Comparative Drug Resistance Reversal Potential of Natural Glycosides: Potential of Synergy Niaziridin & Niazirin. - Related Documents




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636701.0000Comparative Drug Resistance Reversal Potential of Natural Glycosides: Potential of Synergy Niaziridin & Niazirin. BACKGROUND: Due to the limited availability of antibiotics, Gram-negative bacteria (GNB) acquire different levels of drug resistance. It raised an urgent need to identify such agents, which can reverse the phenomenon of drug resistance. OBJECTIVE: To understand the mechanism of drug resistance reversal of glycosides; niaziridin and niazirin isolated from the pods of Moringa oleifera and ouabain (control) against the clinical isolates of multidrug-resistant Escherichia coli. METHODS: The MICs were determined following the CLSI guidelines for broth micro-dilution. In-vitro combination studies were performed by broth checkerboard method followed by Time-Kill studies, the efflux pump inhibition assay, ATPase inhibitory activity, mutation prevention concentration and in-silico studies. RESULTS: The results showed that both glycosides did not possess antibacterial activity of their own, but in combination, they reduced the MIC of tetracycline up to 16 folds. Both were found to inhibit efflux pumps, but niaziridin was the best. In real time expression pattern analysis, niaziridin was also found responsible for the down expression of the two important efflux pump acrB & yojI genes alone as well as in combination. Niaziridin was also able to over express the porin forming genes (ompA & ompX). These glycosides decreased the mutation prevention concentration of tetracycline. CONCLUSION: This is the first ever report on glycosides, niazirin and niaziridin acting as drug resistance reversal agent through efflux pump inhibition and modulation of expression pattern drug resistant genes. This study may be helpful in preparing an effective antibacterial combination against the drug-resistant GNB from a widely growing Moringa oleifera.201930977451
618510.9989Effects of efflux transporter genes on susceptibility of Escherichia coli to tigecycline (GAR-936). The activity of tigecycline, 9-(t-butylglycylamido)-minocycline, against Escherichia coli KAM3 (acrB) strains harboring plasmids encoding various tetracycline-specific efflux transporter genes, tet(B), tet(C), and tet(K), and multidrug transporter genes, acrAB, acrEF, and bcr, was examined. Tigecycline showed potent activity against all three Tet-expressing, tetracycline-resistant strains, with the MICs for the strains being equal to that for the host strain. In the Tet(B)-containing vesicle study, tigecycline did not significantly inhibit tetracycline efflux-coupled proton translocation and at 10 microM did not cause proton translocation. This suggests that tigecycline is not recognized by the Tet efflux transporter at a low concentration; therefore, it exhibits significant antibacterial activity. These properties can explain its potent activity against bacteria with a Tet efflux resistance determinant. Tigecycline induced the Tet(B) protein approximately four times more efficiently than tetracycline, as determined by Western blotting, indicating that it is at least recognized by a TetR repressor. The MICs for multidrug efflux proteins AcrAB and AcrEF were increased fourfold. Tigecycline inhibited active ethidium bromide efflux from intact E. coli cells overproducing AcrAB. Therefore, tigecycline is a possible substrate of AcrAB and its close homolog, AcrEF, which are resistance-modulation-division-type multicomponent efflux transporters.200415155219
575520.9988Effects of Efflux Pump Inhibitors on Colistin Resistance in Multidrug-Resistant Gram-Negative Bacteria. We tested the effects of various putative efflux pump inhibitors on colistin resistance in multidrug-resistant Gram-negative bacteria. Addition of 10 mg/liter cyanide 3-chlorophenylhydrazone (CCCP) to the test medium could significantly decrease the MICs of colistin-resistant strains. Time-kill assays showed CCCP could reverse colistin resistance and inhibit the regrowth of the resistant subpopulation, especially in Acinetobacter baumannii and Stenotrophomonas maltophilia These results suggest colistin resistance in Gram-negative bacteria can be suppressed and reversed by CCCP.201626953203
