities in South Korea. The carbapenemase genes were identified by PCR and sequencing. Strain typing was assessed by pulsed field gel electrophoresis and multilocus sequence typing (MLST) analysis. Isolates with a genomic island and class I integron surrounding bla_GES-type were confirmed by the PCR mapping method. Of seven GES-type carbapenemase-producing P. aeruginosa isolates, the bla_GES-24 gene was detected in six isolates, and the bla_GES-5 gene was detected in one isolate. The epidemiological relatedness of the seven isolates carrying bla_GES-24 and bla_GES-5 showed >81% similarity. Five isolates carrying bla_GES-24 were sequence type 155 (ST155) by MLST, followed by one ST244 isolate carrying bla_GES-24 and one ST308 isolate carrying bla_GES-5. bla_GES-type genes were embedded in two different class I integrons in a genomic island-15-like region. Our results indicate the possible spread of carbapenemase-producing P. aeruginosa and present a current threat of antimicrobial resistance in community hospitals.

Implications of Mobile Genetic Elements for Salmonella enterica Single-Nucleotide Polymorphism Subtyping and Source Tracking Investigations

Single-nucleotide polymorphisms (SNPs) are widely used for whole-genome sequencing (WGS)-based subtyping of foodborne pathogens in outbreak and source tracking investigations. Mobile genetic elements (MGEs) are commonly present in bacterial genomes and may affect SNP subtyping results if their evolutionary history and dynamics differ from that of the bacterial chromosomes. Using Salmonella enterica as a model organism, we surveyed major categories of MGEs, including plasmids, phages, insertion sequences, integrons, and integrative and conjugative elements (ICEs), in 990 genomes representing 21 major serotypes of S. enterica We evaluated whether plasmids and chromosomal MGEs affect SNP subtyping with 9 outbreak clusters of different serotypes found in the United States in 2018. The median total length of chromosomal MGEs accounted for 2.5% of a typical S. enterica chromosome. Of the 990 analyzed S. enterica isolates, 68.9% contained at least one assembled plasmid sequence. The median total length of assembled plasmids in these isolates was 93,671 bp. Plasmids that carry high densities of SNPs were found to substantially affect both SNP phylogenies and SNP distances among closely related isolates if they were present in the reference genome for SNP subtyping. In comparison, chromosomal MGEs were found to have limited impact on SNP subtyping. We recommend the identification of plasmid sequences in the reference genome and the exclusion of plasmid-borne SNPs from SNP subtyping analysis.IMPORTANCE Despite increasingly routine use of WGS and SNP subtyping in outbreak and source tracking investigations, whether and how MGEs affect SNP subtyping has not been thoroughly investigated. Besides chromosomal MGEs, plasmids are frequently entangled in draft genome assemblies and yet to be assessed for their impact on SNP subtyping. This study provides evidence-based guidance on the treatment of MGEs in SNP analysis for Salmonella to infer phylogenetic relationship and SNP distance between isolates.

Class 1 integrons as predominant carriers in Escherichia coli isolates from waterfowls in Hainan, China

This study was conducted to determine the prevalence of integrons and associated gene cassettes in Escherichia coli (E. coli) isolates from waterfowls in Hainan, China. The antimicrobial resistance profile of the isolates was examined by using disc diffusion test. In addition, PCR, RFLP, plasmid replicon typing and DNA sequencing analyses were used for the characterization of integrase genes (class 1, 2 and 3) and associated gene cassettes. Approximatively, 90% of the isolates were positive for the integrase genes by PCR. Specifically, class 1 and class 2 integrons were found in 252 (81%) and 7 (2.3%) strains, respectively. While 21 (6.7%) isolates were positive for both class 1 and class 2 integrons. However, none of the isolate was positive for the class 3 integrons. In addition, 5 various cassette arrays, dfrA1-orfC, aadA2, aadA1, dfrA1-aadA1, and dfrA1-orfC- aadA1, were found within the variable regions (VRs) of class 1 integron isolates. While only single cassette array, dfrA1-sat2- aadA1, was identified within VRs of class 2 integron isolates. We identified incF plasmid as the most common plasmid type, which was detected in 81 of 243 VRs containing isolates. This study is the first report showing the baseline characteristics of integrons in E. coli isolates from waterfowls in Hainan, China. Our results provide evidence of the waterfowl birds as a reservoir of class 1 and class 2 integrons carrying antibiotic resistance gene cassettes. Therefore, strict preventive measures should be taken to avoid the spread of mobile genetic resistance elements in waterfowls in China.

