Rv1218c, an ABC transporter of Mycobacterium tuberculosis with implications in drug discovery

Efflux systems are important in determining the efficacy of antibiotics used in the treatment of bacterial infections. In the last decade much attention has been paid to studying the efflux pumps of mycobacteria. New classes of compounds are under investigation for development into potential candidate drugs for the treatment of tuberculosis. Quite often, these have poor bactericidal activities but exhibit excellent target (biochemical) inhibition. Microarray studies conducted in our laboratories for deciphering the mode of action of experimental drugs revealed the presence of putative ABC transporters. Among these transporters, Rv1218c was chosen for studying its physiological relevance in mediating efflux in Mycobacterium tuberculosis. A ΔRv1218c mutant of M. tuberculosis displayed a 4- to 8-fold increase in the inhibitory and bactericidal potency for different classes of compounds. The MICs and MBCs were reversed to wild-type values when the full-length Rv1218c gene was reintroduced into the ΔRv1218c mutant on a multicopy plasmid. Most of the compound classes had significantly better bactericidal activity in the ΔRv1218c mutant than in the wild-type H37Rv, suggesting the involvement of Rv1218c gene product in effluxing these compounds from M. tuberculosis. The implication of these findings on tuberculosis drug discovery is discussed.     

Contribution of the Rv2333c efflux pump (the Stp protein) from Mycobacterium tuberculosis to intrinsic antibiotic resistance in Mycobacterium bovis BCG

OBJECTIVES: To characterize the efflux pump encoded by the gene Rv2333c from Mycobacterium tuberculosis, and assess its contribution to intrinsic antibiotic resistance using Mycobacterium bovis BCG as a model organism. METHODS: Firstly, the Rv2333c gene was expressed from a multicopy plasmid in M. bovis BCG. Secondly, the gene was inactivated in the chromosome of M. bovis BCG. Antibiotic susceptibility tests and tetracycline uptake/efflux experiments were carried out with the strains mentioned above. RESULTS: When the Rv2333c gene was inactivated in the M. bovis BCG chromosome, there was a decrease in the MIC values of spectinomycin and tetracycline, and an increase in [3H]tetracycline accumulation. When the Rv2333c gene was cloned into a multicopy plasmid, there was an increase in the MIC values of spectinomycin and tetracycline, and a decrease in [3H]tetracycline accumulation. These results indicate that both antibiotics are substrates of the Rv2333c efflux pump, which has been named Stp, for Spectinomycin Tetracycline efflux Pump. CONCLUSIONS: The Rv2333c efflux pump (Stp protein) of M. tuberculosis contributes to intrinsic spectinomycin and tetracycline resistance.     

结核分枝杆菌抗原Rv2654c、Rv1985c和Rv3868的克隆表达及血清诊断学初步评价

目的 评价结核分枝杆菌蛋白抗原Rv2654c、Rv1985c和Rv3868的血清诊断价值和潜在应用前景。方法 以结核分枝杆菌H37Rv标准株全基因组DNA为模板扩增得到Rv2654c、Rv1985c和Rv3868基因的完整序列, 并与表达载体pET-32a构建重组质粒。原核表达Rv2654c、Rv1985c和Rv3868蛋白, 利用亲和层析的方法进行纯化。采用棋盘滴定的方法, 确定各抗原的酶联免疫吸附试验(ELISA)最佳反应条件, 并应用190份血清进行血清IgG抗体检测, 结合受试者工作特征曲线(ROC)对其诊断效能进行分析和评价。通过ROC计算各抗原组合的诊断效能, 确定最佳组合方案。结果 成功构建了重组蛋白, 对重组后的片段进行测序, 经BLAST比对与目的基因完全一致, 且能够稳定表达。对经纯化后的3种蛋白进行ELISA检测, 经统计学分析, Rv2654c、Rv1985c和Rv3868抗原的诊断效能分别达到73.16%、56.84%和71.05%。结合ROC得到最佳的抗原组合方案为Rv2654c+Rv3868, 其敏感性、特异性和诊断效能分别达到78.95%、72.63%和75.79%。结论 结核分枝杆菌重组抗原Rv2654c、Rv1985c和Rv3868具有作为结核病诊断抗原的潜力, 可以作为结核病免疫学快速诊断的候选蛋白。抗原组合Rv2654c+Rv3868具有较高的诊断效能, 有较好的潜在应用价值。     

