Novel insights into the co-selection of metal-driven antibiotic resistance in bacteria: a study of arsenic and antibiotic co-exposure. - Related Documents




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678601.0000Novel insights into the co-selection of metal-driven antibiotic resistance in bacteria: a study of arsenic and antibiotic co-exposure. The simultaneous development of antibiotic resistance in bacteria due to metal exposure poses a significant threat to the environment and human health. This study explored how exposure to both arsenic and antibiotics affects the ability of an arsenite oxidizer, Achromobacter xylosoxidans CAW4, to transform arsenite and its antibiotic resistance patterns. The bacterium was isolated from arsenic-contaminated groundwater in the Chandpur district of Bangladesh. We determined the minimum inhibitory concentration (MIC) of arsenite, cefotaxime, and tetracycline for A. xylosoxidans CAW4, demonstrating a multidrug resistance (MDR) trait. Following this determination, we aimed to mimic an environment where A. xylosoxidans CAW4 was exposed to both arsenite and antibiotics. We enabled the strain to grow in sub-MIC concentrations of 1 mM arsenite, 40 µg/mL cefotaxime, and 20 µg/mL tetracycline. The expression dynamics of the arsenite oxidase (aioA) gene in the presence or absence of antibiotics were analyzed. The findings indicated that simultaneous exposure to arsenite and antibiotics adversely affected the bacteria's capacity to metabolize arsenic. However, when arsenite was present in antibiotics-containing media, it promoted bacterial growth. The study observed a global downregulation of the aioA gene in arsenic-antibiotic conditions, indicating the possibility of increased susceptibility through co-resistance across the entire bacterial population of the environment. This study interprets that bacterial arsenic-metabolizing ability can rescue the bacteria from antibiotic stress, further disseminating environmental cross-resistance. Therefore, the co-selection of metal-driven antibiotic resistance in bacteria highlights the need for effective measures to address this emerging threat to human health and the environment.202438538852
675410.9997Real-time PCR based analysis of metal resistance genes in metal resistant Pseudomonas aeruginosa strain J007. A uranium (U)-resistant and -accumulating Pseudomonas aeruginosa strain was characterized to assess the response of toxic metals toward its growth and expression of metal resistance determinants. The bacterium showed MIC (minimum inhibitory concentration) values of 6, 3, and 2 mM for Zn, Cu, and Cd, respectively; with resistance phenotype conferred by periplasmic Cu sequestering copA and RND type heavy metal efflux czcA genes. Real-time PCR-based expression analysis revealed significant upregulation of both these genes upon exposure to low concentrations of metals for short duration, whereas the global stress response gene sodA encoding superoxide dismutase enzyme was upregulated only at higher metal concentrations or longer exposure time. It could also be inferred that copA and czcA are involved in providing resistance only at low metal concentrations, whereas involvement of "global stress response" phenomenon (expression of sodA) at higher metal concentration or increased exposure was evident. This study provides significant understanding of the adaptive response of bacteria surviving in metal and radionuclide contaminated environments along with the development of real-time PCR-based quantification method of using metal resistance genes as biomarker for monitoring relevant bacteria in such habitats.201626662317
372920.9997Sub-inhibitory gentamicin pollution induces gentamicin resistance gene integration in class 1 integrons in the environment. Antibiotics at sub-inhibitory concentrations are often found in the environment. Here they could impose selective pressure on bacteria, leading to the selection and dissemination of antibiotic resistance, despite being under the inhibitory threshold. The goal of this study was to evaluate the effects of sub-inhibitory concentrations of gentamicin on environmental class 1 integron cassettes in natural river microbial communities. Gentamicin at sub-inhibitory concentrations promoted the integration and selection of gentamicin resistance genes (GmRG) in class 1 integrons after only a one-day exposure. Therefore, sub-inhibitory concentrations of gentamicin induced integron rearrangements, increasing the mobilization potential of gentamicin resistance genes and potentially increasing their dissemination in the environment. This study demonstrates the effects of antibiotics at sub-inhibitory concentrations in the environment and supports concerns about antibiotics as emerging pollutants.202337244902
