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10900.9574Identification of two putative ATP-cassette genes in Encephalitozoon intestinalis. Currently existing chemotherapeutic compounds are limited and few are effective for treating microsporidiosis. It is possible that resistance of Encephalitozoon to some drugs occurs by efflux mechanisms similar to those previously described for mammalian tumour cells, bacteria or protozoal parasites such as Plasmodium, Leishmania and Entamoeba histolytica. The data in the present study suggest that Encephalitozoon intestinalis contains at least one multidrug resistance gene. We report here two complete sequences EiABC1 and EiABC2, encoding different ATP-binding cassette genes from E. intestinalis, including a P-gp.200111730796
23110.9495Lincosamides, Streptogramins, Phenicols, and Pleuromutilins: Mode of Action and Mechanisms of Resistance. Lincosamides, streptogramins, phenicols, and pleuromutilins (LSPPs) represent four structurally different classes of antimicrobial agents that inhibit bacterial protein synthesis by binding to particular sites on the 50S ribosomal subunit of the ribosomes. Members of all four classes are used for different purposes in human and veterinary medicine in various countries worldwide. Bacteria have developed ways and means to escape the inhibitory effects of LSPP antimicrobial agents by enzymatic inactivation, active export, or modification of the target sites of the agents. This review provides a comprehensive overview of the mode of action of LSPP antimicrobial agents as well as of the mutations and resistance genes known to confer resistance to these agents in various bacteria of human and animal origin.201627549310
815720.9495Autologous DNA mobilization and multiplication expedite natural products discovery from bacteria. The transmission of antibiotic-resistance genes, comprising mobilization and relocation events, orchestrates the dissemination of antimicrobial resistance. Inspired by this evolutionarily successful paradigm, we developed ACTIMOT, a CRISPR-Cas9-based approach to unlock the vast chemical diversity concealed within bacterial genomes. ACTIMOT enables the efficient mobilization and relocation of large DNA fragments from the chromosome to replicative plasmids within the same bacterial cell. ACTIMOT circumvents the limitations of traditional molecular cloning methods involving handling and replicating large pieces of genomic DNA. Using ACTIMOT, we mobilized and activated four cryptic biosynthetic gene clusters from Streptomyces, leading to the discovery of 39 compounds across four distinct classes. This work highlights the potential of ACTIMOT for accelerating the exploration of biosynthetic pathways and the discovery of natural products.202439666857
999030.9492Axe-Txe, a broad-spectrum proteic toxin-antitoxin system specified by a multidrug-resistant, clinical isolate of Enterococcus faecium. Enterococcal species of bacteria are now acknowledged as leading causes of bacteraemia and other serious nosocomial infections. However, surprisingly little is known about the molecular mechanisms that promote the segregational stability of antibiotic resistance and other plasmids in these bacteria. Plasmid pRUM (24 873 bp) is a multidrug resistance plasmid identified in a clinical isolate of Enterococcus faecium. A novel proteic-based toxin-antitoxin cassette identified on pRUM was demonstrated to be a functional segregational stability module in both its native host and evolutionarily diverse bacterial species. Induced expression of the toxin protein (Txe) of this system resulted in growth inhibition in Escherichia coli. The toxic effect of Txe was alleviated by co-expression of the antitoxin protein, Axe. Homologues of the axe and txe genes are present in the genomes of a diversity of Eubacteria. These homologues (yefM-yoeB) present in the E. coli chromosome function as a toxin-antitoxin mechanism, although the Axe and YefM antitoxin components demonstrate specificity for their cognate toxin proteins in vivo. Axe-Txe is one of the first functional proteic toxin-antitoxin systems to be accurately described for Gram-positive bacteria.200312603745