EfrAB, an ABC multidrug efflux pump in Enterococcus faecalis

A DNA fragment responsible for resistance to antimicrobial agents was cloned from the chromosomal DNA of Enterococcus faecalis ATCC 29212 by using drug-hypersensitive mutant Escherichia coli KAM32 as a host cell. Cells of E. coli KAM32 harboring a recombinant plasmid (pAEF82) carrying the DNA fragment became resistant to many structurally unrelated antimicrobial agents, such as norfloxacin, ciprofloxacin, doxycycline, acriflavine, 4',6-diamidino-2-phenylindole, tetraphenylphosphonium chloride, daunorubicin, and doxorubicin. Since the sequence of the whole genome of E. faecalis is known, we sequenced several portions of the DNA insert in plasmid pAEF82 and identified two open reading frames within the insert. We designated the genes efrA and efrB. A search of the deduced amino acid sequences of EfrA and EfrB revealed that they are similar to each other and that they belong to the ATP-binding cassette (ABC) family of multidrug efflux transporters. Transformed E. coli KAM32 cells harboring efrAB showed energy-dependent efflux of acriflavine. The efflux activity was inhibited by reserpine, verapamil, and sodium-o-vanadate, known inhibitors of ABC efflux pumps.     

结核分枝杆菌Rv1884c和Rv0867c基因的克隆表达及其促生长作用的研究

目的 构建结核分枝杆菌Rv1884c和Rv0867c基因的原核表达质粒,获得结核分枝杆菌Rvl884c和Rv0867c基因的表达蛋白,并初步研究其促生长作用.方法 制备结核分枝杆菌基因组DNA,采用PCR技术扩增目的 基因片段;将2个片段分别克隆入克隆载体pGEx-4T-1和pUC19,再分别克隆入原核表达载体pGEX-4T-1和pPRO-EXHT,经序列测定证实正确后,再经异丙基硫代-β-D半乳糖苷(IPTG)诱导表达GST标记的Rv1884c融合蛋白和His标记的Rv0867c融合蛋白;用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)分析重组蛋白的相对分子质量大小及表达形式.结果 成功扩增出了结核分枝杆菌Rv1884c和Rv0867c基因,构建了具有正确基因序列的质粒载体pGEX-4T-1-Rv1884c和pPRO-EXHT-Rv0867c,转化人大肠杆菌DH5α中经诱导产生高水平的表达产物.经SDS分析,在相对分子质量为45 000和80 000处出现新生蛋白带,凝胶薄层扫描检测表达量分别约占菌体蛋白的18.3%和23.7%.用GSTrap FF亲和层析柱和Ni2+-NTA纯化柱进行蛋白纯化,并研究这两种蛋白对藤黄微球菌、BCG和结核分枝杆菌H37Rv的促生长作用.结论 成功克隆了结核分枝杆菌Rv1884c和Rv0867c基因并得到了其大肠杆菌表达产物,为进一步研究Rv1884c和Rv0867c基因蛋白的活性及其功能,以及研究结核分枝杆菌快速促生长作用奠定了基础.     