610930.9996Studies on arsenic transforming groundwater bacteria and their role in arsenic release from subsurface sediment. Ten different Gram-negative arsenic (As)-resistant and As-transforming bacteria isolated from As-rich groundwater of West Bengal were characterized to assess their role in As mobilization. 16S rRNA gene analysis confirmed the affiliation of these bacteria to genera Achromobacter, Brevundimonas, Rhizobium, Ochrobactrum, and Pseudoxanthomonas. Along with superior As-resistance and As-transformation abilities, the isolates showed broad metabolic capacity in terms of utilizing a variety of electron donors and acceptors (including As) under aerobic and anaerobic conditions, respectively. Arsenic transformation studies performed under various conditions indicated highly efficient As(3+) oxidation or As(5+) reduction kinetics. Genes encoding As(3+) oxidase (aioA), cytosolic As(5+) reductase (arsC), and As(3+) efflux pump (arsB and acr3) were detected within the test isolates. Sequence analyses suggested that As homeostasis genes (particularly arsC, arsB, and acr3) were acquired by most of the bacteria through horizontal gene transfer. A strong correlation between As resistance phenotype and the presence of As(3+) transporter genes was observed. Microcosm study showed that bacterial strain having cytosolic As(5+) reductase property could play important role in mobilizing As (as As(3+)) from subsurface sediment.201424764001
451040.9996Environmental concentrations of antibiotics, biocides, and heavy metals fail to induce phenotypic antimicrobial resistance in Escherichia coli. Most anthropogenically affected environments contain mixtures of pollutants from different sources. The impact of these pollutants is usually the combined effect of the individual polluting constituents. However, how these stressors contribute to the development of antimicrobial resistance in environmental microorganisms is poorly understood. Thus, a 30-day exposure experiment to environmental and sub-inhibitory concentrations of oxytetracycline, amoxicillin, zinc, copper, BAC (benzalkonium chloride) 10 and DADMAC (diallyldimethylammonium chloride) 12, was conducted using fully susceptible E. coli ATCC 25922 to ascertain any development of phenotypic or genotypic resistance. Furthermore, wild-type isolates were collected from the same aquatic environment as the stressors, analysed for phenotypic resistance using the disk diffusion method and genotypically through whole genome sequencing. Exposure to the various concentrations and combinations of the stressors did not trigger phenotypic resistance in the experimental bacteria. Furthermore, genotypic analysis of the WGS on the exposed isolates only found the macrolide resistance mdf(A) gene (also present in the control strain) and the disinfectant resistance gene sitABCD. With further analysis for single nucleotide variants (SNV), mutations were detected for 19 genes that encoded for oxidative stress, DNA repair, membrane proteins efflux systems, growth and persister formations except for the robA, a transcription protein subset of the ArcC/XylS family of proteins, which confer multidrug resistance in E. coli. This indicates that exposure to sub-inhibitory concentrations of antibiotics, heavy metals and biocide residues in the aquatic environmental concentrations of the stressors identified in the current study could not induce phenotypic or genotypic resistance but encoded for genes responsible for the development of persistence and tolerance in bacteria, which could be a precursor to the development of resistance in environmental bacteria.202337482346
677550.9996Copper nanoparticles and copper ions promote horizontal transfer of plasmid-mediated multi-antibiotic resistance genes across bacterial genera. The spread of antibiotic resistance has become a major concern for public health. As emerging contaminants, various metallic nanoparticles (NPs) and ionic heavy metals have been ubiquitously detected in various environments. Although previous studies have indicated NPs and ionic heavy metals could exhibit co-selection effects for antibiotic resistance, little is known about whether and how they could promote antibiotic resistance spread via horizontal gene transfer across bacterial genera. This study, we report both CuO NPs and copper ions (Cu(2+)) could stimulate the conjugative transfer of multiple-drug resistance genes. When exposing bacteria to CuO NPs or Cu(2+) at environmental-relevant and sub-inhibitory concentrations (e.g., 1-100 μmol/L), conjugation frequencies of plasmid-encoded antibiotic resistance genes across genera (i.e., from Escherichia coli to Pseudomonas putida) were significantly enhanced (p < 0.05). The over-production of reactive oxygen species played a crucial role in promoting conjugative transfer. Genome-wide RNA and protein sequencing suggested expressional levels of genes and proteins related to oxidative stress, cell membrane permeability, and pilus generation were significantly up-regulated under CuO NPs and Cu(2+) exposure (p < 0.05). This study provides insights in the contributions of NPs and heavy metals on the spread of antibiotic resistance.201931158594
