Drug Efflux Genes Research Articles

Molecular characterization and in-depth genomic analysis to unravel the pathogenic features of an environmental isolate Enterobacter sp. S-33.

Enterobacter species represent widely distributed opportunistic pathogens, commonly associated with plants and humans. In the present study, we performed a detailed molecular characterization as well as genomic study of a type VI secretion system (T6SS) bacterium belonging to member of the family Enterobacteriaceae and named Enterobacter sp. S-33. The comparative sequence analysis of the 16S rRNA gene showed that the strain was closely related to other Enterobacter species. The complete genome of the strain with a genome size of 4.6 Mbp and GC-content of 55.63% was obtained through high-quality sequencing. The genomic analysis with online tools unravelled the various genes belonging to the bacterial secretion system, antibiotic resistance, virulence, efflux pumps, etc. The isolate showed the motility behavior that contributes to Enterobacter persistence in a stressed environment and further supports infections. PCR amplification and further sequencing confirmed the presence of drug-efflux genes acrA, acrB, and outer membrane genes, viz. OmpA, OmpC, and OmpF. The cell surface hydrophobicity and co-aggregation assay against different bacterial strains illustrated its putative pathogenic nature. Genome mining identified various biosynthetic gene clusters (BGCs) corresponding to non-ribosomal proteins (NRPS), siderophore, and arylpolyene production. Briefly, genome sequencing and detailed characterization of environmental Enterobacter isolate will assist in understanding the epidemiology of Enterobacter species, and the further prevention and treatment of infectious diseases caused by these broad-host range species.

Antibiotic Resistance Mediated by Escherichia coli in Kuwait Marine Environment as Revealed through Genomic Analysis.

Antibiotic-resistance gene elements (ARGEs) such as antibiotic-resistance genes (ARGs), integrons, and plasmids are key to the spread of antimicrobial resistance (AMR) in marine environments. Kuwait's marine area is vulnerable to sewage contaminants introduced by numerous storm outlets and indiscriminate waste disposal near recreational beaches. Therefore, it has become a significant public health issue and warrants immediate investigation. Coliforms, especially Gram-negative Escherichia coli, have been regarded as significant indicators of recent fecal pollution and carriers of ARGEs. In this study, we applied a genome-based approach to identify ARGs' prevalence in E. coli isolated from mollusks and coastal water samples collected in a previous study. In addition, we investigated the plasmids and intl1 (class 1 integron) genes coupled with the ARGs, mediating their spread within the Kuwait marine area. Whole-genome sequencing (WGS) identified genes resistant to the drug classes of beta-lactams (blaCMY-150, blaCMY-42, blaCTX-M-15, blaDHA-1, blaMIR-1, blaOKP-B-15, blaOXA-1, blaOXA-48, blaTEM-1B, blaTEM-35), trimethoprim (dfrA14, dfrA15, dfrA16, dfrA1, dfrA5, dfrA7), fluroquinolone (oqxA, oqxB, qnrB38, qnrB4, qnrS1), aminoglycoside (aadA2, ant(3'')-Ia, aph(3'')-Ib, aph(3')-Ia, aph(6)-Id), fosfomycin (fosA7, fosA_6, fosA, fosB1), sulfonamide (sul1, sul2, sul3), tetracycline (tet-A, tet-B), and macrolide (mph-A). The MFS-type drug efflux gene mdf-A is also quite common in E. coli isolates (80%). The plasmid ColRNAI was also found to be prevalent in E. coli. The integron gene intI1 and gene cassettes (GC) were reported to be in 36% and 33%, respectively, of total E. coli isolates. A positive and significant (p < 0.001) correlation was observed between phenotypic AMR-intl1 (r = 0.311) and phenotypic AMR-GC (r = 0.188). These findings are useful for the surveillance of horizontal gene transfer of AMR in the marine environments of Kuwait.