Characterization of P55, a multidrug efflux pump in Mycobacterium bovis and Mycobacterium tuberculosis

The Mycobacterium bovis P55 gene, located downstream from the gene that encodes the immunogenic lipoprotein P27, has been characterized. The gene was identical to the open reading frame of the Rv1410c gene in the genome of Mycobacterium tuberculosis H37Rv, annotated as a probable drug efflux protein. Genes similar to P55 were present in all species of the M. tuberculosis complex and other mycobacteria such as Mycobacterium leprae and Mycobacterium avium. By Western blotting, P55 was located in the membrane fraction of M. bovis. When transformed into Mycobacterium smegmatis after cloning, P55 conferred aminoglycoside and tetracycline resistance. The levels of resistance to streptomycin and tetracycline conferred by P55 were decreased in the presence of the protonophore carbonyl cyanide m-chlorophenylhydrazone and the pump inhibitors verapamil and reserpine. M. smegmatis cells expressing the plasmid-encoded P55 accumulated less tetracycline than the control cells. We conclude that P55 is a membrane protein implicated in aminoglycoside and tetracycline efflux in mycobacteria.     

New plasmid-mediated fluoroquinolone efflux pump, QepA, found in an Escherichia coli clinical isolate

Plasmid-mediated Qnr and AAC(6')-Ib-cr have been recognized as new molecular mechanisms affecting fluoroquinolone (FQ) resistance. C316, an Escherichia coli strain demonstrating resistance to various FQs, was isolated in Japan. Resistance to FQs was augmented in an E. coli CSH2 transconjugant, but PCR failed to detect qnr genes, suggesting the presence of novel plasmid-mediated FQ resistance mechanisms. Susceptibility tests, DNA manipulation, and analyses of the gene and its product were performed to characterize the genetic determinant. A novel FQ-resistant gene, qepA, was identified in a plasmid, pHPA, of E. coli C316, and both qepA and rmtB genes were mediated by a probable transposable element flanked by two copies of IS26. Levels of resistance to norfloxacin, ciprofloxacin, and enrofloxacin were significantly elevated in E. coli transformants harboring qepA under AcrB-TolC-deficient conditions. QepA showed considerable similarities to transporters belonging to the 14-transmembrane-segment family of environmental actinomycetes. The effect of carbonyl cyanide m-chlorophenylhydrazone (CCCP) on accumulation of norfloxacin was assayed in a qepA-harboring E. coli transformant. The intracellular accumulation of norfloxacin was decreased in a qepA-expressing E. coli transformant, but this phenomenon was canceled by CCCP. The augmented FQ resistance level acquired by the probable intergeneric transfer of a gene encoding a major facilitator superfamily-type efflux pump from some environmental microbes to E. coli was first identified. Surveillance of the qepA-harboring clinical isolates should be encouraged to minimize further dissemination of the kind of plasmid-dependent FQ resistance determinants among pathogenic microbes.     

Molecular cloning and characterization of an ABC multidrug efflux pump,VcaM, in Non-O1 Vibrio cholerae

A gene responsible for multidrug resistance was cloned from the chromosomal DNA of non-O1 Vibrio cholerae NCTC 4716 by using as a host drug-hypersensitive Escherichia coli strain KAM32, which lacks major multidrug efflux pumps. E. coli cells transformed with the gene showed elevated levels of resistance to a number of structurally dissimilar drugs, such as tetracycline, norfloxacin, ciprofloxacin, doxorubicin, daunomycin, 4',6-diamidino-2-phenylindole, and Hoechst 33342. We determined the nucleotide sequence and found one open reading frame. We designated the gene vcaM. The deduced product, VcaM, seems to be a polypeptide with 619 amino acid residues (69 kDa) that has a putative topology of six transmembrane segments in the N-terminal hydrophobic domain, followed by an ATP binding domain in the C-terminal hydrophilic region. The sequence of VcaM was shown to be similar to those of human multidrug resistance proteins P-glycoprotein MDR1 and lactococcal LmrA, which are driven by ATP. The efflux of Hoechst 33342 and doxorubicin from cells possessing VcaM was detected. The efflux activity was inhibited by reserpine and sodium o-vanadate, which are potent inhibitors of MDR1 and LmrA. Thus, we conclude that VcaM is a member of the family of multidrug efflux pumps of the ATP binding cassette type and the first experimentally proven example of a multidrug efflux pump of this family in gram-negative bacteria.     