867760.9996Whole genome sequencing and comparative genomic analyses of Pseudomonas aeruginosa strain isolated from arable soil reveal novel insights into heavy metal resistance and codon biology. Elevated concentration of non-essential persistent heavy metals and metalloids in the soil is detrimental to essential soil microbes and plants, resulting in diminished diversity and biomass. Thus, isolation, screening, and whole genomic analysis of potent strains of bacteria from arable lands with inherent capabilities of heavy metal resistance and plant growth promotion hold the key for bio remedial applications. This study is an attempt to do the same. In this study, a potent strain of Pseudomonas aeruginosa was isolated from paddy fields, followed by metabolic profiling using FTIR, metal uptake analysis employing ICP-MS, whole genome sequencing and comparative codon usage analysis. ICP-MS study provided insights into a high degree of Cd uptake during the exponential phase of growth under cumulative metal stress to Cd, Zn and Co, which was further corroborated by the detection of cadA gene along with czcCBA operon in the genome upon performing whole-genome sequencing. This potent strain of Pseudomonas aeruginosa also harboured genes, such as copA, chrA, znuA, mgtE, corA, and others conferring resistance against different heavy metals, such as Cd, Zn, Co, Cu, Cr, etc. A comparative codon usage bias analysis at the genomic and genic level, whereby several heavy metal resistant genes were considered in the backdrop of two housekeeping genes among 40 Pseudomonas spp. indicated the presence of a relatively strong codon usage bias in the studied strain. With this work, an effort was made to explore heavy metal-resistant bacteria (isolated from arable soil) and whole genome sequence analysis to get insight into metal resistance for future bio remedial applications.202235763098
450970.9996Distribution of triclosan-resistant genes in major pathogenic microorganisms revealed by metagenome and genome-wide analysis. The substantial use of triclosan (TCS) has been aimed to kill pathogenic bacteria, but TCS resistance seems to be prevalent in microbial species and limited knowledge exists about TCS resistance determinants in a majority of pathogenic bacteria. We aimed to evaluate the distribution of TCS resistance determinants in major pathogenic bacteria (N = 231) and to assess the enrichment of potentially pathogenic genera in TCS contaminated environments. A TCS-resistant gene (TRG) database was constructed and experimentally validated to predict TCS resistance in major pathogenic bacteria. Genome-wide in silico analysis was performed to define the distribution of TCS-resistant determinants in major pathogens. Microbiome analysis of TCS contaminated soil samples was also performed to investigate the abundance of TCS-resistant pathogens. We experimentally confirmed that TCS resistance could be accurately predicted using genome-wide in silico analysis against TRG database. Predicted TCS resistant phenotypes were observed in all of the tested bacterial strains (N = 17), and heterologous expression of selected TCS resistant genes from those strains conferred expected levels of TCS resistance in an alternative host Escherichia coli. Moreover, genome-wide analysis revealed that potential TCS resistance determinants were abundant among the majority of human-associated pathogens (79%) and soil-borne plant pathogenic bacteria (98%). These included a variety of enoyl-acyl carrier protein reductase (ENRs) homologues, AcrB efflux pumps, and ENR substitutions. FabI ENR, which is the only known effective target for TCS, was either co-localized with other TCS resistance determinants or had TCS resistance-associated substitutions. Furthermore, microbiome analysis revealed that pathogenic genera with intrinsic TCS-resistant determinants exist in TCS contaminated environments. We conclude that TCS may not be as effective against the majority of bacterial pathogens as previously presumed. Further, the excessive use of this biocide in natural environments may selectively enrich for not only TCS-resistant bacterial pathogens, but possibly for additional resistance to multiple antibiotics.201829420585