Abstract 3660: Bone mechanics influence cancer stem cell formation in osteosarcoma

Abstract Osteosarcoma (OS) is the most common primary tumor of bone and is characterized by rapid bone remodeling accompanied by structural and mechanical heterogeneity across the tumor. Chemoresistance and recurrence of OS can be attributed to a subpopulation of OS cells known as cancer stem-like cells (OS-CSCs). It can be hypothesized that tumor niches possessing distinct structural and mechanical properties could be harboring different OS cell populations, and certain niches might be more conducive for OS-CSCs formation and maintenance. To evaluate the presence of OS-CSCs, mineralized collagen scaffolds mimicking heterogenous bone niches with distinct structural and mechanical properties were fabricated by changing collagen content and pore alignment and were cultured with the highly metastatic human OS cell line 143B. Scaffolds with 47% collagen by weight but different pore alignment were chosen for further analysis because they possessed different stiffness and topographical properties. Cytoskeletal changes, epigenetic changes, chemoresistance and chemoresistance-related pathways, and the levels of stemness genes were assessed in the 3D scaffold cultures. A consistent trend of OS-CSC phenotype was observed in the cell population grown in the softer bone niches (12 kPa) with aligned pores as compared to stiffer niche (31 kPa) with non-aligned pores. The cell population growing in softer, aligned scaffolds had a significantly higher expression of stemness genes (OCT4, NANOG, SOX2, ALDH1A1) and drug efflux gene ABCB1 and increased chemoresistance to doxorubicin and cisplatin. Epigenetic changes associated with cisplatin resistance in OS such as a decrease in methyl transferase EZH2 accompanied by the upregulation of LIF/Notch and PRKCA pathways was observed in cells grown in softer, aligned niches. Fluorescent imaging of actin organization showed rounder cells in the aligned niche indicative of the CSC phenotype, and stretched, elongated cells in the non-aligned niche indicative of a differentiated phenotype. Our study showed that the mechanical and structural properties of bone niches influence the formation of distinct OS cell populations. A softer niche with an aligned structure is more conducive for maintaining OS-CSCs. Citation Format: Zunaira Shoaib, Aleczandria S. Tiffany, Brendan Harley, Joseph Irudayaraj, Timothy M. Fan. Bone mechanics influence cancer stem cell formation in osteosarcoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3660.

Regulation of thymidylate synthase: an approach to overcome 5-FU resistance in colorectal cancer.

Thymidylate synthase is the rate-limiting enzyme required for DNA synthesis and overexpression of this enzyme causes resistance to cancer cells. Long treatments with 5-FU cause resistance to Thymidylate synthase targeting drugs. We have also compiled different mechanisms of drug resistance including autophagy and apoptosis, drug detoxification and ABC transporters, drug efflux, signaling pathways (AKT/PI3K, RAS-MAPK, WNT/β catenin, mTOR, NFKB, and Notch1 and FOXM1) and different genes associated with resistance in colorectal cancer. We can overcome 5-FU resistance in cancer cells by regulating thymidylate synthase by natural products (Coptidis rhizoma), HDAC inhibitors, mTOR inhibitors, Folate antagonists, and several other drugs which have been used in combination with TS inhibitors. This review is a compilation of different approaches reported for the regulation of thymidylate synthase to overcome resistance in colorectal cancer cells.

Transitioning pre-clinical glioblastoma models to clinical settings with biomarkers identified in 3D cell-based models: A systematic scoping review.

Glioblastoma (GBM) remains incurable despite the overwhelming discovery of 2-dimensional (2D) cell-based potential therapeutics since the majority of them have met unsatisfactory results in animal and clinical settings. Incremental empirical evidence has laid the widespread need of transitioning 2D to 3-dimensional (3D) cultures that better mimic GBM's complex and heterogenic nature to allow better translation of pre-clinical results. This systematic scoping review analyses the transcriptomic data involving 3D models of GBM against 2D models from 22 studies identified from four databases (PubMed, ScienceDirect, Medline, and Embase). From a total of 499 genes reported in these studies, 313 (63%) genes were upregulated across 3D models cultured using different scaffolds. Our analysis showed that 4 of the replicable upregulated genes are associated with GBM stemness, epithelial to mesenchymal transition (EMT), hypoxia, and migration-related genes regardless of the type of scaffolds, displaying close resemblances to primitive undifferentiated tumour phenotypes that are associated with decreased overall survival and increased hazard ratio in GBM patients. The upregulation of drug response and drug efflux genes (e.g. cytochrome P450s and ABC transporters) mirrors the GBM genetic landscape that contributes to in vivo and clinical treatment resistance. These upregulated genes displayed strong protein-protein interactions when analysed using an online bioinformatics software (STRING). These findings reinforce the need for widespread transition to 3D GBM models as a relatively inexpensive humanised pre-clinical tool with suitable genetic biomarkers to bridge clinical gaps in potential therapeutic evaluations.