911740.9490Antimicrobial Resistance and the Alternative Resources with Special Emphasis on Plant-Based Antimicrobials-A Review. Indiscriminate and irrational use of antibiotics has created an unprecedented challenge for human civilization due to microbe's development of antimicrobial resistance. It is difficult to treat bacterial infection due to bacteria's ability to develop resistance against antimicrobial agents. Antimicrobial agents are categorized according to their mechanism of action, i.e., interference with cell wall synthesis, DNA and RNA synthesis, lysis of the bacterial membrane, inhibition of protein synthesis, inhibition of metabolic pathways, etc. Bacteria may become resistant by antibiotic inactivation, target modification, efflux pump and plasmidic efflux. Currently, the clinically available treatment is not effective against the antibiotic resistance developed by some bacterial species. However, plant-based antimicrobials have immense potential to combat bacterial, fungal, protozoal and viral diseases without any known side effects. Such plant metabolites include quinines, alkaloids, lectins, polypeptides, flavones, flavonoids, flavonols, coumarin, terpenoids, essential oils and tannins. The present review focuses on antibiotic resistance, the resistance mechanism in bacteria against antibiotics and the role of plant-active secondary metabolites against microorganisms, which might be useful as an alternative and effective strategy to break the resistance among microbes.201728394295
818550.9485RNA-cleaving DNAzymes as a diagnostic and therapeutic agent against antimicrobial resistant bacteria. The development of nucleic-acid-based antimicrobials such as RNA-cleaving DNAzyme (RCD), a short catalytically active nucleic acid, is a promising alternative to the current antibiotics. The current rapid spread of antimicrobial resistance (AMR) in bacteria renders some antibiotics useless against bacterial infection, thus creating the need for alternative antimicrobials such as DNAzymes. This review summarizes recent advances in the use of RCD as a diagnostic and therapeutic agent against AMR. Firstly, the recent diagnostic application of RCD for the detection of bacterial cells and the associated resistant gene(s) is discussed. The next section summarises the therapeutic application of RCD in AMR bacterial infections which includes direct targeting of the resistant genes and indirect targeting of AMR-associated genes. Finally, this review extends the discussion to challenges of utilizing RCD in real-life applications, and the potential of combining both diagnostic and therapeutic applications of RCD into a single agent as a theranostic agent.202234505182
11060.9483Resistance to the macrolide antibiotic tylosin is conferred by single methylations at 23S rRNA nucleotides G748 and A2058 acting in synergy. The macrolide antibiotic tylosin has been used extensively in veterinary medicine and exerts potent antimicrobial activity against Gram-positive bacteria. Tylosin-synthesizing strains of the Gram-positive bacterium Streptomyces fradiae protect themselves from their own product by differential expression of four resistance determinants, tlrA, tlrB, tlrC, and tlrD. The tlrB and tlrD genes encode methyltransferases that add single methyl groups at 23S rRNA nucleotides G748 and A2058, respectively. Here we show that methylation by neither TlrB nor TlrD is sufficient on its own to give tylosin resistance, and resistance is conferred by the G748 and A2058 methylations acting together in synergy. This synergistic mechanism of resistance is specific for the macrolides tylosin and mycinamycin that possess sugars extending from the 5- and 14-positions of the macrolactone ring and is not observed for macrolides, such as carbomycin, spiramycin, and erythromycin, that have different constellations of sugars. The manner in which the G748 and A2058 methylations coincide with the glycosylation patterns of tylosin and mycinamycin reflects unambiguously how these macrolides fit into their binding site within the bacterial 50S ribosomal subunit.200212417742
815870.9481Nanobioconjugates: Weapons against Antibacterial Resistance. The increase in drug resistance in pathogenic bacteria is emerging as a global threat as we swiftly edge toward the postantibiotic era. Nanobioconjugates have gained tremendous attention to treat multidrug-resistant (MDR) bacteria and biofilms due to their tunable physicochemical properties, drug targeting ability, enhanced uptake, and alternate mechanisms of drug action. In this review, we highlight the recent advances made in the use of nanobioconjugates to combat antibacterial resistance and provide crucial insights for designing nanomaterials that can serve as antibacterial agents for nanotherapeutics, nanocargos for targeted antibiotic delivery, or both. Also discussed are different strategies for treating robust biofilms formed by bacteria.202035019602
