1 Unité de Pharmacologie Cellulaire et Moléculaire, Université Catholique de Louvain, Brussels; 2 Laboratoire de Microbiologie, Cliniques Universitaires de Mont-Godinne, Université Catholique de Louvain, Yvoir, Belgium; 3 Laboratoire de Bactériologie, Centre Hospitalier Universitaire Jean Minjoz, Besançon, France; 4 Département de Microbiologie, Université de Genève, Geneva, Switzerland
Keywords: antibiotic, efflux, transporters, prokaryotes, resistance
Originally described in bacteria, drug transporters (or efflux pumps) are now recognized as major determinants in the modulation of the accumulation and efflux of antibacterials in virtually all cell types, from prokaroytes to superior eukaryotes. Transport proteins are in fact major cellular products. Based on sequence similarities with known transporters and with proteins possessing at least two transmembrane segments, it has been calculated that 1520% of the genome of Escherichia coli or of Saccharomyces cerevisiae may code for this type of protein.1 At least 300 gene products are proposed to transport known substrates effectively, out of which 2030 transport antibiotics and other drugs.2 Figure 1, on this basis, identifies the main groups of transporters (also referred to as superfamilies) that have been shown so far to act effectively upon antibiotics. Two of these superfamilies [major facilitator superfamily (MFS) and ATP binding cassette superfamily (ABC)] span the prokaryoteeukaryote boundary, but with specific members in each kingdom. It must be remembered, however, that most transporters have been identified only very recently, so that the discovery of many more families, with both prokaryotic and eukaryotic members, would not be surprising in the near future. Efflux pumps usually consist of a monocomponent protein with several transmembrane spanning domains (most often 12 of them). However, in Gram-negative bacteria, which are protected by an outer membrane, efflux transporters can be organized as multicomponent systems, in which the efflux pump located in the inner membrane works in conjunction with a periplasmic fusion protein and an outer membrane protein (Figure 2).3 This first review focuses on the impact for antibiotic treatments of efflux pumps found in prokaryotes, while the companion paper4 examines those characterized in eukaryotes.
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Why antibiotic transporters? |
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What are the main antibiotic transporters? |
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Impact on resistance |
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Secondly, concomitant expression of several efflux pumps in a given bacterial species may lead to apparently high level resistance phenotypes when considering the shared substrates. This has been observed in Gram-negative bacteria, in which the multicomponent efflux pumps of the RND superfamily transport antibiotics from the cytosolic leaflet of the inner membrane to the periplasmic space, and the single component efflux pumps of the MFS superfamily promote efflux from this space to the external medium.25
Thirdly, efflux may also cooperate with other resistance mechanisms to confer not only high level but also broad-spectrum resistance. For example, the high intrinsic penem resistance of P. aeruginosa results from the interplay between the outer membrane barrier, theactive efflux system MexABOprM and AmpC ß-lactamase.26 In E. coli, expression of class-C ß-lactamase confers resistance to first- and second-generation cephalosporins, and expression of pump AcrB causes resistance to most penicillins. The global result is that the organism becomes susceptible only to third- or fourth-generation cephalosporins.20 A more indirect but probably very effective mode of cooperation is exemplified by the combination of DNA gyrase and/or topoisomerase IV mutation and efflux in the development of resistance to fluoroquinolones. Whereas single target mutations confer only a low level of resistance, the reduction in the intrabacterial concentration of fluoroquinolones through expression of one or several efflux pumps may result in MICs exceeding breakpoints (see 27 for a recent example). Thus, resistant strains from clinical sources28 often display a combination of multiple mutations in the target genes and overexpression of efflux transporters.29 More critically, the exposure of the targets to insufficient drug concentrations will favour the selection of mutants. Thus, constitutive expression of efflux pumps acting on fluoroquinolones probably explains the high frequency of mutations leading to resistance in Gram-negative bacteria. This has been particularly well demonstrated for levofloxacin and P. aeruginosa. Disruption of the genes of three RND pumps not only brings the MIC from 0.25 to <0.02 mg/L, but, most strikingly, reduces the frequency of appearance of first-step mutants from 2 x 107 to <1011.19 It must, however, be emphasized that all pumps must be inactivated simultaneously to obtain such an effect, since the lack of activity of one can be easily compensated for by overexpression of others with overlapping spectra.30
Fourthly, antibiotics can serve as inducers and regulate the expression of some efflux pumps at the level of gene transcription or mRNA translation, by interacting with regulator systems.31 Transporters may also become overexpressed as a result of mutations occurring in these regulators3 (this mechanism may be the predominant one for resistance of P. aeruginosa to fluoroquinolones in cystic fibrosis patients).32 More importantly, global regulation may be involved,33 causing the overexpression of several independent genes (regulons).34 For instance, the mar regulon in E. coli may control not only the expression of AcrB, but probably also that of other drug-specific transporters and porins, together with numerous other proteins involved in stress responses (see 35 and the references cited therein). Worryingly, mutations in regulator genes might even result in constitutive expression of several efflux pumps, causing multiple resistance.