386080.9996Mobility of antibiotic resistance and its co-occurrence with metal resistance in pathogens under oxidative stress. The bacterial communities are challenged with oxidative stress during their exposure to bactericidal antibiotics, metals, and different levels of dissolved oxygen (DO) encountered in diverse environmental habitats. The frequency of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) co-selection is increased by selective pressure posed by oxidative stress. Hence, study of resistance acquisition is important from an evolutionary perspective. To understand the dependence of oxidative stress on the dissemination of ARGs and MRGs through a pathogenic bacterial population, 12 metagenomes belonging to gut, water and soil habitats were evaluated. The metagenome-wide analysis showed the chicken gut to pose the most diverse pool of ARGs (30.4 ppm) and pathogenic bacteria (Simpson diversity = 0.98). The most common types of resistances found in all the environmental samples were efflux pumps (13.22 ppm) and genes conferring resistance to vancomycin (12.4 ppm), tetracycline (12.1 ppm), or beta-lactam (9.4 ppm) antibiotics. Additionally, limiting DO level in soil was observed to increase the abundance of excision nucleases (uvrA and uvrB), DNA polymerase (polA), catalases (katG), and other oxidative stress response genes (OSGs). This was further evident from major variations occurred in antibiotic efflux genes due to the effect of DO concentration on two human pathogens, namely Salmonella enterica and Shigella sonnei found in all the selected habitats. In conclusion, the microbial community, when challenged with oxidative stress caused by environmental variations in oxygen level, tends to accumulate higher amounts of ARGs with increased dissemination potential through triggering non-lethal mutagenesis. Furthermore, the genetic linkage or co-occurrence of ARGs and MRGs provides evidence for selecting ARGs under high concentrations of heavy metals.202134298350
472490.9996Transcriptomic analysis of sub-MIC Eugenol exposition on antibiotic resistance profile in Multidrug Resistant Enterococcus faecalis E9.8. The spread of multidrug-resistant (MDR) bacteria and their resistance genes along the food chain and the environment has become a global threat aggravated by incorrect disinfection strategies. This study analysed the effect of induction by sub-inhibitory concentrations of eugenol - a major ingredient in clove essential oil commonly used in disinfectant agents - on the phenotypic and genotypic response of MDR Enterococcus faecalis E9.8 strain, selected based on the phenotypic response of other enterococci. Eugenol treatment irreversibly reduced several antibiotics' minimum inhibitory concentration (MIC), confirmed by kinetic studies for kanamycin, erythromycin, and tetracycline. Furthermore, transcriptomic analysis indicated the reversion of antibiotic resistance through direct and indirect measures, such as down-regulation of genes coding for proteins involved in antibiotic resistance, toxin resistance and virulence factors. Regarding antibiotic resistance genes (ARGs), ten differentially expressed genes (five down-regulated and five up-regulated genes) were related to the main transporter families, which present key targets in antibiotic resistance reversion. Our study thus highlights the importance of considering indirectly related genes as targets for antibiotic resistance reversion besides ARGs sensu stricto. These results allow us to propose using eugenol as an antibiotic resistance reversing agent to be included in disinfectant solutions as an excellent alternative to limit the spread of MDR bacteria and their ARGs in the food chain and the environment.202539827501
8951100.9996Response mechanisms of resistance in L-form bacteria to different target antibiotics: Implications from oxidative stress to metabolism. Due to the specific action on bacterial cell wall, β-lactam antibiotics have gained widespread usage as they exhibit a high degree of specificity in targeting bacteria, but causing minimal toxicity to host cells. Under antibiotic pressure, bacteria may opt to shed their cell walls and transform into L-form state as a means to evade the antibiotic effects. In this study, we explored and identified diverse optimal conditions for both Gram-negative bacteria (E. coli DH5α (CTX)) and Gram-positive bacteria (B. subtilis ATCC6633), which were induced to L-form bacteria using lysozyme (0.5 ppm) and meropenem (64 ppm). Notably, when bacteria transformed into L-form state, both bacterial strains showed varying degrees of increased resistance to antibiotics polymyxin E, meropenem, rifampicin, and tetracycline. E. coli DH5α (CTX) exhibited the most significant enhancement in resistance to tetracycline, with a 128-fold increase, while B. subtilis ATCC6633 showed a 32-fold increase in resistance to tetracycline and polymyxin E. Furthermore, L-form bacteria maintained their normal metabolic activity, combined with enhanced oxidative stress, served as an adaptive strategy promoting the sustained survival of L-form bacteria. This study provided a theoretical basis for comprehending antibiotic resistance mechanisms, developing innovative treatment strategies, and confronting global antibiotic resistance challenges.202438735077