A saponin-polybromophenol antibiotic (CU1) from Cassia fistula Bark Against Multi-Drug Resistant Bacteria Targeting RNA polymerase

BackgroundGradual increase of multidrug resistant infections is a threat to the human race as MDR plasmids have acquired.>10 mdr and drug efflux genes to inactivate antibiotics. Plants secret anti-metabolites to retard growth of soil and water bacteria and are ideal source of antibiotics. PurposePurpose of the study is to discover an alternate phyto-drug from medicinal plants of India that selectively kills MDR bacteria. MethodsMDR bacteria isolated from Ganga river water, milk, chicken meat and human hair for testing phyto-extracts. Eighty medicinal plants were searched and six phyto-extracts were selected having good antibacterial activities as demonstrated by agar-hole assays giving 15 ​mm or greater lysis zone. Phyto-extracts were made in ethanol or methanol (1:5 w/v) for overnight and were concentrated. Preparative TLC and HPLC were performed to purify phytochemical. MASS, NMR, FTIR methods were used for chemical analysis of CU1. In vitro RNA polymerase and DNA polymerase assays were performed for target identification. ResultsCU1 belongs to a saponin bromo-polyphenol compound with a large structure that purified on HPLC C18 column at 3min. CU1 is bacteriocidal but three times less active than rifampicin in Agar-hole assay. While in LB medium it shows greater than fifteen times poor inhibitor due to solubility problem. CU1 inhibited transcription from Escherichia coli as well as Mycobacterium tuberculosis RNA Polymerases. Gel shift assays demonstrated that CU1 interferes at the open promoter complex formation step. On the other hand CU1 did not inhibit DNA polymerase. ConclusionPhyto-chemicals from Cassia fistula bark are abundant, less toxic, target specific and may be a safer low cost drug against MDR bacterial diseases.

Novel pharmacological approach for the prevention of multidrug resistance (MDR) in a human leukemia cell line

BackgroundDrug resistance mechanisms are the regulatory factors associated with drug metabolism and drug transport to inward and outward of the target cells. Maybridge fragment (MBF) library is a collection of pharmacophore rich compounds having affinity with membrane transporters. This study has been designed to evaluate the efficacy of MBFs in overcoming the leukemic cells’ resistance to imatinib. MethodsImatinib resistant cells (K562-R) were prepared using myelogenous leukemia cell line (K562) by titration method. The four MBFs were prioritized for determining their effect on imatinib resistance. The cells were treated with imatinib and MBFs and the MTT assay was performed to evaluate the efficacy of MBFs in enhancing the imatinib mediated cell death. The transcript levels of Bcr-Abl1 gene and efflux transporter genes were determined by RT-qPCR analysis. ResultsThe MBFs enhanced the imatinib mediated cell death of K562-R cells. There was also a significant decrease in the mRNA levels of the major drug efflux genes (ABCB1, ABCB10, ABCC1 and ABCG2) when treated with a combination of imatinib and MBF in comparison to imatinib treatment alone. ConclusionThe drug efflux is one of the mechanisms of multidrug resistance in cancer cells and the MBFs used in this study were all found to significantly overcome the imatinib resistance by limiting the expression of efflux genes. This study, therefore, highlights the potential of Maybridge compounds in treating the drug resistant leukemia.