905330.9988Nordihydroguaiaretic acid reverses the antibacterial activity of colistin against MCR-1-positive bacteria in vivo/in vitro by inhibiting MCR-1 activity and injuring the bacterial cell membrane. BACKGROUND: Colistin (polymyxin E) is an effective antibiotic for the treatment of most multidrug-resistant Gram-negative bacteria. However, some bacteria, including bacterial spp. belonging to the Enterobacteriaceae family, have an acquired resistance against polymyxins, which is attributed to they possess plasmid-carried resistance genes (mcr-1 and its variants). So, there is an urgent need to develop new therapeutic strategies to target broad spectrum resistant spp. from Enterobacteriaceae family in response to the loss of the protective barrier of last-line antibiotics. Here, we report the adjuvant capacity of nordihydroguaiaretic acid (NDGA) for restoring the antibacterial activity of colistin against MCR-1-positive E. coli ZJ487 in vivo/in vitro. METHODS: A checkerboard assay, time-killing analysis, isobolograms, growth curves and inducible resistance test showed the effect of NDGA combined with colistin in vitro. TLC was used to detect the inhibitory effect of NDGA on MCR-1. Colony determination and hematoxylin and eosin (HE) staining were used to assess the synergistic effect of NDGA and colistin in mice. RESULTS: Our results showed that NDGA in combination with colistin showed a synergistic bactericidal action without inducing resistance. NDGA directly inhibited MCR-1 activity and resulted in measurable injury to the bacterial cell membrane to recover the antibacterial effect of colistin. Most importantly, NDGA in combination with colistin exhibited an in vivo synergistic effect in murine peritonitis infection models, as evidenced by the survival rate of MCR-1-positive E. coli ZJ487-infected mice which increased from 6.67 to 50.0%. CONCLUSION: Our study demonstrated that NDGA effectively rescues the efficiency of colistin against MCR-positive E. coli ZJ487 by simultaneously inhibiting both, the MCR activity and the injury to the cell membrane of bacteria.202235158237
64340.9988Effect of overexpression of small non-coding DsrA RNA on multidrug efflux in Escherichia coli. OBJECTIVES: Several putative and proven drug efflux pumps are present in Escherichia coli. Because many such efflux pumps have overlapping substrate spectra, it is intriguing that bacteria, with their economically organized genomes, harbour such large sets of multidrug efflux genes. To understand how bacteria utilize these multiple efflux pumps, it is important to elucidate the process of pump expression regulation. The aim of this study was to determine a regulator of the multidrug efflux pump in this organism. METHODS: We screened a genomic library of E. coli for genes that decreased drug susceptibility in this organism. The library was developed from the chromosomal DNA of the MG1655 strain, and then the recombinant plasmids were transformed into an acrB-deleted strain. Transformants were screened for resistance to various antibiotics including oxacillin. RESULTS: We found that the multidrug susceptibilities of the acrB-deleted strain were decreased by the overexpression of small non-coding DsrA RNA as well as by the overexpression of known regulators of multidrug efflux pumps. Plasmids carrying the dsrA gene conferred resistance to oxacillin, cloxacillin, erythromycin, rhodamine 6G and novobiocin. DsrA decreased the accumulation of ethidium bromide in E. coli cells. Furthermore, expression of mdtE was significantly increased by dsrA overexpression, and the decreased multidrug susceptibilities modulated by DsrA were dependent on the MdtEF efflux pump. CONCLUSIONS: These results indicate that DsrA modulates multidrug efflux through activation of genes encoding the MdtEF pump in E. coli.201121088020
626450.9988Multi-drug resistance pattern and genome-wide SNP detection in levofloxacin-resistant uropathogenic Escherichia coli strains. OBJECTIVES: Antibiotic treatment is extremely stressful for bacteria and has profound effects on their viability. Such administration induces physiological changes in bacterial cells, with considerable impact on their genome structure that induces mutations throughout the entire genome. This study investigated drug resistance profiles and structural changes in the entire genome of uropathogenic Escherichia coli (UPEC) strains isolated from six adapted clones that had evolved under laboratory conditions. METHODS: Eight UPEC strains, including two parental strains and six adapted clones, with different fluoroquinolone resistance levels originally isolated from two patients were used. The minimum inhibitory concentration (MIC) of 