Fifthly, resistance by efflux can be easily disseminated. In several cases, the genetic elements encoding efflux pumps and their regulators are located on plasmids (such as Tet transporters in Gram-positive bacteria), or on conjugative or transformable transposons located either on plasmids (Tet transporters also, but in Gram-negative bacteria), or in the chromosome (e.g. mef genes in Streptococcus pneumoniae).36 Importantly, efflux-mediated resistance mechanisms can spread between phylogenically very distant species. This is exemplified by the macrolide-mediated efflux, which has moved not only among streptococci but also to Gram-negative bacteria.37 Co-transfer with genes for other resistance mechanisms may also take place if these are present together on large mobile genetic elements.
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Strategies for the future |
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Moving to the evaluation of new antibiotics, exploring their potential recognition by typical efflux transporters must now be in the forefront of their pre-clinical and clinical assessment. All other pharmacological and toxicological properties being equal, the aim here will be to favour the selection of derivatives that are poor substrates of the efflux pumps and that do not induce their overexpression. Table illustrates the relative affinity of current and newly introduced antibiotics for efflux transporters, and reveals that most recent antibiotics in each class are less well recognized than those that are older. The development of pump inhibitors as adjuvant therapy also represents an interesting area for drug discovery, similar to how ß-lactamase inhibitors brought new life to ß-lactams.43 This approach, however, appears very challenging because of potential effects on efflux transporters also present in eukaryotic cells. It must be emphasized that most inhibitors currently available display strong pharmacological activities in eukaryotic cell systems and are therefore unusable in clinical practice. Typical examples include reserpine,44 omeprazole,45 phenothiazines,46 sertraline,47 verapamil48 and siderophores.49 It is therefore essential to develop molecules not only designed specifically to inhibit prokaryotic transporters, but also with some distance from molecular structures close to those of drugs. Another difficulty is that the pharmacokinetic/dynamic properties of the pump inhibitors will need to match closely those of the companion antibiotic. Only three main categories of compound have been uncovered so far.50 The first group comprises compounds specifically raised against the Tet transporters for tetracyclines (namely tetracycline derivatives substituted in position 13 and probably acting as competitive inhibitors,51 and a non-competitive inhibitor built on an indan nucleus).52 The second group is represented by a family of flavonolignans derived from a natural alkaloid from Onopordon corymbosum.53 These molecules inhibit the NorA transporter of Staphylococcus aureus. As flavones are also known to inhibit the eukaryotic P-glycoprotein, considerable lead optimization studies will be needed to obtain safe compounds. The third category is represented by peptides acting upon the RND transporters of P. aeruginosa.54 These inhibitors selectively improve the activity of antibiotics that are substrates of the MexB efflux pump (quinolones, macrolides, chloramphenicol, and to a lesser extent, tetracycline or carbenicillin),55 which suggests a high level of specificity.56 They do not interact with the eukaryotic P-glycoprotein. A desirable step forward would be to consider the design of wider spectrum inhibitors acting on pumps present in both Gram-positive and Gram-negative bacteria and belonging to different phylogenetic families. Prudent use of these inhibitors will, however, be essential, to avoid fast emergence of resistance to them, which will most probably also emerge. Laboratory mutants of Bacillus subtilis have already been isolated with resistance to the inhibitory activity of reserpine.57
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Acknowledgements |
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Footnotes |
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References |
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2
.
Saier, M. H., Jr (2002). [Online.] http://www-biology.ucsd.edu/msaier/transport/ (19 January 2003, date last accessed).
3
.
Poole, K. (2000). Efflux-mediated resistance to fluoroquinolones in Gram-negative bacteria. Antimicrobial Agents and Chemotherapy 44, 223341.
4 . Van Bambeke, F., Michot, J.-M. & Tulkens, P. M. (2003). Antibiotic efflux pumps in eukaryotic cells: occurrence and impact on antibiotic cellular pharmacokinetics, pharmacodynamics and toxicodynamics. Journal of Antimicrobial Chemotherapy 51, 106777.
5 . McMurry, L., Petrucci, R. E., Jr & Levy, S. B. (1980). Active efflux of tetracycline encoded by four genetically different tetracycline resistance determinants in Escherichia coli. Proceedings of the National Academy of Sciences, USA 77, 39747.[Abstract]
6 . Ross, J. I., Eady, E. A., Cove, J. H., Cunliffe, W. J., Baumberg, S. & Wootton, J. C. (1990). Inducible erythromycin resistance in staphylococci is encoded by a member of the ATP-binding transport super-gene family. Molecular Microbiology 4, 120714.[ISI][Medline]
7 . Yoshida, H., Bogaki, M., Nakamura, S., Ubukata, K. & Konno, M. (1990). Nucleotide sequence and characterization of the Staphylococcus aureus norA gene, which confers resistance to quinolones. Journal of Bacteriology 172, 69429.[ISI][Medline]
8 . Li, X. Z., Ma, D., Livermore, D. M. & Nikaido, H. (1994). Role of efflux pump(s) in intrinsic resistance of Pseudomonas aeruginosa: active efflux as a contributing factor to beta-lactam resistance. Antimicrobial Agents and Chemotherapy 38, 174252.[Abstract]
9
.
Aires, J. R., Kohler, T., Nikaido, H. & Plesiat, P. (1999). Involvement of an active efflux system in the natural resistance of Pseudomonas aeruginosa to aminoglycosides. Antimicrobial Agents and Chemotherapy 43, 26248.