Mechanism of multi-resistant bacterial pathogenesis: MDR genes are not so deadly unless plasmid-mediated toxin, virulence and regulatory genes are activated

<em>mdr</em> genes in association with many drug efflux and metal efflux genes are creating pathogenesis due to antibiotic void. However, most dangerous step occurred when R-plasmids and integrons (~2-9kb) were combined with F’-conjugative plasmid (62.5kb) creating large <em>mdr</em> conjugative plasmids that easily donated 6-15 <em>mdr</em> genes to gut microbiota as well as environmental bacteria.

Molecular mechanism of azoles resistant Candida albicans in a patient with chronic mucocutaneous candidiasis

BackgroundMore and more azole-resistant strains emerged through the development of acquired resistance and an epidemiological shift towards inherently less susceptible species. The mechanisms of azoles resistance of Candida albicans is very complicated. In this study, we aim to investigate the mechanism of azole-resistant C. albicans isolated from the oral cavity of a patient with chronic mucocutaneous candidiasis (CMC).Case presentationCMC diagnosis was given based on clinical manifestations, laboratory test findings and gene sequencing technique. Minimum inhibitory concentration (MIC) of the fungal isolate, obtained from oral cavity termed as CA-R, was obtained by in vitro anti-fungal drugs susceptibility test. To further investigate the resistant mechanisms, we verified the mutations of drug target genes (i.e. ERG11 and ERG3) by Sanger sequencing, and verified the over-expression of ERG11 and drug efflux genes (i.e. CDR1 and CDR2) by RT-PCR. A heterozygous mutation of c.1162A > G resulting in p.K388E was detected in STAT1 of the patient. The expression of CDR1 and CDR2 in CA-R was 4.28-fold and 5.25-fold higher than that of type strain SC5314, respectively.ConclusionsUp-regulation of CDR1 and CDR2 was mainly responsible for the resistance of CA-R. For CMC or other immunodeficiency patients, drug resistance monitoring is necessary.

α2δ1 may be a potential marker for cancer stem cell in laryngeal squamous cell carcinoma.

Cancer stem cells (CSCs) have the ability to dictate tumor initiation, recurrence, and metastasis. Here, we examined the expression of a21 in laryngeal cancer tissues and further determined the effect of 21 on the migratory ability and tumorigenicity of laryngeal cancer cells. Immunofluorescence staining revealed that 21 was positive in 13 (13/16, 81.25%) cases in laryngeal squamous cell carcinoma (LSCC) tissues, 7 (7/16, 43.75%) cases in paracancerous tissues and only 2 (2/16, 12.5%) cases in normal tumor tissues. Our quantitative RT-PCR assays further showed that 21 LSCC cells expressed significantly higher levels of stem cell-associated genes and drug efflux and resistance genes versus21 cells. Sphere-forming assays demonstrated higher sphere-forming efficiency in the 21versus21 subpopulation. Our Matrigel assays showed that 21 cells exhibited significantly greater invasive and migratory ability than 21 cells. Furthermore, the percentage of purified 21 in TU686 and TU212 cells treated cisplatin or paclitaxel was significantly higher than that of the control group. Tumor xenograft assays revealed that the tumorigenicity of 21 cells was much higher than 21 cells. In conclusion, a 21 subpopulation with CSC-like property was present in laryngeal cancer and possessed high self-renewal activity and was sufficient for tumor growth, differentiation, migration, invasion, and chemotherapeutic resistance. They could represent a promising therapeutic target for LSCC.

Poor Correlation of Diversified MDR Genes in Gonococci Plasmids: Does Alteration in Chromosomal DEGs, PBP2 and Target Mutations Sufficient to Widespread Multi-Resistance in Neisseria gonorrhoeae?