28 different antibiotics including levofloxacin was determined for each of the eight strains. In addition, the effects of mutations acquired with increased drug resistance in the levofloxacin-resistant strains on expression of genes implicated to be involved in drug resistance were examined. RESULTS: Of the eight UPEC strains used to test the MIC of 28 different antibiotics, two highly fluoroquinolone-resistant strains showed increased MIC in association with many of the antibiotics. As drug resistance increased, some genes acquired mutations, including the transcriptional regulator acrR and DNA-binding transcriptional repressor marR. Two strain groups with genetically different backgrounds (GUC9 and GFCS1) commonly acquired mutations in acrR and marR. Notably, acquired mutations related to efflux pump upregulation also contributed to increases in MIC for various antibiotics other than fluoroquinolone. CONCLUSIONS: The present results obtained using strains with artificially acquired drug resistance clarify the underlying mechanism of resistance to fluoroquinolones and other types of antibiotics.202438041251
575460.9987Efflux pump inhibitor CCCP to rescue colistin susceptibility in mcr-1 plasmid-mediated colistin-resistant strains and Gram-negative bacteria. OBJECTIVES: Efflux in bacteria is a ubiquitous mechanism associated with resistance to antimicrobials agents. Efflux pump inhibitors (EPIs) have been developed to inhibit efflux mechanisms and could be a good alternative to reverse colistin resistance, but only CCCP has shown good activity. The aim of our study was to identify CCCP activity in a collection of 93 Gram-negative bacteria with known and unknown colistin resistance mechanisms including isolates with mcr-1 plasmid-mediated colistin resistance. METHODS: Colistin MIC was evaluated with and without CCCP and the fold decrease of colistin MIC was calculated for each strain. In order to evaluate the effect of this combination, a time-kill study was performed on five strains carrying different colistin resistance mechanisms. RESULTS: Overall, CCCP was able to reverse colistin resistance for all strains tested. The effect of CCCP was significantly greater on intrinsically colistin-resistant bacteria (i.e. Proteus spp., Serratia marcescens, Morganella morganii and Providencia spp.) than on other Enterobacteriaceae (P < 0.0001). The same was true for bacteria with a heteroresistance mechanism compared to bacteria with other colistin resistance mechanisms (P < 0.0001). A time-kill study showed the combination was bacteriostatic on strains tested. CONCLUSIONS: These results suggest an efflux mechanism, especially on intrinsically resistant bacteria and Enterobacter spp., but further analysis is needed to identify the molecular support of this mechanism. EPIs could be an alternative for restoring colistin activity in Gram-negative bacteria. Further work is necessary to identify new EPIs that could be used in humans.201829718423
440770.9987A Simple Method for Assessment of MDR Bacteria for Over-Expressed Efflux Pumps. It is known that bacteria showing a multi-drug resistance phenotype use several mechanisms to overcome the action of antibiotics. As a result, this phenotype can be a result of several mechanisms or a combination of thereof. The main mechanisms of antibiotic resistance are: mutations in target genes (such as DNA gyrase and topoisomerase IV); over-expression of efflux pumps; changes in the cell envelope; down regulation of membrane porins, and modified lipopolysaccharide component of the outer cell membrane (in the case of Gram-negative bacteria). In addition, adaptation to the environment, such as quorum sensing and biofilm formation can also contribute to bacterial persistence. Due to the rapid emergence and spread of bacterial isolates showing resistance to several classes of antibiotics, methods that can rapidly and efficiently identify isolates whose resistance is due to active efflux have been developed. However, there is still a need for faster and more accurate methodologies. Conventional methods that evaluate bacterial efflux pump activity in liquid systems are available. However, these methods usually use common efflux pump substrates, such as ethidium bromide or radioactive antibiotics and therefore, require specialized instrumentation, which is not available in all laboratories. In this review, we will report the results obtained with the Ethidium Bromide-agar Cartwheel method. This is an easy, instrument-free, agar based method that