结核分枝杆菌Rv3872基因的克隆、表达和纯化

目的原核表达并纯化结核分枝杆菌Rv3872蛋白。方法聚合酶链反应（PCR）技术从结核分枝杆菌标准株H37Rv全基因组中扩增出的表达Rv3872基因序列，将其克隆到pMD18-T载体后，测序分析。亚克隆该目的基因到pET28a表达载体，最终转化至大肠杆菌BL21（DE3），获得正确的阳性克隆子后大量表达重组Rv3872蛋白，再经纯化、定量后，通过Western blot分析其抗原性。结果扩增Rv3872基因经序列测定与GenBank公布的序列完全一致，表达蛋白经SDS-PAGE分析，在约15000kD处有表达条带，纯化后的重组蛋白占总蛋白的90％以上。免疫印迹分析显示重组的Rv3872蛋白具有抗原性。结论成功表达结核分枝杆菌的Rv3872蛋白，为结核病血清学诊断候选抗原筛选和开发应用打下基础。     

A multidrug efflux pump inhibitor reduces fluoroquinolone resistance in Pseudomonas aeruginosa isolates

In general, resistance to fluoroquinolones (FQs) in gram-negative bacteria is acquired either by mutations in DNA gyrase and topoisomerase IV or by active export of the agents via antibiotic efflux pumps. Reduced porin expression is also proposed to be another mechanism leading to resistance. In this study, interaction between levofloxacin, ofloxacin, and ciprofloxacin with MC-207,110 (multidrug efflux pump inhibitor) was investigated by a checkerboard assay using Pseudomonas aeruginosa. Levofloxacin, ofloxacin, and ciprofloxacin were tested at different concentrations (0.06-64 microg/ml) and MC-207,110 was tested at a concentration range of 4-128 microg/ml. In the presence of MC-207,110 (at 128, 64, 32, 16 microg/ml) resistance to FQs was inhibited significantly and MIC values were decreased, except at 8 and 4 microg/ml of MC-207,110. When MC-207,110 was used, resistance of P. aeruginosa to FQs in vitro was inhibited significantly, suggesting that MC-207,110 may be useful for use in clinical treatment protocols to overcome FQs resistance.     

Use of an efflux pump inhibitor to determine the prevalence of efflux pump-mediated fluoroquinolone resistance and multidrug resistance in Pseudomonas aeruginosa

Fluoroquinolone-resistance in Pseudomonas aeruginosa may be due to efflux pump overexpression (EPO) and/or target mutations. EPO can result in multidrug resistance (MDR) due to broad substrate specificity of the pumps. MC-04,124, an efflux pump inhibitor (EPI) shown to significantly potentiate activity of levofloxacin in P. aeruginosa, was used to examine the prevalence of EPO in clinical isolates. MICs were determined for ciprofloxacin, levofloxacin, moxifloxacin, and gatifloxacin with or without EPI and for other antipseudomonal agents by using broth microdilution against P. aeruginosa isolates from adults (n = 119) and children (n = 24). The prevalence of the EPO phenotype (>/=8-fold MIC decrease when tested with EPI) was compared among subgroups with different resistance profiles. The EPO phenotype was more prevalent among levofloxacin-resistant than levofloxacin-sensitive strains (61%, 48/79 versus 9%, 6/64). EPO was present in 60% of fluoroquinolone-resistant strains without cross-resistance, while it was present at variable frequencies among strains with cross-resistance to other agents: piperacillin-tazobactam (86%), ceftazidime (76%), cefepime (65%), imipenem (56%), gentamicin (55%), tobramycin (48%), and amikacin (27%). The magnitude of MIC decrease with an EPI paralleled the frequency of which the EPO phenotype was observed in different subgroups. EPI reduced the levofloxacin MIC by as much as 16-fold in eight strains for which MICs were 128 microg/ml. Efflux-mediated resistance appears to contribute significantly to fluoroquinolone resistance and MDR in P. aeruginosa. Our data support the fact that increased fluoroquinolone usage can negatively impact susceptibility of P. aeruginosa to multiple classes of antipseudomonal agents.     