Spread of ceftriaxone and ciprofloxacin resistant gonococci diseases demand new drug development as research have contradicted potent carbapenem and aminoglycoside antibiotics against Neisseria gonorrhoeae infections. Pubmed and GenBank analysis demonstrated only bla TEM and tetM genes present in N. gonorrhoeae plasmids where as in most MDR Enterobacteriaceae, hundred diversified beta-lactamase genes (blaOXA, blaCTX-M, blaCMY and blaNDM1) as well as many drug modified genes (aacA1/C1, catB3, aph, strA/B, sul1/2, aad, aph and aac(6’)-1b) are frequent in plasmids and chromosome. Thus existing knowledge on gonococci mdr genes is limited and merely few chromosomal drug efflux genes (DEGs=ermAB, mtrCDE, macAB etc.) and penicillin binding proteins (PBPs=ponA and penA) have assigned as cause of multi-resistance. It appeared that N. gonorrhoeae had limited life cycle outside the host limiting conjugation with other MDR-bacteria to acquire mdr genes easily. BLAST-search confirmed that every MDR N. gonorrhoeae genome did carry mtrD RND transporter gene linked to mtrC outer membrane efflux gene (MFS) similar to P. aeruginosa mexAB-family transporters. Further, macA/B transporters are involved in macrolide drug efflux and many mutations in penA, gyrA, mtrR and porB genes are maximum in MDR strains although mtrF and norA efflux genes are infrequent. We argue that plasmid mediated multi-resistance in gonococcal diseases needs to be reinvestigated and mutation theory (penA, gyrA, mtrR) may not sufficient to prove the worldwide spread of multi-drug resistant STDs.

Rapid multiplexed phenotypic screening identifies drug resistance functions for three novel efflux pumps in Acinetobacter baumannii.

Drug efflux pumps are one of the key machineries in bacterial drug resistance. Although quite a few of these transport systems have been functionally characterized in various organisms, due to large-scale genome sequencing efforts and improved prediction pipelines there are increasing numbers of putative drug efflux genes annotated. For phenotype identification of the proteins encoded by these genes, we developed a novel high-throughput phenotype screening strategy and demonstrated its utility in identifying phenotypes for putative efflux systems encoded by the human pathogen Acinetobacter baumannii. Seventeen putative drug efflux systems from A. baumannii were heterologously expressed in Escherichia coli. For rapid and economical phenotype screening we employed a combination of multiplexed Biolog Phenotype Microarrays and quantitative PCR. Using this method we screened these putative drug efflux pumps against 240 antimicrobial conditions, equating to 4080 simultaneous phenotypic tests. Of the 17 putative drug efflux systems, phenotypes were confirmed for two pumps and novel drug resistance phenotypes were identified for three new A. baumannii drug transporters, which exemplified the power of this method as a high-throughput screening technique. One of the phenotypically characterized putative drug efflux systems was classified within the ATP-binding cassette superfamily of transport proteins and represents the first drug resistance protein characterized from this superfamily in A. baumannii. The remaining two proteins were members of the major facilitator superfamily of efflux pumps. This method has broad potential for high-throughput phenotype characterization of putative drug efflux systems in a range of organisms.

A Pharmacogenetic Study of the NCIC CTG Clinical Trial My.10: Single Nucleotide Polymorphisms, Prognosis, and Predicting Benefit from IMiD® Compound Maintenance Therapy Following Autologous Stem Cell Transplant for Multiple Myeloma