10 . Poole, K. (2002). Mechanisms of bacterial biocide and antibiotic resistance. Journal of Applied Microbiology 92, Suppl., 55S64S.[CrossRef][ISI][Medline]
11 . Thanassi, D. G., Cheng, L. W. & Nikaido, H. (1997). Active efflux of bile salts by Escherichia coli. Journal of Bacteriology 179, 25128.[Abstract]
12
.
Hirakata, Y., Srikumar, R., Poole, K., Gotoh, N., Suematsu, T., Kohno, S. et al. (2002). Multidrug efflux systems play an important role in the invasiveness of Pseudomonas aeruginosa. Journal of Experimental Medicine 196, 10918.
13 . Rahmati, S., Yang, S., Davidson, A. L. & Zechiedrich, E. L. (2002). Control of the AcrAB multidrug efflux pump by quorum-sensing regulator SdiA. Molecular Microbiology 43, 67785.[CrossRef][ISI][Medline]
14
.
Sanchez, P., Linares, J. F., Ruiz-Diez, B., Campanario, E., Navas, A., Baquero, F. et al. (2002). Fitness of in vitro selected Pseudomonas aeruginosa nalB and nfxB multidrug resistant mutants. Journal of Antimicrobial Chemotherapy 50, 65764.
15
.
Kohler, T., van Delden, C., Curty, L. K., Hamzehpour, M. M. & Pechere, J. C. (2001). Overexpression of the MexEF-OprN multidrug efflux system affects cell-to-cell signaling in Pseudomonas aeruginosa. Journal of Bacteriology 183, 521322.
16
.
Sharff, A., Fanutti, C., Shi, J., Calladine, C. & Luisi, B. (2001). The role of the TolC family in protein transport and multidrug efflux. From stereochemical certainty to mechanistic hypothesis. European Journal of Biochemistry 268, 501126.
17 . Cundliffe, E. (1992). Self-protection mechanisms in antibiotic producers. Ciba Foundation Symposium 171, 199208.[ISI][Medline]
18
.
Piddock, L. J., Jin, Y. F., Webber, M. A. & Everett, M. J. (2002). Novel ciprofloxacin-resistant, nalidixic acid-susceptible mutant of Staphylococcus aureus. Antimicrobial Agents and Chemotherapy 46, 22768.
19
.
Lomovskaya, O., Lee, A., Hoshino, K., Ishida, H., Mistry, A., Warren, M. S. et al. (1999). Use of a genetic approach to evaluate the consequences of inhibition of efflux pumps in Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 43, 13406.
20
.
Mazzariol, A., Cornaglia, G. & Nikaido, H. (2000). Contributions of the AmpC beta-lactamase and the AcrAB multidrug efflux system in intrinsic resistance of Escherichia coli K-12 to beta-lactams. Antimicrobial Agents and Chemotherapy 44, 138790.
21 . Lynch, J. P., III & Martinez, F. J. (2002). Clinical relevance of macrolide-resistant Streptococcus pneumoniae for community-acquired pneumonia. Clinical Infectious Diseases 34, Suppl. 1, S2746.[CrossRef][ISI][Medline]
22 . Li, X. Z., Nikaido, H. & Poole, K. (1995). Role of mexA-mexB-oprM in antibiotic efflux in Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 39, 194853.[Abstract]
23 . Mata, M. T., Baquero, F. & Perez-Diaz, J. C. (2000). A multidrug efflux transporter in Listeria monocytogenes. FEMS Microbiology Letters 187, 1858.[CrossRef][ISI][Medline]
24 . Bozdogan, B., Peric, M., Jacobs, M. R. & Appelbaum, P. C. (2002). Macrolide hyper-susceptibility is associated with the absence of efflux mechanism in clinical isolates of H. influenzae. In Program and Abstracts of the Forty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, CA, USA, 2002. Abstract C1-1612, p. 76. American Society for Microbiology, Washington, DC, USA.
25 . Lomovskaya, O. (2002). Interactions among multiple efflux pumps: additive and synergistic effects on antimicrobial resistance. In Program and Abstracts of the Forty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, CA, USA, 2002. Abstract 1188, p. 466. American Society for Microbiology, Washington, DC, USA.
26
.
Okamoto, K., Gotoh, N. & Nishino, T. (2001). Pseudomonas aeruginosa reveals high intrinsic resistance to penem antibiotics: penem resistance mechanisms and their interplay. Antimicrobial Agents and Chemotherapy 45, 196471.
27
.
Le Thomas, I., Couetdic, G., Clermont, O., Brahimi, N., Plesiat, P. & Bingen, E. (2001). In vivo selection of a target/efflux double mutant of Pseudomonas aeruginosa by ciprofloxacin therapy. Journal of Antimicrobial Chemotherapy 48, 5535.
28 . Yoshida, T., Muratani, T., Iyobe, S. & Mitsuhashi, S. (1994). Mechanisms of high-level resistance to quinolones in urinary tract isolates of Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 38, 14669.[Abstract]
29 . Jalal, S. & Wretlind, B. (1998). Mechanisms of quinolone resistance in clinical strains of Pseudomonas aeruginosa. Microbial Drug Resistance 4, 25761.[ISI][Medline]
30
.