has been modified to afford the simultaneous evaluation of as many as twelve bacterial strains. Due to its simplicity it can be applied to large collections of bacteria to rapidly screen for multi-drug resistant isolates that show an over-expression of their efflux systems. The principle of the method is simple and relies on the ability of the bacteria to expel a fluorescent molecule that is substrate for most efflux pumps, ethidium bromide. In this approach, the higher the concentration of ethidium bromide required to produce fluorescence of the bacterial mass, the greater the efflux capacity of the bacterial cells. We have tested and applied this method to a large number of Gram-positive and Gram-negative bacteria to detect efflux activity among these multi-drug resistant isolates. The presumptive efflux activity detected by the Ethidium Bromide-agar Cartwheel method was subsequently confirmed by the determination of the minimum inhibitory concentration for several antibiotics in the presence and absence of known efflux pump inhibitors.201323589748
576880.9987The resistance mechanism of Escherichia coli induced by ampicillin in laboratory. BACKGROUND: Multi-drug-resistant Escherichia coli poses a great threat to human health, especially resistant to ampicillin (AMP), but the mechanism of drug resistance is not very clear. PURPOSE: To understand the mechanism of resistance of E. coli to beta-lactam antibiotics by inducing drug resistance of sensitive bacteria in laboratory. METHODS: Clinical sensitive E. coli strain was induced into resistance strain by 1/2 minimum inhibitive concentration (MIC) induced trails of AMP. The drug resistance spectrum was measured by modified K-B susceptibility test. Whole-genome sequencing analysis was used to analyze primary sensitive strain, and resequencing was used to analyze induced strains. Protein tertiary structure encoded by the gene containing single nucleotide polymorphism (SNP) was analyzed by bioinformatics. RESULTS: After 315 hrs induced, the MIC value of E. coli 15743 reached to 256 µg/mL, 64 times higher than that of the sensitive bacteria. During the induction process, the bacterial resistance process is divided into two stages. The rate of drug resistance occurs rapidly before reaching the critical concentration of 32 µg/mL, and then the resistance rate slows down. Sequencing of the genome of resistant strain showed that E. coli 15743 drug-resistant strain with the MIC values of 32 and 256 µg/mL contained four and eight non-synonymous SNPs, respectively. These non-synonymous SNPs were distributed in the genes of frdD, ftsI, acrB, OmpD, marR, VgrG, and envZ. CONCLUSION: These studies will improve our understanding of the molecular mechanism of AMP resistance of E. coli, and may provide the basis for prevention and control of multi-drug-resistant bacteria and generation of new antibiotics to treat E. coli infection.201931571941
630090.9987Assessing the role of the RND efflux pump in metronidazole resistance of Helicobacter pylori by RT-PCR assay. INTRODUCTION: Metronidazole is a significant antibiotic used for eradication of Helicobacter pylori infections and it is of notice that metronidazole-resistant clinical isolates have been found in high rates worldwide. While the RND family of efflux pumps plays a central role in drug resistance among Gram-negative bacteria, this is questionable for H. pylori. METHODOLOGY: To understand whether TolC homologues of RND pumps contribute to metronidazole resistance in H. pylori isolates, expression of four TolC homologous genes of five resistant clinical isolates exposed to varying concentrations of metronidazole were evaluated by RT-PCR and transcriptional analysis. RESULTS: The results indicate that excess amounts of metronidazole are able to increase the expression level of these genes at the transcriptional stage. CONCLUSIONS: Therefore, it may be hypothesized that use of metronidazole in H. pyori infection can induce metronidazole resistance. Furthermore, the RND family of efflux pumps may contribute to metronidazole resistance in clinical isolates of H. pylori.201121389587