Introduction: In multiple myeloma, randomized trials of maintenance therapy using thalidomide or lenalidomide following autologous transplant (ASCT) demonstrated prolonged progression-free survival (PFS), but overall survival benefit was inconsistent. The MY.10 trial (n=332) demonstrated improved PFS with thalidomide-prednisone maintenance therapy, but quality of life was inferior and overall survival was not improved. As a randomized trial with a no-treatment control arm and biospecimen collection, MY.10 provides a unique opportunity to identify predictors of benefit from therapy that could be used to personalize treatment. Immunomodulatory drug action is mediated in part through binding to cereblon (CRBN) and downregulation of IRF4. Candidate single nucleotide polymorphisms (SNPs) were selected from the CRBN/IRF4 pathway and other genes previously associated with myeloma prognosis, drug response and toxicity from literature review. The aim of this study was to investigate associations between candidate SNPs and benefit from immunomodulatory compound-based maintenance therapy, as well as prognostic impact.Methods: Genomic DNA was extracted from samples preserved in Trizol¨. SNPs were genotyped using TaqMan¨ genotyping assays on the ViiA7 qPCR platform. Analysis was performed on 187 patients with available samples and clinical data (86 in treatment arm; 101 in observation arm). Cox regression models were performed using SAS clinical 2.0 for prognostic impact of a single SNP on PFS, assessed with and without adjusted covariates (age, stage, performance status and response to ASCT). In treatment benefit analysis, PFS was modeled with genotype, treatment assignment and their interaction term.Results: SNPs with significant prognostic impact for PFS in all 187 patients were found in CRBN (rs1672753) (HR 0.59, 95%CI 0.4-0.86; p=0.006) and the following SNPs which had been found to be prognostic in prior studies were validated: CYP1A1 (rs1048943) (HR 1.98, 95%CI 1.19-3.27; p=0.008), CYP1B1 (rs1056836) (HR 0.72, 95%CI 0.52-0.99; p=0.043), and trend toward significance for SNP in CYP1A2 (rs2069514) (HR 2.02, 95%CI 0.98-4.15; p=0.057). Of these, only the CYP1A1 SNP was found to be possibly predictive of greater benefit from maintenance therapy. A SNP in ABCA1 (rs363717), previously associated with thalidomide-induced neuropathy,‎ was prognostic in this study (HR 1.44, 95%CI 1.03-2.02; p=0.033) but not predictive of treatment benefit. Table 1 lists SNPs associated with a differential level of benefit from maintenance therapy, including SNPs in FAM179a and ICAM1 that were possibly associated with harm from maintenance therapy.Table 1SNPs and treatment interaction with significant impact on PFS. HR represent hazard ratio of treatment versus observation for a given genotype group. Asterisk Indicates trend toward significance.WildtypeHeterozygote & mutantp-value interactionGenedbSNP IDSNPHR95% CIHR95% CIFAM179Ars1053667T>C0.460.33, 0.662.280.78, 6.650.003ICAM1rs1799969G>A0.510.36, 0.731.750.83, 3.700.007CASP3rs1049216A>G0.820.54, 1.250.410.25, 0.690.029IRF4rs12203592C>T0.690.47, 1.020.380.21, 0.690.062*CYP1A1rs1048943A>G0.620.44, 0.870.110.02, 0.520.079*Conclusion: Previously identified SNPs in drug metabolism and drug efflux genes were validated to be prognostic in this cohort. The prognostic but not predictive significance of a SNP in CRBN suggests a possible role for CRBN in multiple myeloma disease biology independent of immunomodulatory therapy. SNPs predictive of differing degrees of benefit from immunomodulatory maintenance were found in genes involved in immunomodulatory activation, drug action and cell adhesion mediated drug resistance; SNPs in FAM179A and ICAM1 were possibly associated with harm from thalidomide maintenance and could potentially be used to identify patients unsuitable for immunomodulatory maintenance therapy. These results may be applicable to lenalidomide and pomalidomide, since immunomodulatory compounds exhibit similar chemical structures and mechanisms of action. Validation of these SNPs in prospective clinical trials involving other immunomodulatory can test this hypothesis. Further studies are needed to confirm our findings. DisclosuresOff Label Use: thalidomide and prednisone maintenance for multiple myeloma. Bahlis:Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Amgen: Consultancy; Johnson & Johnson: Speakers Bureau; Johnson & Johnson: Consultancy; Johnson & Johnson: Research Funding. Song:Celgene Canada: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. White:Celgene Canada: Honoraria, Research Funding. Chen:Celgene: Consultancy, Honoraria, Research Funding. Seftel:Celgene: Honoraria, Research Funding. Howsen-Jan:Celgene: Honoraria, Research Funding. Reece:Amgen: Honoraria; Bristol-Myers Squibb: Research Funding; Merck: Research Funding; Novartis: Honoraria, Research Funding; Onyx: Consultancy; Millennium Takeda: Research Funding; Lundbeck: Honoraria; Otsuka: Research Funding; Janssen-Cilag: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding. Shepherd:Celgene: Honoraria, Research Funding. Chen:Celgene: Honoraria, Research Funding. Djurfeldt:Celgene: Research Funding. Reiman:Soricimed Biopharma Inc: Consultancy, Other: Scientific Advisory Board for Soricimed.