3852110.9996Phenotype profiles and adaptive preference of Acinetobacter johnsonii isolated from Ba River with different environmental backgrounds. Acinetobacter johnsonii is a potentially opportunistic pathogen widely distributed in nosocomial and natural environments, but little attention has been paid to this bacillus. Here A. johnsonii strains from Ba River with different pollution levels were isolated. In this study, we found that the increasing anthropogenic contaminants accounted for the emergence of multidrug-resistant (MDR) A. johnsonii strains. Correlation analysis results showed that the resistance phenotype of strains could be generated by co-selection of heavy metals or non-corresponding antibiotics. The whole genome sequence analysis showed that the relative heavy pollution of water selects strains containing more survival-relevant genes. We found that only some genes like bla(OXA-24) were responsible for its corresponding resistance profile. Additionally, the tolerance profiles toward heavy metals also attribute to the expression of efflux pumps rather than corresponding resistance genes. In summary, our finding revealed that the resistance profiles of A. johnsonii could be generated by cross or co-selection of anthropogenic contaminants and mediated by efflux pumps instead of corresponding resistance determinants. Our study also has deep-sight into the adaptive preference of bacteria in natural environments, and contributes to surveillance studies and MDR- A. johnsonii monitoring worldwide.202133639142
3859120.9996Co-selection of antibiotic resistance via copper shock loading on bacteria from a drinking water bio-filter. Heavy metal contamination of source water frequently occurred in developing countries as a result of accidents. To address the problems, most of the previous studies have focused on engineering countermeasures. In this study, we investigated the effects of heavy metals, particularly copper, on the development of antibiotic resistance by establishing a copper shock loading test. Results revealed that co-selection occurred rapidly within 6 h. Copper, at the levels of 10 and 100 mg/L, significantly increased bacterial resistance to the antibiotics tested, including rifampin, erythromycin, kanamycin, and a few others. A total of 117 antimicrobial-resistance genes were detected from 12 types of genes, and the relative abundance of most genes (particularly mobile genetic elements intⅠand transposons) was markedly enriched by at least one fold. Furthermore, the copper shock loading altered the bacterial community. Numerous heavy metal and antibiotic resistant strains were screened out and enriched. These strains are expected to enhance the overall level of resistance. More noticeably, the majority of the co-selected antibiotic resistance could sustain for at least 20 h in the absence of copper and antimicrobial drugs. Resistance to vancomycin, erythromycin and lincomycin even could remain for 7 days. The prominent selection pressure by the copper shock loading implies that a real accident most likely poses similar impacts on the water environment. An accidental release of heavy metals would not only cause harm to the ecological environment, but also contribute to the development of bacterial antibiotic resistance. Broader concerns should be raised about the biological risks caused by sudden releases of pollutants by accidents.201829059628
3710130.9996Tolerance to various toxicants by marine bacteria highly resistant to mercury. Bacteria highly resistant to mercury isolated from seawater and sediment samples were tested for growth in the presence of different heavy metals, pesticides, phenol, formaldehyde, formic acid, and trichloroethane to investigate their potential for growth in the presence of a variety of toxic xenobiotics. We hypothesized that bacteria resistant to high concentrations of mercury would have potential capacities to tolerate or possibly degrade a variety of toxic materials and thus would be important in environmental pollution bioremediation. The mercury-resistant bacteria were found to belong to Pseudomonas, Proteus, Xanthomonas, Alteromonas, Aeromonas, and Enterobacteriaceae. All these environmental bacterial strains tolerant to mercury used in this study were capable of growth at a far higher concentration (50 ppm) of mercury than previously reported. Likewise, their ability to grow in the presence of toxic xenobiotics, either singly or in combination, was superior to that of bacteria incapable of growth in media containing 5 ppm mercury. Plasmid-curing assays done in this study ascertained that resistance to mercury antibiotics, and toxic xenobiotics is mediated by chromosomally borne genes and/or transposable elements rather than by plasmids.200312876655