Li, X. Z., Barre, N. & Poole, K. (2000). Influence of the MexA-MexB-OprM multidrug efflux system on expression of the MexC-MexD-OprJ and MexE-MexF-OprN multidrug efflux systems in Pseudomonas aeruginosa. Journal of Antimicrobial Chemotherapy 46, 88593.
31 . Roberts, M. C. (1996). Tetracycline resistance determinants: mechanisms of action, regulation of expression, genetic mobility, and distribution. FEMS Microbiology Reviews 19, 124.[CrossRef][ISI][Medline]
32
.
Jalal, S., Ciofu, O., Hoiby, N., Gotoh, N. & Wretlind, B. (2000). Molecular mechanisms of fluoroquinolone resistance in Pseudomonas aeruginosa isolates from cystic fibrosis patients. Antimicrobial Agents and Chemotherapy 44, 7102.
33
.
Pumbwe, L. & Piddock, L. J. (2000). Two efflux systems expressed simultaneously in multidrug-resistant Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 44, 28614.
34 . George, A. M. (1996). Multidrug resistance in enteric and other Gram-negative bacteria. FEMS Microbiology Letters 139, 110.[CrossRef][ISI][Medline]
35
.
Barbosa, T. M. & Levy, S. B. (2000). Differential expression of over 60 chromosomal genes in Escherichia coli by constitutive expression of MarA. Journal of Bacteriology 182, 346774.
36
.
Del Grosso, M., Iannelli, F., Messina, C., Santagati, M., Petrosillo, N., Stefani, S. et al. (2002). Macrolide efflux genes mef(A) and mef(E) are carried by different genetic elements in Streptococcus pneumoniae. Journal of Clinical Microbiology 40, 7748.
37
.
Luna, V. A., Cousin, S., Jr, Whittington, W. L. & Roberts, M. C. (2000). Identification of the conjugative mef gene in clinical Acinetobacter junii and Neisseria gonorrhoeae isolates. Antimicrobial Agents and Chemotherapy 44, 25036.
38
.
Farrell, D. J., Morrissey, I., Bakker, S. & Felmingham, D. (2002). Molecular characterization of macrolide resistance mechanisms among Streptococcus pneumoniae and Streptococcus pyogenes isolated from the PROTEKT 19992000 study. Journal of Antimicrobial Chemotherapy 50, Suppl. S1, 3947.
39
.
Ziha-Zarifi, I., Llanes, C., Kohler, T., Pechere, J. C. & Plesiat, P. (1999). In vivo emergence of multidrug-resistant mutants of Pseudomonas aeruginosa overexpressing the active efflux system MexA-MexB-OprM. Antimicrobial Agents and Chemotherapy 43, 28791.
40 . Sutcliffe, J., Grebe, T., Tait-Kamradt, A. & Wondrack, L. (1996). Detection of erythromycin-resistant determinants by PCR. Antimicrobial Agents and Chemotherapy 40, 25626.[Abstract]
41
.
Aminov, R. I., Chee-Sanford, J. C., Garrigues, N., Teferedegne, B., Krapac, I. J., White, B. A. et al. (2002). Development, validation, and application of PCR primers for detection of tetracycline efflux genes of Gram-negative bacteria. Applied and Environmental Microbiology 68, 178693.
42 . Prudencio, C., Sansonetty, F., Sousa, M. J., Corte-Real, M. & Leao, C. (2000). Rapid detection of efflux pumps and their relation with drug resistance in yeast cells. Cytometry 39, 2635.[CrossRef][ISI][Medline]
43 . Ryan, B. M., Dougherty, T. J., Beaulieu, D., Chuang, J., Dougherty, B. A. & Barrett, J. F. (2001). Efflux in bacteria: what do we really know about it? Expert Opinion on Investigational Drugs 10, 140922.[ISI][Medline]
44
.
Brenwald, N. P., Gill, M. J. & Wise, R. (1997). The effect of reserpine, an inhibitor of multi-drug efflux pumps, on the in-vitro susceptibilities of fluoroquinolone-resistant strains of Streptococcus pneumoniae to norfloxacin. Journal of Antimicrobial Chemotherapy 40, 45860.
45
.
Aeschlimann, J. R., Dresser, L. D., Kaatz, G. W. & Rybak, M. J. (1999). Effects of NorA inhibitors on in vitro antibacterial activities and postantibiotic effects of levofloxacin, ciprofloxacin, and norfloxacin in genetically related strains of Staphylococcus aureus. Antimicrobial Agents and Chemotherapy 43, 33540.