Molecular Detection Of Multidrug-Resistant Salmonella Isolated From Livestock Production Systems In South Africa

BACKGROUND

Antibiotic-resistant bacterial pathogens associated with livestock remain a major concern worldwide as they get transmitted from animals to humans and cause foodborne and zoonotic diseases.

METHODS

Antimicrobial resistance in livestock-associated Salmonella spp in South Africa was investigated using molecular DNA methods. Three hundred and sixty-one environmental faecal samples were randomly collected from avian (chicken and ducks), cows, pigs, goats, and sheep. Salmonella spp. were isolated on selective media and were confirmed using the polymerase chain reaction. Antimicrobial susceptibility testing against ampicillin, chloramphenicol, ciprofloxacin, ceftriaxone, azithromycin, tetracycline, amoxicillin-clavulanate and trimethoprim-sulfamethoxazole was determined using the Kirby-Bauer disk diffusion method. Isolates were screened for the presence of blaTEM-1, blaCMY-2, tetA, tetC, sul2 and dfrA7 resistance genes by PCR.

RESULTS

Most of the isolates were resistant to ampicillin (64%), tetracycline (63%), amoxicillin-clavulanate (49%), trimethoprim-sulfamethoxazole (38%), and ceftriaxone (20%). Eight percent of the tested isolates were ciprofloxacin-resistant Salmonella spp. Multidrug resistance was observed with the mean multiple antibiotic resistance (MAR) index of 0.31. The study demonstrated that 43% of the isolates were multiple drug resistant. The prevalence rates of resistance genes were 44% for blaTEM-1 , 35% for blaCMY-2 , 21% for sul2, 18% for tetC, 14% for dfrA7 and 8% for tetA.

CONCLUSION

Resistance to ceftriaxone, detection of blaCMY-2 gene and the high level of intermediate susceptibility (33%) against ciprofloxacin suggested that livestock carry problematic Salmonella spp. This study used the global one-health initiative to report the potential public health risks of livestock-associated pathogens and highlights the importance of monitoring the trends of antimicrobial resistance for sustainability of antibiotics.

Carbapenemase and ESBL genes with class 1 integron among fermenting and nonfermenting bacteria isolated from water sources from India

The present study was aimed to detect the carbapenemase, extended-spectrum β-lactamase (ESBL), and intI1 gene of class 1 integron among fermenting (n = 61) and nonfermenting (n = 10) bacterial isolates recovered from water samples (n = 128). Isolates were identified by 16S rRNA sequencing. These isolates showed reduced-susceptibility to third-generation cephalosporins and carbapenems. The isolates varied in number and size of plasmids (2 kb to >20 kb). Plasmid DNA screening showed 5·6, 7, 11·2 and 26·7% prevalence of bla_KPC , bla_NDM , bla_SHV and bla_TEM genes respectively. Diverse bla_NDM (bla_NDM-1 and bla_NDM-4 ) and bla_SHV subtypes (bla_SHV-2 and bla_SHV-11 ) were recorded, unlike the single allelic bla_KPC (bla_KPC-2 ) and bla_TEM (bla_TEM-1 ) gene. Of the total 27 bla-gene-producing bacterial isolates, seven isolates co-harboured the carbapenemase genes (bla_NDM or bla_KPC or the both) along with the ESBL genes (bla_SHV or bla_TEM ). The intI1 gene of class 1 integron was detected among 12 (44·4%) of ESBL- and/or carbapenemase-harbouring isolates. Gene transferability was seen among four of the 10 Enterobacteriaceae donors. Carbapenemases and ESBLs with class 1 integron among aquatic environmental isolates raise the serious issue of the biosecurity and health of the ecosystem. SIGNIFICANCE AND IMPACT OF THE STUDY: Anthropologically affected and polluted environment harbours the resistance threats, where a diverse bacterial species maintain, develop and exchange genetic determinants that constitute a risk to human and ecological health. The antimicrobial resistance (AMR) in Enterobacteriaceae and non-Enterobacteriaceae bacteria caused the failure of the therapy of last resort (carbapenems) and thus lead to life-threatening infections affecting public health. Surveillance and monitoring of AMR could be important for epidemiological, diagnostic testing and control of pathogens. This is a point-prevalence study reporting the comparative occurrence and co-occurrence of carbapenemase and extended-spectrum β-lactamase genes among fermenting and nonfermenting bacteria isolated from the aquatic environment in India.