6785140.9996Combined impact of antibiotics and Cr(VI) on antibiotic resistance, ARGs, and growth of Bacillussp. SH-1: A functionl analysis from gene to protease. The simultaneous selection of antibiotic resistance genes (ARGs) induced by heavy metals and antibiotics has emerged as a growing environmental problem. This study investigated the combined effects of chromium (Cr(VI)) and antibiotics on the ARGs of Bacillus cereus SH-1. As Cr(VI) concentration increased, it triggered reactive oxygen species oxidative stress in SH-1, increased antioxidant enzyme activity, enhanced plasmid conjugative transfer, and reduced the efficiency of Cr(VI) removal by SH-1. Antibiotic resistance varied with increasing tetracycline and amoxicillin minimum inhibitory concentrations (MICs), whereas azithromycin and chloramphenicol MICs decreased with Cr(VI) induction. The overexpression of eight genes of the HAE-1 family of efflux pumps was detected using metagenomics and proteomics. Co-contamination with Cr(VI) and antibiotics has led to the emergence and spread of antibiotic-resistant bacteria. Therefore, resistance gene contamination resulting from Cr(VI)-polluted environments cannot be overlooked.202439384050
3904150.9996Association of antibiotics and heavy metal arsenic to horizontal gene transfer from multidrug-resistant clinical strains to antibiotic-sensitive environmental strains. The emergence of multidrug-resistant bacteria is currently posing a significant threat to global public health. By testing for resistance to different antibiotic classes, we discovered that the majority of clinical bacteria are multidrug-resistant. These clinical multidrug-resistant species have antibiotic resistance genes on their plasmids that can be horizontally transferred to various antibiotic susceptible environmental bacterial species, resulting in antibiotic-resistant transconjugates. Furthermore, we discovered that the presence of an optimal concentration of antibiotics or heavy metal (arsenic) facilitates horizontal gene transfer through the formation of transconjugants. Notably, the addition of a conjugation inhibitor (2-hexadecynoic acid, a synthetic fatty acid) completely blocked the formation of antibiotic or arsenic-induced transconjugants. We discovered a high level of arsenic in water from the Shukratal region, Uttarakhand, India, which corresponded to a high serum level of arsenic in clinically infected individuals from the Shukratal region compared to other locations in Uttarakhand. Importantly, bacterial strains isolated from infected people who drink water from the Shukratal region with high arsenic levels were found to be more antibiotic-resistant than strains isolated from other sites. We discovered that bacterial strains isolated from individuals with high serum arsenic levels are significantly more resistant to antibiotics than individuals with low serum arsenic levels within the Shurkratal. This research sheds light on imminent threats to global health in which improper clinical, industrial, and other waste disposal, increased antibiotic concentrations in the environment, and increased human interference can easily transform commensal and pathogenic bacteria found in environmental niches into life-threatening multidrug-resistant superbugs.202336327832
3709160.9996Potential of tellurite resistance in heterotrophic bacteria from mining environments. Untreated mining wastes and improper disposal of high-tech devices generate an environmental increase of bioavailable metalloids, exerting stress on autochthonous microbial populations. Tellurium is a metalloid, an element with raising economic importance; nevertheless, its interaction with living organisms is not yet fully understood. Here we characterized aerobic heterotrophic bacteria, isolated from high metal-content mining residues, able to resist/reduce tellurite into tellurium structures and to determine the presence of confirmed tellurite resistance genetic determinants in resistant strains. We identified over 50 tellurite-resistant strains, among 144 isolates, eight strains reduced tellurite to tellurium at different rates, with the concomitant production of tellurium deposits. Most tellurite resistance genes were found in strains from Bacillales, with the prevalence of genes of the ter operon. This work demonstrated that bacterial isolates, from environments with a persistent selective pressure, are potential candidates for uncovering strategies for tellurite resistance and/or production of valuable Te-containing materials.202235784792
3853170.9996Co-selection of antibiotic-resistant bacteria in a paddy soil exposed to As(III) contamination with an emphasis on potential pathogens. The increased acquisition of antibiotic resistance by pathogens is a global health concern. The environmental selection of antibiotic resistance can be caused by either antibiotic residues or co-selecting agents such as toxic metal(loid)s. This study explored the potential role of As(III) as a co-selecting driver in the spread of antibiotic resistance in paddy soils. By applying high-throughput sequencing, we found that the diversity and composition of soil microbial communities was significantly altered by As(III) exposure, resulting in an increased proportion of potential pathogens (9.9%) compared to the control soil (0.1%). Meanwhile, a total of 46 As(III)-resistant isolates were obtained from As(III)-exposure soil, among which potential pathogens accounted for 54.3%. These As(III)-resistant bacteria showed a high incidence of resistance to sulfanilamide (100%) and streptomycin (88-93%). The association between antibiotic and As(III) resistances was further investigated in a potentially pathogenic isolate by whole-genome sequencing and a transcription assay. The results showed that As(III) and antibiotic resistance genes might co-occur in a mobile genomic island and be co-regulated by As(III), implying that antibiotic resistance could be co-selected by As(III) via co-resistance and co-regulation mechanisms. Overall, these results suggest that As(III) exposure provides a strong selective pressure for the expansion of soil bacterial resistome.202032302839