46 . Molnar, J., Hever, A., Fakla, I., Fischer, J., Ocsovski, I. & Aszalos, A. (1997). Inhibition of the transport function of membrane proteins by some substituted phenothiazines in E. coli and multidrug resistant tumor cells. Anticancer Research 17, 4816.[ISI][Medline]
47 . Munoz-Bellido, J. L., Munoz-Criado, S. & Garcia-Rodriguez, J. A. (2000). Antimicrobial activity of psychotropic drugs: selective serotonin reuptake inhibitors. International Journal of Antimicrobial Agents 14, 17780.[CrossRef][ISI][Medline]
48 . Cohn, R. C., Rudzienski, L. & Putnam, R. W. (1995). Verapamil-tobramycin synergy in Pseudomonas cepacia but not Pseudomonas aeruginosa in vitro. Chemotherapy 41, 3303.[ISI][Medline]
49 . Rothstein, D. M., McGlynn, M., Bernan, V., McGahren, J., Zaccardi, J., Cekleniak, N. et al. (1993). Detection of tetracyclines and efflux pump inhibitors. Antimicrobial Agents and Chemotherapy 37, 16249.[Abstract]
50 . Lomovskaya, O. & Watkins, W. J. (2001). Efflux pumps: their role in antibacterial drug discovery. Current Medicinal Chemistry 8, 1699711.[ISI][Medline]
51
.
Nelson, M. L. & Levy, S. B. (1999). Reversal of tetracycline resistance mediated by different bacterial tetracycline resistance determinants by an inhibitor of the Tet(B) antiport protein. Antimicrobial Agents and Chemotherapy 43, 171924.
52 . Hirata, T., Wakatabe, R., Nielsen, J., Satoh, T., Nihira, S. & Yamaguchi, A. (1998). Screening of an inhibitor of the tetracycline efflux pump in a tetracycline-resistant clinical isolate of Staphylococcus aureus 743. Biological and Pharmaceutical Bulletin 21, 67881.[Medline]
53 . Guz, N. R., Stermitz, F. R., Johnson, J. B., Beeson, T. D., Willen, S., Hsiang, J. et al. (2001). Flavonolignan and flavone inhibitors of a Staphylococcus aureus multidrug resistance pump: structureactivity relationships. Journal of Medicinal Chemistry 44, 2618.[CrossRef][ISI][Medline]
54 . Renau, T. E., Leger, R., Flamme, E. M., Sangalang, J., She, M. W., Yen, R. et al. (1999). Inhibitors of efflux pumps in Pseudomonas aeruginosa potentiate the activity of the fluoroquinolone antibacterial levofloxacin. Journal of Medicinal Chemistry 42, 492831.[CrossRef][ISI][Medline]
55
.
Lomovskaya, O., Warren, M. S., Lee, A., Galazzo, J., Fronko, R., Lee M. et al. (2001). Identification and characterization of inhibitors of multidrug resistance efflux pumps in Pseudomonas aeruginosa: novel agents for combination therapy. Antimicrobial Agents and Chemotherapy 45, 10516.
56 . Barrett, J. F. (2001). MC-207110 Daiichi Seiyaku/Microcide Pharmaceuticals. Current Opinion on Investigational Drugs 2, 2125.
57
.
Ahmed, M., Borsch, C. M., Neyfakh, A. A. & Schuldiner, S. (1993). Mutants of the Bacillus subtilis multidrug transporter Bmr with altered sensitivity to the antihypertensive alkaloid reserpine. Journal of Biological Chemistry 268, 110869.
58 . Neyfakh, A. A., Borsch, C. M. & Kaatz, G. W. (1993). Fluoroquinolone resistance protein NorA of Staphylococcus aureus is a multidrug efflux transporter. Antimicrobial Agents and Chemotherapy 37, 1289.[Abstract]
59 . Noguchi, N., Aoki, T., Sasatsu, M., Kono, M., Shishido, K. & Ando, T. (1986). Determination of the complete nucleotide sequence of pNS1, a staphylococcal tetracycline-resistance plasmid propagated in Bacillus subtilis. FEMS Microbiology Letters 37, 2838.[CrossRef][ISI]
60 . Huang, J., OToole P. W., Shen, W., Jiang, X., Lobo, N., Palmer, L. M. et al. (2002). Identification of a novel multidrug resistance efflux system (MdeA) from Staphylococcus aureus. In Program and Abstracts of the Forty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, CA, USA, 2002. Abstract C1-427, p. 65. American Society for Microbiology, Washington, DC, USA.
61 . Tait-Kamradt, A., Clancy, J., Cronan, M., Dib-Hajj, F., Wondrack, L., Yuan, W. et al. (1997). mefE is necessary for the erythromycin-resistant M phenotype in Streptococcus pneumoniae. Antimicrobial Agents and Chemotherapy 41, 22515.[Abstract]
62
.
Gill, M. J., Brenwald, N. P. & Wise, R. (1999). Identification of an efflux pump gene, pmrA, associated with fluoroquinolone resistance in Streptococcus pneumoniae. Antimicrobial Agents and Chemotherapy 43, 1879.
63 . Clancy, J., Petitpas, J., Dib-Hajj, F., Yuan, W., Cronan, M., Kamath, A. V. et al. (1996). Molecular cloning and functional analysis of a novel macrolide-resistance determinant, mefA, from Streptococcus pyogenes. Molecular Microbiology 22, 86779.[CrossRef][ISI][Medline]
64 . Godreuil, S., Galimand, M., Gerbaud, G. & Courvalin, P. (2001). Efflux pump Lde is associated with fluoroquinolone resistance in Listeria monocytogenes CLIP 21369. In Program and Abstracts of the Forty-first Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, IL, USA, 2001. Abstract UL-11. American Society for Microbiology, Washington, DC, USA.