4705100.9987Upregulation of outer membrane porin gene ompC contributed to enhancement of azithromycin susceptibility in multidrug-resistant Escherichia coli. The outer membrane (OM) in gram-negative bacteria contains proteins that regulate the passive or active uptake of small molecules for growth and cell function, as well as mediate the emergence of antibiotic resistance. This study aims to explore the potential mechanisms for restoring bacteria to azithromycin susceptibility based on transcriptome analysis of bacterial membrane-related genes. Transcriptome sequencing was performed by treating multidrug-resistant Escherichia coli T28R with azithromycin or in combination with colistin and confirmed by reverse transcription-quantitative PCR (RT-qPCR). Azithromycin enzyme-linked immunosorbent assay (ELISA) test, ompC gene overexpression, and molecular docking were utilized to conduct the confirmatory research of the potential mechanisms. We found that colistin combined with azithromycin led to 48 differentially expressed genes, compared to azithromycin alone, such as downregulation of tolA, eptB, lpxP, and opgE and upregulation of ompC gene. Interestingly, the addition of colistin to azithromycin differentially downregulated the mph(A) gene mediating azithromycin resistance, facilitating the intracellular accumulation of azithromycin. Also, overexpression of the ompC elevated azithromycin susceptibility, and colistin contributed to further suppression of the Mph(A) activity in the presence of azithromycin. These findings suggested that colistin firstly enhanced the permeability of bacterial OM, causing intracellular drug accumulation, and then had a repressive effect on the Mph(A) activity along with azithromycin. Our study provides a novel perspective that the improvement of azithromycin susceptibility is related not only to the downregulation of the mph(A) gene and conformational remodeling of the Mph(A) protein but also the upregulation of the membrane porin gene ompC.IMPORTANCEUsually, active efflux via efflux pumps is an important mechanism of antimicrobial resistance, such as the AcrAB-TolC complex and MdtEF. Also, bacterial porins exhibited a substantial fraction of the total number of outer membrane proteins in Enterobacteriaceae, which are involved in mediating the development of the resistance. We found that the upregulation or overexpression of the ompC gene contributed to the enhancement of resistant bacteria to azithromycin susceptibility, probably due to the augment of drug uptakes caused and the opportunity of Mph(A) function suppressed by azithromycin with colistin. Under the combination of colistin and azithromycin treatment, OmpC exhibited an increased selectivity for cationic molecules and played a key role in the restoral of the antibiotic susceptibility. Investigations on the regulation of porin expression that mediated drug resistance would be important in clinical isolates treated with antibiotics.202438441474
210110.9987Development of antisense peptide-peptide nucleic acids against fluoroquinolone-resistant Escherichia coli. BACKGROUND: Fluoroquinolones (FQs) are potent and broad-spectrum antibiotics commonly used to treat MDR bacterial infections, but bacterial resistance to FQs has emerged and spread rapidly around the world. The mechanisms for FQ resistance have been revealed, including one or more mutations in FQ target genes such as DNA gyrase (gyrA) and topoisomerase IV (parC). Because therapeutic treatments for FQ-resistant bacterial infections are limited, it is necessary to develop novel antibiotic alternatives to minimize or inhibit FQ-resistant bacteria. OBJECTIVES: To examine the bactericidal effect of antisense peptide-peptide nucleic acids (P-PNAs) that can block the expression of DNA gyrase or topoisomerase IV in FQ-resistant Escherichia coli (FRE). METHODS: A set of antisense P-PNA conjugates with a bacterial penetration peptide were designed to inhibit the expression of gyrA and parC and were evaluated for their antibacterial activities. RESULTS: Antisense P-PNAs, ASP-gyrA1 and ASP-parC1, targeting the translational initiation sites of their respective target genes significantly inhibited the growth of the FRE isolates. In addition, ASP-gyrA3 and ASP-parC2, which bind to the FRE-specific coding sequence within the gyrA and parC structural genes, respectively, showed selective bactericidal effects against FRE isolates. CONCLUSIONS: Our results demonstrate the potential of targeted antisense P-PNAs as antibiotic alternatives against FQ-resistance bacteria.202337390375