Overproduction of the MtrCDE efflux pump in Neisseria gonorrhoeae produces unexpected changes in cellular transcription patterns.

The global consequence of drug efflux gene overexpression in bacteria has not been specifically analyzed because strains showing high-level expression typically have mutations in genes encoding regulatory proteins that control other genes. Results from a transcriptional profiling study performed with a strain of Neisseria gonorrhoeae that is capable of high-level transcription of the mtrCDE efflux pump operon independently of control by cognate regulatory proteins revealed that its overexpression has ramifications for systems other than drug efflux.

Correlation of ciprofloxacin resistance with the AdeABC efflux system in Acinetobacter baumannii clinical isolates.

BackgroundAcinetobacter baumannii is one of the most important pathogens capable of colonization in burn patients, leading to drug-resistant wound infections. This study evaluated the distribution of the AdeABC efflux system genes and their relationship to ciprofloxacin resistance in A. baumannii isolates collected from burn patients.MethodsA total of 68 A. baumannii clinical strains were isolated from patients hospitalized in Motahari Burns Center in Tehran, Iran. Ciprofloxacin susceptibility was tested by the disk diffusion and agar dilution methods. PCR amplification of the adeRS-adeB drug efflux genes was performed for all resistant and susceptible isolates. To assess the role of the drug efflux pump in ciprofloxacin susceptibility, carbonyl cyanide 3-chlorophenylhydrazone (CCCP) was used as an efflux pump inhibitor (EPI).ResultsApproximately 95.6% of the Acinetobacter isolates were resistant to ciprofloxacin, with minimum inhibitory concentration (MIC) values ranging from 4 to ≥128 µg/mL. The susceptibility of 86.1% of the resistant isolates increased by factors of 2 to 64 in the presence of CCCP. All resistant isolates were positive for the adeRS-adeB genes, and 73.2% of them had mutations in the AdeRS regulatory system.ConclusionsThe results showed that AdeABC genes are common in A. baumannii, which might be associated with ciprofloxacin non-susceptibility, as indicated by the observed linkage to the presence of the genes essential for the activity of the AdeABC, several single mutations occurring in the adeRS regulatory system, and an increase of ciprofloxacin susceptibility in the presence of a CCCP EPI.

Functional linkage between genes that regulate osmotic stress responses and multidrug resistance transporters: challenges and opportunities for antibiotic discovery.

All cells need to protect themselves against the osmotic challenges of their environment by maintaining low permeability to ions across their cell membranes. This is a basic principle of cellular function, which is reflected in the interactions among ion transport and drug efflux genes that have arisen during cellular evolution. Thus, upon exposure to pore-forming antibiotics such as amphotericin B (AmB) or daptomycin (Dap), sensitive cells overexpress common resistance genes to protect themselves from added osmotic challenges. These genes share pathway interactions with the various types of multidrug resistance (MDR) transporter genes, which both preserve the native lipid membrane composition and at the same time eliminate disruptive hydrophobic molecules that partition excessively within the lipid bilayer. An increased understanding of the relationships between the genes (and their products) that regulate osmotic stress responses and MDR transporters will help to identify novel strategies and targets to overcome the current stalemate in drug discovery.

A primary investigation on the isoniazid-induced alterations in efflux gene expression among the isoniazid resistant Mycobacterium tuberculosis clinical isolates