56280.9480Macrolones target bacterial ribosomes and DNA gyrase and can evade resistance mechanisms. Growing resistance toward ribosome-targeting macrolide antibiotics has limited their clinical utility and urged the search for superior compounds. Macrolones are synthetic macrolide derivatives with a quinolone side chain, structurally similar to DNA topoisomerase-targeting fluoroquinolones. While macrolones show enhanced activity, their modes of action have remained unknown. Here, we present the first structures of ribosome-bound macrolones, showing that the macrolide part occupies the macrolide-binding site in the ribosomal exit tunnel, whereas the quinolone moiety establishes new interactions with the tunnel. Macrolones efficiently inhibit both the ribosome and DNA topoisomerase in vitro. However, in the cell, they target either the ribosome or DNA gyrase or concurrently both of them. In contrast to macrolide or fluoroquinolone antibiotics alone, dual-targeting macrolones are less prone to select resistant bacteria carrying target-site mutations or to activate inducible macrolide resistance genes. Furthermore, because some macrolones engage Erm-modified ribosomes, they retain activity even against strains with constitutive erm resistance genes.202439039256
22890.9475Resistance to nonribosomal peptide antibiotics mediated by D-stereospecific peptidases. Nonribosomal peptide antibiotics, including polymyxin, vancomycin, and teixobactin, most of which contain D-amino acids, are highly effective against multidrug-resistant bacteria. However, overusing antibiotics while ignoring the risk of resistance arising has inexorably led to widespread emergence of resistant bacteria. Therefore, elucidation of the emerging mechanisms of resistance to nonribosomal peptide antibiotics is critical to their implementation. Here we describe a networking-associated genome-mining platform for linking biosynthetic building blocks to resistance components associated with biosynthetic gene clusters. By applying this approach to 5,585 complete bacterial genomes spanning the entire domain of bacteria, with subsequent chemical and enzymatic analyses, we demonstrate a mechanism of resistance toward nonribosomal peptide antibiotics that is based on hydrolytic cleavage by D-stereospecific peptidases. Our finding reveals both the widespread distribution and broad-spectrum resistance potential of D-stereospecific peptidases, providing a potential early indicator of antibiotic resistance to nonribosomal peptide antibiotics.201829483640
611100.9473The Staphylococcus aureus FASII bypass escape route from FASII inhibitors. Antimicrobials targeting the fatty acid synthesis (FASII) pathway are being developed as alternative treatments for bacterial infections. Emergence of resistance to FASII inhibitors was mainly considered as a consequence of mutations in the FASII target genes. However, an alternative and efficient anti-FASII resistance strategy, called here FASII bypass, was uncovered. Bacteria that bypass FASII incorporate exogenous fatty acids in membrane lipids, and thus dispense with the need for FASII. This strategy is used by numerous Gram-positive low GC % bacteria, including streptococci, enterococci, and staphylococci. Some bacteria repress FASII genes once fatty acids are available, and "constitutively" shift to FASII bypass. Others, such as the major pathogen Staphylococcus aureus, can undergo high frequency mutations that favor FASII bypass. This capacity is particularly relevant during infection, as the host supplies the fatty acids needed for bacteria to bypass FASII and thus become resistant to FASII inhibitors. Screenings for anti-FASII resistance in the presence of exogenous fatty acids confirmed that FASII bypass confers anti-FASII resistance among clinical and veterinary isolates. Polymorphisms in S. aureus FASII initiation enzymes favor FASII bypass, possibly by increasing availability of acyl-carrier protein, a required intermediate. Here we review FASII bypass and consequences in light of proposed uses of anti-FASII to treat infections, with a focus on FASII bypass in S. aureus.201728728970