215120.9987Non-antibiotics reverse resistance of bacteria to antibiotics. BACKGROUND: Most clinical isolates that exhibit a multi-drug resistant phenotype owe that resistance to over-expressed efflux pumps. Compounds that are efflux pump inhibitors (EPIs) reduce or reverse resistance to antibiotics to which the bacterial strain is initially resistant. We have evaluated non-antibiotics to reduce resistance of commonly encountered bacterial pathogens to antibiotics. MATERIALS AND METHODS: The effect of non-antibiotics on the susceptibility of bacteria to antibiotics was conducted by minimum inhibition concentration determinations of the antibiotic in the absence and presence of the non-antibiotic. RESULTS: Non-antibiotics such as chlorpromazine, amitryptiline and trans-chlorprothixene are shown to reduce or reverse resistance of a variety of bacteria to antibiotics. CONCLUSION: The results suggest that non-antibiotics may serve as adjuncts to conventional antibiotics for the therapy of problematic antibiotic infections caused by bacteria that owe their resistance to over-expressed efflux pumps.201020952744
6259130.9987Evidence of an efflux pump in Serratia marcescens. Spontaneous mutants resistant to fluoroquinolones were obtained by exposing Serratia marcescens NIMA (wild-type strain) to increasing concentrations of ciprofloxacin both in liquid and on solid media. Frequencies of mutation ranged from 10(-7) to 10(-9). Active expulsion of antibiotic was explored as a possible mechanism of resistance in mutants as well as changes in topoisomerase target genes. The role of extrusion mechanisms in determining the emergence of multidrug-resistant bacteria was also examined. Mutants resistant to high concentrations of fluoroquinolones had a single mutation in their gyrA QRDR sequences, whereas the moderate resistance in the rest of mutants was due to extrusion of the drug.200010990265
9759140.9987Rapid emergence of resistance to broad-spectrum direct antimicrobial activity of avibactam. Avibactam (AVI) is a diazabicyclooctane (DBO) β-lactamase inhibitor used clinically in combination with ceftazidime. At concentrations higher than those typically achieved in vivo, it also has broad-spectrum direct antibacterial activity against Enterobacterales strains, including metallo-β-lactamase-producing isolates, mediated by inhibition of penicillin-binding protein 2 (PBP2). This activity has some mechanistic similarities to that of more potent novel DBOs (zidebactam and nacubactam) in late clinical development. We found that resistance to AVI emerged readily, with a mutation frequency of 2 × 10(-6) to 8 × 10(-5). Whole-genome sequencing of resistant isolates revealed a heterogeneous mutational target that permitted bacterial survival and replication despite PBP2 inhibition, in line with prior studies of PBP2-targeting drugs. While such mutations are believed to act by upregulating the bacterial stringent response, we found a similarly high mutation frequency in bacteria deficient in components of the stringent response, although we observed a different set of mutations in these strains. Although avibactam-resistant strains had increased lag time, suggesting a fitness cost that might render them less problematic in clinical infections, there was no statistically significant difference in growth rates between susceptible and resistant strains. The finding of rapid emergence of resistance to avibactam as the result of a large and complex mutational target adds to our understanding of resistance to PBP2-targeting drugs and has potential implications for novel DBOs with potent direct antibacterial activity, which are being developed with the goal of expanding cell wall-active treatment options for multidrug-resistant gram-negative infections.IMPORTANCEAvibactam (AVI) is the first in a class of novel β-lactamase inhibitor antibiotics called diazabicyclooctanes (DBOs). In addition to its ability to inhibit bacterial β-lactamase enzymes that can destroy β-lactam antibiotics, we found that AVI had direct antibacterial activity, at concentrations higher than those used clinically, against even highly multidrug-resistant bacteria. This activity is the result of inhibition of the bacterial enzyme penicillin-binding protein 2 (PBP2). Resistance to other drugs that inhibit PBP2 occurs through mutations that involve upregulation of the bacterial "stringent response" to stress. We found that bacteria developed resistance to AVI at a high rate, as a result of mutations in stringent response genes. We also found that bacteria with impairments in the stringent response could still develop resistance to AVI through different mutations. Our findings indicate the importance of studying how resistance will emerge to newer, more potent DBOs in development and early clinical use.202540503840