65
.
De Rossi, E., Branzoni, M., Cantoni, R., Milano, A., Riccardi, G. & Ciferri, O. (1998). mmr, a Mycobacterium tuberculosis gene conferring resistance to small cationic dyes and inhibitors. Journal of Bacteriology 180, 606871.
66 . Chaudhuri, B. S., Bhakta, S., Barik, R., Basu, J., Kundu, M. & Chakrabarti, P. (2002). Overexpression and functional characterization of an ABC transporter encoded by the genes drrA and drrB of Mycobacterium tuberculosis. Biochemical Journal 367, 27985.[CrossRef][ISI][Medline]
67
.
Luna, V. A., Coates, P., Eady, E. A., Cove, J. H., Nguyen, T. T. & Roberts, M. C. (1999). A variety of Gram-positive bacteria carry mobile mef genes. Journal of Antimicrobial Chemotherapy 44, 1925.
68
.
Jonas, B. M., Murray, B. E. & Weinstock, G. M. (2001). Characterization of emeA, a norA homolog and multidrug resistance efflux pump, in Enterococcus faecalis. Antimicrobial Agents and Chemotherapy 45, 35749.
69
.
Singh, K. V., Weinstock, G. M. & Murray, B. E. (2002). An Enterococcus faecalis ABC homologue (Lsa) is required for the resistance of this species to clindamycin and quinupristin-dalfopristin. Antimicrobial Agents and Chemotherapy 46, 184550.
70 . Sanchez, L., Pan, W., Vinas, M. & Nikaido, H. (1997). The acrAB homolog of Haemophilus influenzae codes for a functional multidrug efflux pump. Journal of Bacteriology 179, 68557.[Abstract]
71 . Hagman, K. E., Lucas, C. E., Balthazar, J. T., Snyder, L., Nilles, M., Judd, R. C. et al. (1997). The MtrD protein of Neisseria gonorrhoeae is a member of the resistance/nodulation/division protein family constituting part of an efflux system. Microbiology 143, 211725.[Abstract]
72 . Nikaido, H. (1998). Antibiotic resistance caused by Gram-negative multidrug efflux pumps. Clinical Infectious Diseases 27, Suppl. 1, S3241.[ISI][Medline]
73 . Lacroix, F. J., Cloeckaert, A., Grepinet, O., Pinault, C., Popoff, M. Y., Waxin, H. et al. (1996). Salmonella typhimurium acrB-like gene: identification and role in resistance to biliary salts and detergents and in murine infection. FEMS Microbiology Letters 135, 1617.[CrossRef][ISI][Medline]
74
.
Nikaido, H., Basina, M., Nguyen, V. & Rosenberg, E. Y. (1998). Multidrug efflux pump AcrAB of Salmonella typhimurium excretes only those beta-lactam antibiotics containing lipophilic side chains. Journal of Bacteriology 180, 468692.
75 . Arcangioli, M. A., Leroy-Setrin, S., Martel, J. L. & Chaslus-Dancla, E. (1999). A new chloramphenicol and florfenicol resistance gene flanked by two integron structures in Salmonella typhimurium DT104. FEMS Microbiology Letters 174, 32732.[CrossRef][ISI][Medline]
76 . Morimyo, M., Hongo, E., Hama-Inaba, H. & Machida, I. (1992). Cloning and characterization of the mvrC gene of Escherichia coli K-12 which confers resistance against methyl viologen toxicity. Nucleic Acids Research 20, 315965.[Abstract]
77
.
Yerushalmi, H., Lebendiker, M. & Schuldiner, S. (1995). EmrE, an Escherichia coli 12-kDa multidrug transporter, exchanges toxic cations and H+ and is soluble in organic solvents. Journal of Biological Chemistry 270, 685663.
78
.
Morita, Y., Kodama, K., Shiota, S., Mine, T., Kataoka, A., Mizushima, T. et al. (1998). NorM, a putative multidrug efflux protein, of Vibrio parahaemolyticus and its homolog in Escherichia coli. Antimicrobial Agents and Chemotherapy 42, 177882.
79
.
Nishino, K. & Yamaguchi, A. (2001). Analysis of a complete library of putative drug transporter genes in Escherichia coli. Journal of Bacteriology 183, 580312.
80 . Waters, S. H., Rogowsky, P., Grinsted, J., Altenbuchner, J. & Schmitt, R. (1983). The tetracycline resistance determinants of RP1 and Tn1721: nucleotide sequence analysis. Nucleic Acids Research 11, 6089105.[Abstract]
81 . Bentley, J., Hyatt, L. S., Ainley, K., Parish, J. H., Herbert, R. B. & White, G. R. (1993). Cloning and sequence analysis of an Escherichia coli gene conferring bicyclomycin resistance. Gene 127, 11720.[CrossRef][ISI][Medline]
82
.
Vedantam, G., Guay, G. G., Austria, N. E., Doktor, S. Z. & Nichols, B. P. (1998). Characterization of mutations contributing to sulfathiazole resistance in Escherichia coli. Antimicrobial Agents and Chemotherapy 42, 8893.