3793180.9996Physicochemical Factors That Favor Conjugation of an Antibiotic Resistant Plasmid in Non-growing Bacterial Cultures in the Absence and Presence of Antibiotics. Horizontal gene transfer (HGT) of antibiotic resistance genes has received increased scrutiny from the scientific community in recent years owing to the public health threat associated with antibiotic resistant bacteria. Most studies have examined HGT in growing cultures. We examined conjugation in growing and non-growing cultures of E. coli using a conjugative multi antibiotic and metal resistant plasmid to determine physiochemical parameters that favor horizontal gene transfer. The conjugation frequency in growing and non-growing cultures was generally greater under shaken than non-shaken conditions, presumably due to increased frequency of cell collisions. Non-growing cultures in 9.1 mM NaCl had a similar conjugation frequency to that of growing cultures in Luria-Bertaini broth, whereas those in 1 mM or 90.1 mM NaCl were much lower. This salinity effect on conjugation was attributed to differences in cell-cell interactions and conformational changes in cell surface macromolecules. In the presence of antibiotics, the conjugation frequencies of growing cultures did not increase, but in non-growing cultures of 9.1 mM NaCl supplemented with Cefotaxime the conjugation frequency was as much as nine times greater than that of growing cultures. The mechanism responsible for the increased conjugation in non-growing bacteria was attributed to the likely lack of penicillin-binding protein 3 (the target of Cefotaxime), in non-growing cells that enabled Cefotaxime to interact with the plasmid and induce conjugation. Our results suggests that more attention may be owed to HGT in non-growing bacteria as most bacteria in the environment are likely not growing and the proposed mechanism for increased conjugation may not be unique to the bacteria/plasmid system we studied.201830254617
6108190.9996Genes involved in arsenic transformation and resistance associated with different levels of arsenic-contaminated soils. BACKGROUND: Arsenic is known as a toxic metalloid, which primarily exists in inorganic form [As(III) and As(V)] and can be transformed by microbial redox processes in the natural environment. As(III) is much more toxic and mobile than As(V), hence microbial arsenic redox transformation has a major impact on arsenic toxicity and mobility which can greatly influence the human health. Our main purpose was to investigate the distribution and diversity of microbial arsenite-resistant species in three different arsenic-contaminated soils, and further study the As(III) resistance levels and related functional genes of these species. RESULTS: A total of 58 arsenite-resistant bacteria were identified from soils with three different arsenic-contaminated levels. Highly arsenite-resistant bacteria (MIC > 20 mM) were only isolated from the highly arsenic-contaminated site and belonged to Acinetobacter, Agrobacterium, Arthrobacter, Comamonas, Rhodococcus, Stenotrophomonas and Pseudomonas. Five arsenite-oxidizing bacteria that belonged to Achromobacter, Agrobacterium and Pseudomonas were identified and displayed a higher average arsenite resistance level than the non-arsenite oxidizers. 5 aoxB genes encoding arsenite oxidase and 51 arsenite transporter genes [18 arsB, 12 ACR3(1) and 21 ACR3(2)] were successfully amplified from these strains using PCR with degenerate primers. The aoxB genes were specific for the arsenite-oxidizing bacteria. Strains containing both an arsenite oxidase gene (aoxB) and an arsenite transporter gene (ACR3 or arsB) displayed a higher average arsenite resistance level than those possessing an arsenite transporter gene only. Horizontal transfer of ACR3(2) and arsB appeared to have occurred in strains that were primarily isolated from the highly arsenic-contaminated soil. CONCLUSION: Soils with long-term arsenic contamination may result in the evolution of highly diverse arsenite-resistant bacteria and such diversity was probably caused in part by horizontal gene transfer events. Bacteria capable of both arsenite oxidation and arsenite efflux mechanisms had an elevated arsenite resistance level.200919128515