6187150.9986Mechanisms of fluoroquinolone resistance: an update 1994-1998. Fluoroquinolone resistance is mediated by target changes (DNA gyrase and/or topoisomerase IV) and/or decreased intracellular accumulation. The genes (gyrA/gyrB/parC/parE) and proteins of DNA topoisomerase IV show great similarity, both at the nucleotide and amino acid sequence level to those of DNA gyrase. It has been shown that there are hotspots, called the quinolone resistance determining region (QRDR), for mutations within gyrA and parC. Based on the Escherichia coli co-ordinates, the hotspots most favoured for giving rise to decreased susceptibility and/or full resistance to quinolones are at serine 83 and aspartate 87 of gyrA, and at serine 79 and aspartate 83 for parC. Few mutations in gyrB or parE/grlB of any bacteria have been described. Efflux of fluoroquinolones is the major cause of decreased accumulation of these agents; for Staphylococcus aureus, the efflux pump involved in norfloxacin resistance is NorA, and for Streptococcus pneumoniae, PmrA. By analysis of minimum inhibitory concentration (MIC) data derived in the presence and absence of the efflux inhibitor reserpine, it has been shown that up to 50% of ciprofloxacin-resistant clinical isolates of S. pneumoniae may possess enhanced efflux. This suggests that efflux may be an important mechanism of clinical resistance in this species. In Pseudomonas aeruginosa, several efflux operons have been demonstrated genetically and biochemically. These operons are encoded by mex (Multiple EffluX) genes: mexAmexB-oprM, mexCD-OprJ system and mexEF-oprN system. The E. coli efflux pump is the acrAB-tolC system. Both the mar operon and the sox operon can give rise to multiple antibiotic resistance. It has been shown that mutations giving rise to increased expression of the transcriptional activators marA and soxS affect the expression of a variety of different genes, including ompF and acrAB. The net result is that expression of OmpF is reduced and much less drug is able to enter the cell; expression of acrAB is increased, enhancing efflux from the cell.199910553699
9783160.9986Synergism between Rifampicin and Cationic Polyurethanes Overcomes Intrinsic Resistance of Escherichia coli. Antibiotic-resistant Gram-negative bacteria are emergent pathogens, causing millions of infections worldwide. While there are several classes of antibiotics that are effective against Gram-positive bacteria, the outer membrane (OM) of Gram-negative bacteria excludes high-molecular-weight hydrophobic antibiotics, making these species intrinsically resistant to several classes of antibiotics, including polyketides, aminocoumarins, and macrolides. The overuse of antibiotics such as β-lactams has also promoted the spread of resistance genes throughout Gram-negative bacteria, including the production of extended spectrum β-lactamases (ESBLs). The combination of innate and acquired resistance makes it extremely challenging to identify antibiotics that are effective against Gram-negative bacteria. In this study, we have demonstrated the synergistic effect of outer membrane-permeable cationic polyurethanes with rifampicin, a polyketide that would otherwise be excluded by the OM, on different strains of E. coli, including a clinically isolated uropathogenic multidrug-resistant (MDR) E. coli. Rifampicin combined with a low-dose treatment of a cationic polyurethane reduced the MIC in E. coli of rifampicin by up to 64-fold. The compositions of cationic polyurethanes were designed to have low hemolysis and low cell cytotoxicity while maintaining high antibacterial activity. Our results demonstrate the potential to rescue the large number of available OM-excluded antibiotics to target normally resistant Gram-negative bacteria via synergistic action with these cationic polyurethanes, acting as a novel antibiotic adjuvant class.202134085824
6274170.9986Transcriptomics Reveals How Minocycline-Colistin Synergy Overcomes Antibiotic Resistance in Multidrug-Resistant Klebsiella pneumoniae. Multidrug-resistant Gram-negative bacteria are a rapidly growing public health threat, and the development of novel antimicrobials has failed to keep pace with their emergence. Synergistic combinations of individually ineffective drugs present a potential solution, yet little is understood about the mechanisms of most such combinations. Here, we show that the combination of colistin (polymyxin E) and minocycline has a high rate of synergy against colistin-resistant and minocycline-intermediate or -resistant strains of Klebsiella pneumoniae. Furthermore, using