9178110.9472Targeting non-multiplying organisms as a way to develop novel antimicrobials. Increasing resistance and decreasing numbers of antibiotics reaching the market point to a growing need for novel antibacterial drugs. Most antibiotics are very inefficient at killing non-multiplying bacteria, which live side by side with multiplying ones of the same strain in a clinical infection. Although non-multiplying bacteria do not usually cause disease, they can revert to the multiplying state that leads to overt disease, at which time resistance can emerge. Here we discuss the concept of developing antibacterial drugs by targeting non-multiplying organisms. We define non-multiplying bacteria, discuss the efficacy of existing antibiotics, and assess whether targeting these bacteria might lead to new antibiotics that will decrease the rate of emergence of resistance. Lastly, we review the potential of new molecular targets and live non-multiplying bacteria as possible routes for the development of novel antimicrobial drugs.200818262665
9177120.9470Multitarget Approaches against Multiresistant Superbugs. Despite efforts to develop new antibiotics, antibacterial resistance still develops too fast for drug discovery to keep pace. Often, resistance against a new drug develops even before it reaches the market. This continued resistance crisis has demonstrated that resistance to antibiotics with single protein targets develops too rapidly to be sustainable. Most successful long-established antibiotics target more than one molecule or possess targets, which are encoded by multiple genes. This realization has motivated a change in antibiotic development toward drug candidates with multiple targets. Some mechanisms of action presuppose multiple targets or at least multiple effects, such as targeting the cytoplasmic membrane or the carrier molecule bactoprenol phosphate and are therefore particularly promising. Moreover, combination therapy approaches are being developed to break antibiotic resistance or to sensitize bacteria to antibiotic action. In this Review, we provide an overview of antibacterial multitarget approaches and the mechanisms behind them.202032156116
9122130.9470The role of bacterial transport systems in the removal of host antimicrobial peptides in Gram-negative bacteria. Antibiotic resistance is a global issue that threatens our progress in healthcare and life expectancy. In recent years, antimicrobial peptides (AMPs) have been considered as promising alternatives to the classic antibiotics. AMPs are potentially superior due to their lower rate of resistance development, since they primarily target the bacterial membrane ('Achilles' heel' of the bacteria). However, bacteria have developed mechanisms of AMP resistance, including the removal of AMPs to the extracellular space by efflux pumps such as the MtrCDE or AcrAB-TolC systems, and the internalization of AMPs to the cytoplasm by the Sap transporter, followed by proteolytic digestion. In this review, we focus on AMP transport as a resistance mechanism compiling all the experimental evidence for the involvement of efflux in AMP resistance in Gram-negative bacteria and combine this information with the analysis of the structures of the efflux systems involved. Finally, we expose some open questions with the aim of arousing the interest of the scientific community towards the AMPs-efflux pumps interactions. All the collected information broadens our understanding of AMP removal by efflux pumps and gives some clues to assist the rational design of AMP-derivatives as inhibitors of the efflux pumps.202235749576
9762140.9468AcrAB-TolC, a major efflux pump in Gram negative bacteria: toward understanding its operation mechanism. Antibiotic resistance (AR) is a silent pandemic that kills millions worldwide. Although the development of new therapeutic agents against antibiotic resistance is in urgent demand, this has presented a great challenge, especially for Gram-negative bacteria that have inherent drug-resistance mediated by impermeable outer membranes and multidrug efflux pumps that actively extrude various drugs from the bacteria. For the last two decades, multidrug efflux pumps, including AcrAB-TolC, the most clinically important efflux pump in Gram-negative bacteria, have drawn great attention as strategic targets for re-sensitizing bacteria to the existing antibiotics. This article aims to provide a concise overview of the AcrAB-TolC operational mechanism, reviewing its architecture and substrate specificity, as well as the recent development of AcrAB-TolC inhibitors. [BMB Reports 2023; 56(6): 326-334].202337254571