三种外排泵抑制剂对氧氟沙星药物抗结核分枝杆菌最低抑菌浓度的影响

目的研究三种外排泵抑制剂对氧氟沙星(OFLX)抗结核分枝杆菌最低抑菌浓度(MIC)的影响。方法在96孔板上应用加入变色剂的7H9培养基进行实验。OFLX经倍比稀释后一系列药物浓度对12株结核分枝杆菌临床分离株的抑菌作用作为对照。经过实验确定羰基氰氯苯腙、维拉帕米和利血平三种常用外排泵抑制剂对OFLX抗结核分枝杆菌MIC的影响。结果三种泵抑制剂对OFLX抗8株OFLX耐药菌MIC呈现了不同程度的影响。在8株耐药菌中利血平对OFLX的MIC值降低了32～64倍,影响均非常明显。8株耐药菌中的6株菌维拉帕米与羰基氰氯苯腙两种泵抑制剂对OFLX的MIC影响程度相同,其中4株菌的MIC值几乎不影响,另外2株菌的MIC值降低了32倍。8株耐药菌中的另2株菌维拉帕米与羰基氰氯苯腙对OFLX的MIC值影响的差异却高达32倍。三种泵抑制剂对4株敏感菌OFLX的MIC影响相对一致,影响总体表现较小。结论三种抑制剂因其机制不同导致其对OFLX抗结核分枝杆菌的影响存在差异。对敏感菌影响相对一致,对耐药菌呈现不同的影响程度。     

Plasmid-mediated fluoroquinolone efflux pump gene, qepA, in Escherichia coli clinical isolates in Korea

The qepA gene was detected in 4 (0.6%) of 621 nonduplicate Escherichia coli clinical isolates collected from blood cultures in Korea. Three of the 4 qepA-positive isolates contained bla_CTX-M-14 and/or bla_TEM-1 genes, but not the E8700 isolate. The qepA gene was successfully transferred and conferred resistance to hydrophilic quinolones, such as norfloxacin and ciprofloxacin, in the recipient. The gene was located in part of IS26. Two isolates were linked to the truncated rmtB gene.     

Mycobacterium tuberculosis Rv3802c Encodes a Phospholipase/Thioesterase and Is Inhibited by the Antimycobacterial Agent Tetrahydrolipstatin

The cell wall of M. tuberculosis is central to its success as a pathogen. Mycolic acids are key components of this cell wall. The genes involved in joining the α and mero mycolates are located in a cluster, beginning with Rv3799c and extending at least until Rv3804c. The role of each enzyme encoded by these five genes is fairly well understood, except for Rv3802c. Rv3802 is one of seven putative cutinases encoded by the genome of M. tuberculosis. In phytopathogens, cutinases hydrolyze the waxy layer of plants, cutin. In a strictly mammalian pathogen, such as M. tuberculosis, it is likely that these proteins perform a different function. Of the seven, we chose to focus on Rv3802c because of its location in a mycolic acid synthesis gene cluster, its putative essentiality, its ubiquitous presence in actinomycetes, and its conservation in the minimal genome of Mycobacterium leprae. We expressed Rv3802 in Escherichia coli and purified the enzymatically active form. We probed its activities and inhibitors characterizing those relevant to its possible role in mycolic acid biosynthesis. In addition to its reported phospholipase A activity, Rv3802 has significant thioesterase activity, and it is inhibited by tetrahydrolipstatin (THL). THL is a described anti-tuberculous compound with an unknown mechanism, but it reportedly targets cell wall synthesis. Taken together, these data circumstantially support a role for Rv3802 in mycolic acid synthesis and, as the cell wall is integral to M. tuberculosis pathogenesis, identification of a novel cell wall enzyme and its inhibition has therapeutic and diagnostic implications.