transcriptome sequencing (RNA-Seq), we characterized the transcriptional profiles of these strains when treated with the drugs individually and in combination. We found a striking similarity between the transcriptional profiles of bacteria treated with the combination of colistin and minocycline at individually subinhibitory concentrations and those of the same isolates treated with minocycline alone. We observed a similar pattern with the combination of polymyxin B nonapeptide (a polymyxin B analogue that lacks intrinsic antimicrobial activity) and minocycline. We also found that genes involved in polymyxin resistance and peptidoglycan biosynthesis showed significant differential gene expression in the different treatment conditions, suggesting possible mechanisms for the antibacterial activity observed in the combination. These findings suggest that the synergistic activity of this combination against bacteria resistant to each drug alone involves sublethal outer membrane disruption by colistin, which permits increased intracellular accumulation of minocycline.202235041511
6253180.9986The Contribution of Efflux Pumps in Mycobacterium abscessus Complex Resistance to Clarithromycin. The basis of drug resistance in Mycobacterium abscessus is still poorly understood. Nevertheless, as seen in other microorganisms, the efflux of antimicrobials may also play a role in M. abscessus drug resistance. Here, we investigated the role of efflux pumps in clarithromycin resistance using nine clinical isolates of M. abscessus complex belonging to the T28 erm(41) sequevar responsible for the inducible resistance to clarithromycin. The strains were characterized by drug susceptibility testing in the presence/absence of the efflux inhibitor verapamil and by genetic analysis of drug-resistance-associated genes. Efflux activity was quantified by real-time fluorometry. Efflux pump gene expression was studied by RT-qPCR upon exposure to clarithromycin. Verapamil increased the susceptibility to clarithromycin from 4- to ≥64-fold. The efflux pump genes MAB_3142 and MAB_1409 were found consistently overexpressed. The results obtained demonstrate that the T28 erm(41) polymorphism is not the sole cause of the inducible clarithromycin resistance in M. abscessus subsp. abscessus or bolletii with efflux activity providing a strong contribution to clarithromycin resistance. These data highlight the need for further studies on M. abscessus efflux response to antimicrobial stress in order to implement more effective therapeutic regimens and guidance in the development of new drugs against these bacteria.201931540480
6188190.9986Quinolone mode of action. Physical studies have further defined interactions of quinolones with their principal target, DNA gyrase. The binding of quinolones to the DNA gyrase-DNA complex suggests 2 possible binding sites of differing affinities. Mutations in either the gyrase A gene (gyrA) or the gyrase B gene (gyrB) that affect quinolone susceptibility also affect drug binding, with resistance mutations causing decreased binding and hypersusceptibility mutations causing increased binding. Combinations of mutations in both GyrA and GyrB have further demonstrated the contribution of both subunits to the quinolone sensitivity of intact bacteria and purified DNA gyrase. A working model postulates initial binding of quinolones to proximate sites on GyrA and GyrB. This initial binding then produces conformational changes that expose additional binding sites, possibly involving DNA. Quinolones also inhibit the activities of Escherichia coli topoisomerase IV (encoded by the parC and parE genes), but at concentrations higher than those inhibiting DNA gyrase. The patterns of resistance mutations in gryA and parC suggest that topoisomerase IV may be a secondary drug target in E. coli and Neisseria gonorrhoeae. In contrast, in Staphylococcus aureus these patterns suggest that topoisomerase IV may be a primary target of quinolone action. Regulation of expression of membrane efflux transporters may contribute to quinolone susceptibility in both Gram-positive and Gram-negative bacteria. The substrate profile of the NorA efflux transporter of S. aureus correlates with the extent to which the activity of quinolone substrates is affected by overexpression of NorA. In addition, the Emr transporter of E. coli affects susceptibility to nalidixic acid, and the MexAB OprK transport system of Pseudomonas aeruginosa affects susceptibility to ciprofloxacin.(ABSTRACT TRUNCATED AT 250 WORDS)19958549276