111150.9468The tylosin resistance gene tlrB of Streptomyces fradiae encodes a methyltransferase that targets G748 in 23S rRNA. tlrB is one of four resistance genes encoded in the operon for biosynthesis of the macrolide tylosin in antibiotic-producing strains of Streptomyces fradiae. Introduction of tlrB into Streptomyces lividans similarly confers tylosin resistance. Biochemical analysis of the rRNA from the two Streptomyces species indicates that in vivo TlrB modifies nucleotide G748 within helix 35 of 23S rRNA. Purified recombinant TlrB retains its activity and specificity in vitro and modifies G748 in 23S rRNA as well as in a 74 nucleotide RNA containing helix 35 and surrounding structures. Modification is dependent on the presence of the methyl group donor, S-adenosyl methionine. Analysis of the 74-mer RNA substrate by biochemical and mass spectrometric methods shows that TlrB adds a single methyl group to the base of G748. Homologues of TlrB in other bacteria have been revealed through database searches, indicating that TlrB is the first member to be described in a new subclass of rRNA methyltransferases that are implicated in macrolide drug resistance.200010972803
9123160.9467Antibiotic resistance of bacteria in biofilms. Bacteria that adhere to implanted medical devices or damaged tissue can encase themselves in a hydrated matrix of polysaccharide and protein, and form a slimy layer known as a biofilm. Antibiotic resistance of bacteria in the biofilm mode of growth contributes to the chronicity of infections such as those associated with implanted medical devices. The mechanisms of resistance in biofilms are different from the now familiar plasmids, transposons, and mutations that confer innate resistance to individual bacterial cells. In biofilms, resistance seems to depend on multicellular strategies. We summarise the features of biofilm infections, review emerging mechanisms of resistance, and discuss potential therapies.200111463434
5132170.9467The genome of Symbiodiniaceae-associated Stutzerimonas frequens CAM01 reveals a broad spectrum of antibiotic resistance genes indicating anthropogenic drift in the Palk Bay coral reef of south-eastern India. An increase in antibiotic pollution in reef areas will lead to the emergence of antibiotic-resistant bacteria, leading to ecological disturbances in the sensitive coral holobiont. This study provides insights into the genome of antibiotics-resistant Stutzerimonas frequens CAM01, isolated from Favites-associated Symbiodiniaceae of a near-shore polluted reef of Palk Bay, India. The draft genome contains 4.67 Mbp in size with 52 contigs. Further genome analysis revealed the presence of four antibiotic-resistant genes, namely, adeF, rsmA, APH (3")-Ib, and APH (6)-Id that provide resistance by encoding resistance-nodulation-cell division (RND) antibiotic efflux pump and aminoglycoside phosphotransferase. The isolate showed resistance against 73% of the antibiotics tested, concurrent with the predicted AMR genes. Four secondary metabolites, namely Aryl polyene, NRPS-independent-siderophore, terpenes, and ectoine were detected in the isolate, which may play a role in virulence and pathogenicity adaptation in microbes. This study provides key insights into the genome of Stutzerimonas frequens CAM01 and highlights the emergence of antibiotic-resistant bacteria in coral reef ecosystems.202337626254
9156180.9467Resistance to quorum-quenching compounds. Bacteria have the remarkable ability to communicate as a group in what has become known as quorum sensing (QS), and this trait has been associated with important bacterial phenotypes, such as virulence and biofilm formation. Bacteria also have an incredible ability to evolve resistance to all known antimicrobials. Hence, although inhibition of QS has been hailed as a means to reduce virulence in a manner that is impervious to bacterial resistance mechanisms, this approach is unlikely to be a panacea. Here we review the evidence that bacteria can evolve resistance to quorum-quenching compounds.201324014536
9793190.9467Recent Review on Subclass B1 Metallo-β-lactamases Inhibitors: Sword for Antimicrobial Resistance. An emerging crisis of antibiotic resistance for microbial pathogens is alarming all the nations, posing a global threat to human health. The production of the metalloβ-lactamase enzyme is the most powerful strategy of bacteria to produce resistance. An efficient way to combat this global health threat is the development of broad/non-specific type of metalloβ-lactamase inhibitors, which can inhibit the different isoforms of the enzyme. Till date, there are no clinically active drugs against metallo- β-lactamase. The lack of efficient drug molecules against MBLs carrying bacteria requires continuous research efforts to overcome the problem of multidrug-resistance bacteria. The present review will discuss the clinically potent molecules against different variants of B1 metalloβ-lactamase.201930556502