83 . Edgar, R. & Bibi, E. (1997). MdfA, an Escherichia coli multidrug resistance protein with an extraordinarily broad spectrum of drug recognition. Journal of Bacteriology 179, 227480.[Abstract]
84
.
Blattner, F. R., Plunkett, G., III, Bloch, C. A., Perna, N. T., Burland, V., Riley, M. et al. (1997). The complete genome sequence of Escherichia coli K-12. Science 277, 145374.
85 . Lomovskaya, O. & Lewis, K. (1992). Emr, an Escherichia coli locus for multidrug resistance. Proceedings of the National Academy of Sciences, USA 89, 893842.[Abstract]
86 . Yura, T., Mori, H., Nagai, H., Nagata, T., Ishihama, A., Fujita, N. et al. (1992). Systematic sequencing of the Escherichia coli genome: analysis of the 02.4 min region. Nucleic Acids Research 20, 33058.[Abstract]
87 . Saier, M. H., Jr (2000). Families of transmembrane sugar transport proteins. Molecular Microbiology 35, 699710.[CrossRef][ISI][Medline]
88 . Fujisaki, S., Ohnuma, S., Horiuchi, T., Takahashi, I., Tsukui, S., Nishimura, Y. et al. (1996). Cloning of a gene from Escherichia coli that confers resistance to fosmidomycin as a consequence of amplification. Gene 175, 837.[CrossRef][ISI][Medline]
89 . Ma, D., Cook, D. N., Alberti, M., Pon, N. G., Nikaido, H. & Hearst, J. E. (1993). Molecular cloning and characterization of acrA and acrE genes of Escherichia coli. Journal of Bacteriology 175, 6299313.[Abstract]
90 . Okusu, H., Ma, D. & Nikaido, H. (1996). AcrAB efflux pump plays a major role in the antibiotic resistance phenotype of Escherichia coli multiple-antibiotic-resistance (Mar) mutants. Journal of Bacteriology 178, 3068.[Abstract]
91 . Buysse, J. M., Demyan, W. F., Dunyak, D. S., Stapert, D., Hamel, J. C. & Ford, C. W. (1996). Mutation of the AcrAB antibiotic efflux pump in Escherichia coli confers susceptibility to oxazolidinone antibiotics. In Program and Abstracts of the Thirty-sixth Interscience Conference on Antimicrobial Agents and Chemotherapy, New Orleans, LA, USA, 1996. Abstract C-42. American Society for Microbiology, Washington, DC, USA.
92
.
Rosenberg, E. Y., Ma, D. & Nikaido, H. (2000). AcrD of Escherichia coli is an aminoglycoside efflux pump. Journal of Bacteriology 182, 17546.
93
.
Kobayashi, N., Nishino, K. & Yamaguchi, A. (2001). Novel macrolide-specific ABC-type efflux transporter in Escherichia coli. Journal of Bacteriology 183, 563944.
94
.
Alonso, A. & Martinez, J. L. (2000). Cloning and characterization of SmeDEF, a novel multidrug efflux pump from Stenotrophomonas maltophilia. Antimicrobial Agents and Chemotherapy 44, 307986.
95
.
Zhang, L., Li, X. Z. & Poole, K. (2001). SmeDEF multidrug efflux pump contributes to intrinsic multidrug resistance in Stenotrophomonas maltophilia. Antimicrobial Agents and Chemotherapy 45, 3497503.
96 . Bissonnette, L., Champetier, S., Buisson, J. P. & Roy, P. H. (1991). Characterization of the nonenzymatic chloramphenicol resistance (cmlA) gene of the In4 integron of Tn1696: similarity of the product to transmembrane transport proteins. Journal of Bacteriology 173, 4493502.[ISI][Medline]
97 . Poole, K., Heinrichs, D. E. & Neshat, S. (1993). Cloning and sequence analysis of an EnvCD homologue in Pseudomonas aeruginosa: regulation by iron and possible involvement in the secretion of the siderophore pyoverdine. Molecular Microbiology 10, 52944.[ISI][Medline]
98
.
Kohler, T., Michea-Hamzehpour, M., Epp, S. F. & Pechere, J. C. (1999). Carbapenem activities against Pseudomonas aeruginosa: respective contributions of OprD and efflux systems. Antimicrobial Agents and Chemotherapy 43, 4247.
99
.
Masuda, N., Gotoh, N., Ishii, C., Sakagawa, E., Ohya, S. & Nishino, T. (1999). Interplay between chromosomal beta-lactamase and the MexAB-OprM efflux system in intrinsic resistance to beta-lactams in Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 43, 4002.
100
.
Li, X. Z., Zhang, L., Srikumar, R. & Poole, K. (1998). Beta-lactamase inhibitors are substrates for the multidrug efflux pumps of Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 42, 399403.
101
.
Masuda, N., Sakagawa, E., Ohya, S., Gotoh, N., Tsujimoto, H. & Nishino, T. (2000). Substrate specificities of MexAB-OprM, MexCD-OprJ, and MexXY-oprM efflux pumps in Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 44, 33227.