To detect the changes on the expression of putative drug efflux genes caused by isoniazid-inducement in single resistance to the isoniazid Mycobacterium tuberculosis (M. tuberculosis) clinical isolates, for exploring the putative efflux genes which causing M. tuberculosis isoniazid resistance as well as the mechanism related to high expression of the putative efflux genes. We selected 35 M. tuberculosis clinical isolates which were only resistant to isoniazid as well as 10 sensitive M. tuberculosis clinical isolates and using H37Rv as control. Each strain was cultured in 7H9 liquid medium without isoniazid and with subinhibitory isoniazid concentration (1/4 MIC) induction. After RNA extraction and reverse transcription, real-time PCR was conducted to assess the expression changes of 27 putative drug efflux pump genes with formula 2(-ΔΔCT) to calculate the expression of each putative drug efflux pump genes. Of the 27 putative genes, 13 of them were expressed at high level. High expression of Rv1258c gene had the maximum number of 6 strains, followed by high expression of Rv0849 and Rv2265 which both had 5 strains. Fourteen strains (40.00%) out of the 35 strains had high expression pump genes. Six strains (17.14%) had only one highly expressed putative efflux pump gene. Eight strains (22.86%) had two or more highly expressed putative efflux pump genes, including two, four, five, seven genes that highly expressed in 4, 2, 1, 1 strains respectively. For the 27 putative genes, ten sensitive strains and H37Rv did not show highly expressed genes. Rv1258c, Rv2265, Rv0849, etc. genes might be the putative efflux pumps genes of M. tuberculosis resistant to isoniazid. Isoniazid might serve as the inducer of M. tuberculosis part putative efflux pump genes, inducing activation and causing high expression of these putative efflux pump genes.

Emergence of a novel GyrA variant from a strain of multidrug-resistant Klebsiella pneumoniae isolated from in China

A strain of Klebsiella pneumoniae (NB029) was positive for blaTEM (beta-lactamase gene), aph(3’)Ⅰ(aminoglycoside modifying enzyme gene), gyrA (quinolone resistance gene), trbC (genetic marker of plasmids), tnp513, IS26, IS903 (genetic markers of transposons and insertion sequences), intⅠ1 (genetic marker of integrons), qacE△1 (drug efflux gene) by PCR assays. So these positive genes confer multidrug-resistant phenotype. And the presence of gyrA, confirmed as a novel variant (Genbank accession number: JN232083), was determined by sequencing and Blastsguin algorithm. The double mutations at codon 83 and codon 87 in the quinolone resistance-determining region of the gyrA gene lead to high level quinolone resistance.

Impact of Hfq on the Intrinsic Drug Resistance of Salmonella Enterica Serovar Typhimurium

Salmonella enterica is an important enteric pathogen, and its various serovars cause both systemic and intestinal diseases in humans and domestic animals. The emergence of multidrug-resistant strains of Salmonella, leading to increased morbidity and mortality, has further complicated its management. Hfq is an RNA chaperon that mediates the binding of small RNAs to mRNA and assists in post-transcriptional gene regulation in bacteria. Although Hfq is related to important phenotypes including virulence in Salmonella, its role in the drug resistance of this organism is unknown. The aim of this study was to investigate the role of Hfq in intrinsic drug resistance of S. enterica serovar Typhimurium. hfq Mutant was susceptible to acriflavine. Although there is a relationship between the production of the AcrB multidrug efflux pump and Hfq in Escherichia coli, the deletion of the drug efflux acrB did not impair the effect of hfq deletion on Salmonella susceptibility. In contrast, the deletion of another drug efflux gene, smvA, impaired the effect of hfq deletion on acriflavine susceptibility. These results indicate that Hfq regulates the intrinsic drug resistance, and it may influence drug susceptibility by regulating SmvA in Salmonella.

Physiological Role of Bacterial Multidrug Efflux Pumps

Since the discovery of antibiotics, the battle between humans and drug resistant bacteria has never stopped. Bacteria have developed various ways to resist the toxic effects of antibiotics and other drugs. Multidrug efflux pumps are integral membrane proteins that utilize cellular energy to extrude antibiotics or biocides actively out of the cell. In this symposium, I first introduce the post-genomic approach to analyze all putative drug efflux genes. Next, I discuss the regulation of drug efflux pumps responding to environmental signals. I also introduce the physiological roles of drug efflux pumps in virulence, which is an ongoing research area. Multidrug efflux pumps have greater clinical relevance than has previously been thought, because there is now accumulating evidence that certain classes of efflux pumps not only confer resistance to drugs used in therapy but also have a role in bacterial pathogenicity.