102 . Poole, K., Gotoh, N., Tsujimoto, H., Zhao, Q., Wada, A., Yamasaki, T. et al. (1996). Overexpression of the mexC-mexD-oprJ efflux operon in nfxB-type multidrug-resistant strains of Pseudomonas aeruginosa. Molecular Microbiology 21, 71324.[ISI][Medline]
103 . Kohler, T., Michea-Hamzehpour, M., Henze, U., Gotoh, N., Curty, L. K. & Pechere, J. C. (1997). Characterization of MexE-MexF-OprN, a positively regulated multidrug efflux system of Pseudomonas aeruginosa. Molecular Microbiology 23, 34554.[ISI][Medline]
104
.
Maseda, H., Yoneyama, H. & Nakae, T. (2000). Assignment of the substrate-selective subunits of the MexEF-OprN multidrug efflux pump of Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 44, 65864.
105
.
Chuanchuen, R., Narasaki, C. T. & Schweizer, H. P. (2002). The MexJK efflux pump of Pseudomonas aeruginosa requires OprM for antibiotic efflux but not for efflux of triclosan. Journal of Bacteriology 184, 503644.
106
.
Mine, T., Morita, Y., Kataoka, A., Mizushima, T. & Tsuchiya, T. (1999). Expression in Escherichia coli of a new multidrug efflux pump, MexXY, from Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 43, 4157.
107 . Clancy, J., Dib-Hajj, F., Petitpas, J. W. & Yuan, W. (1997). Cloning and characterization of a novel macrolide efflux gene, mreA, from Streptococcus agalactiae. Antimicrobial Agents and Chemotherapy 41, 271923.[Abstract]
108
.
Capobianco, J. O., Cao, Z., Shortridge, V. D., Ma, Z., Flamm, R. K. & Zhong, P. (2000). Studies of the novel ketolide ABT-773: transport, binding to ribosomes, and inhibition of protein synthesis in Streptococcus pneumoniae. Antimicrobial Agents and Chemotherapy 44, 15627.
109
.
Giovanetti, E., Montanari, M. P., Marchetti, F. & Varaldo, P. E. (2000). In vitro activity of ketolides telithromycin and HMR 3004 against Italian isolates of Streptococcus pyogenes and Streptococcus pneumoniae with different erythromycin susceptibility. Journal of Antimicrobial Chemotherapy 46, 9058.
110 . Someya, Y., Yamaguchi, A. & Sawai, T. (1995). A novel glycylcycline, 9-(N,N-dimethylglycylamido)-6-demethyl-6-deoxytetracycline, is neither transported nor recognized by the transposon Tn10-encoded metal-tetracycline/H+ antiporter. Antimicrobial Agents and Chemotherapy 39, 2479.[Abstract]
111 . Mendez, B., Tachibana, C. & Levy, S. B. (1980). Heterogeneity of tetracycline resistance determinants. Plasmid 3, 99108.[ISI][Medline]
112
.
Piddock, L. J., Johnson, M., Ricci, V. & Hill, S. L. (1998). Activities of new fluoroquinolones against fluoroquinolone-resistant pathogens of the lower respiratory tract. Antimicrobial Agents and Chemotherapy 42, 295660.
113
.
Heaton, V. J., Goldsmith, C. E., Ambler, J. E. & Fisher, L. M. (1999). Activity of gemifloxacin against penicillin- and ciprofloxacin-resistant Streptococcus pneumoniae displaying topoisomerase- and efflux-mediated resistance mechanisms. Antimicrobial Agents and Chemotherapy 43, 29983000.
114 . Takenouchi, T., Tabata, F., Iwata, Y. , Hanzawa, H., Sugawara, M. & Ohya, S. (1996). Hydrophilicity of quinolones is not an exclusive factor for decreased activity in efflux-mediated resistant mutants of Staphylococcus aureus. Antimicrobial Agents and Chemotherapy 40, 183542.[Abstract]
115
.
Schmitz, F. J., Boos, M., Mayer, S., Kohrer, K., Scheuring, S. & Fluit, A. C. (2002). In vitro activities of novel des-fluoro(6) quinolone BMS-284756 against mutants of Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus selected with different quinolones. Antimicrobial Agents and Chemotherapy 46, 9345.
116 . Dean, C. R., Visalli, M. A., Projan, S. J., Sum, P. E. & Bradford, P. A. (2002). Efflux mediated resistance to tigecycline in Pseudomonas aeruginosa. In Program and Abstracts of the Forty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, CA, USA, 2002. Abstract C1-1601, p. 73. American Society for Microbiology, Washington, DC, USA.
117 . Hirata, T., Nishino, K., Saito, A., Tamura, N. & Yamaguchi, A. (2002). Characterization of a novel tetracycline derivative, tigecycline (GAR-936) as a substrate for efflux proteins: potential for developing resistance in E. coli strains. In Program and Abstracts of the Forty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, CA, USA, 2002. Abstract C1-1602, p. 74. American Society for Microbiology, Washington, DC, USA.
118 . Kaatz, G. W., Moudgal, V. V. & Seo, S. M. (2002). Multidrug efflux phenotype in Straphylococcus aureus conferred by a pump recognizing organic cations and C8-methoxy fluoroquinolones. In Program and Abstracts of the Forty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, CA, USA, 2002. Abstract C1-425, p. 64. American Society for Microbiology, Washington, DC, USA.