Skip to main content
  • ASM
    • Antimicrobial Agents and Chemotherapy
    • Applied and Environmental Microbiology
    • Clinical Microbiology Reviews
    • Clinical and Vaccine Immunology
    • EcoSal Plus
    • Eukaryotic Cell
    • Infection and Immunity
    • Journal of Bacteriology
    • Journal of Clinical Microbiology
    • Journal of Microbiology & Biology Education
    • Journal of Virology
    • mBio
    • Microbiology and Molecular Biology Reviews
    • Microbiology Resource Announcements
    • Microbiology Spectrum
    • Molecular and Cellular Biology
    • mSphere
    • mSystems
  • Log in
  • My alerts
  • My Cart

Main menu

  • Home
  • Articles
    • Current Issue
    • Accepted Manuscripts
    • COVID-19 Special Collection
    • Archive
    • Minireviews
  • For Authors
    • Submit a Manuscript
    • Scope
    • Editorial Policy
    • Submission, Review, & Publication Processes
    • Organization and Format
    • Errata, Author Corrections, Retractions
    • Illustrations and Tables
    • Nomenclature
    • Abbreviations and Conventions
    • Publication Fees
    • Ethics Resources and Policies
  • About the Journal
    • About AAC
    • Editor in Chief
    • Editorial Board
    • For Reviewers
    • For the Media
    • For Librarians
    • For Advertisers
    • Alerts
    • AAC Podcast
    • RSS
    • FAQ
  • Subscribe
    • Members
    • Institutions
  • ASM
    • Antimicrobial Agents and Chemotherapy
    • Applied and Environmental Microbiology
    • Clinical Microbiology Reviews
    • Clinical and Vaccine Immunology
    • EcoSal Plus
    • Eukaryotic Cell
    • Infection and Immunity
    • Journal of Bacteriology
    • Journal of Clinical Microbiology
    • Journal of Microbiology & Biology Education
    • Journal of Virology
    • mBio
    • Microbiology and Molecular Biology Reviews
    • Microbiology Resource Announcements
    • Microbiology Spectrum
    • Molecular and Cellular Biology
    • mSphere
    • mSystems

User menu

  • Log in
  • My alerts
  • My Cart

Search

  • Advanced search
Antimicrobial Agents and Chemotherapy
publisher-logosite-logo

Advanced Search

  • Home
  • Articles
    • Current Issue
    • Accepted Manuscripts
    • COVID-19 Special Collection
    • Archive
    • Minireviews
  • For Authors
    • Submit a Manuscript
    • Scope
    • Editorial Policy
    • Submission, Review, & Publication Processes
    • Organization and Format
    • Errata, Author Corrections, Retractions
    • Illustrations and Tables
    • Nomenclature
    • Abbreviations and Conventions
    • Publication Fees
    • Ethics Resources and Policies
  • About the Journal
    • About AAC
    • Editor in Chief
    • Editorial Board
    • For Reviewers
    • For the Media
    • For Librarians
    • For Advertisers
    • Alerts
    • AAC Podcast
    • RSS
    • FAQ
  • Subscribe
    • Members
    • Institutions
Mechanisms of Resistance

In Vivo Increase in Resistance to Ciprofloxacin inEscherichia coli Associated with Deletion of the C-Terminal Part of MarR

Hans-Jörg Linde, Frank Notka, Michaela Metz, Bernd Kochanowski, Peter Heisig, Norbert Lehn
Hans-Jörg Linde
Institute for Medical Microbiology and Hygiene, University of Regensburg, Regensburg,and
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Frank Notka
Institute for Medical Microbiology and Hygiene, University of Regensburg, Regensburg,and
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Michaela Metz
Institute for Medical Microbiology and Hygiene, University of Regensburg, Regensburg,and
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Bernd Kochanowski
Institute for Medical Microbiology and Hygiene, University of Regensburg, Regensburg,and
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Peter Heisig
Pharmazeutische Mikrobiologie, Universität Bonn, Bonn, Germany
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Norbert Lehn
Institute for Medical Microbiology and Hygiene, University of Regensburg, Regensburg,and
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
DOI: 10.1128/AAC.44.7.1865-1868.2000
  • Article
  • Figures & Data
  • Info & Metrics
  • PDF
Loading

ABSTRACT

We recovered two isolates (EP1 and EP2) of Escherichia coli from the same patient that had identical pulsed-field gel electrophoresis patterns but required different MICs of ciprofloxacin (CIP): 16 and 256 mg/liter for EP1 and EP2, respectively. Both isolates had mutations in the quinolone resistance-determining regions of GyrA (Ser83Leu and Asp87Tyr) and ParC (Ser80Ile), but not in those regions of GyrB or ParE. Isolate EP2 was also more resistant to chloramphenicol, tetracyclines, cefuroxime, and organic solvents. A deletion of adenine (A) 1821 was found in marR of isolate EP2, which resulted in an 18-amino-acid C-terminal deletion in the MarR protein. The causative relationship between ΔA1821 and the Mar phenotype was demonstrated both by the replacement of the wild-typemarR by marR ΔA1821 in isolate EP1 and by complementation with the wild-type marR intrans in isolate EP2. In isolate EP2 complemented with wild-type marR, susceptibility to chloramphenicol was restored completely, whereas susceptibility to CIP was restored only incompletely. Northern blotting demonstrated increased expression ofmarA and acrAB but not of soxS in isolate EP2 compared to EP1. In conclusion, the deletion of A1821 inmarR in the clinical isolate EP2 caused an increase in the MICs of CIP and unrelated antibiotics. Presumably, the C-terminal part of MarR is necessary for proper repressor function.

Resistance mechanisms ofEscherichia coli against fluoroquinolones (FQ) have been well studied, and three mechanisms have been identified. Point mutations in the quinolone resistance-determining regions (QRDRs) of topoisomerases II (gyrAB) and IV (parCE) lead to a stepwise acquisition of resistance (7, 9, 12). Active efflux of FQ by multidrug resistance pumps like AcrAB, and reduced uptake due to OmpF, both regulated by the transcription factor MarA, are also implicated in resistance (5, 18). These mechanisms, often in combination, have been found in strains from both in vitro and clinical investigations. However, few data are available about the development of resistance in patients, that is, the order of acquisition of the respective mechanisms and their contributions to the resistance phenotype. We investigated two clinical isolates of E. coli, with different levels of resistance to ciprofloxacin (CIP) but identical pulsed-field gel electrophoresis (PFGE) patterns, from one patient. By gene exchange and complementation we demonstrated the role of a C-terminal deletion in MarR resulting in increased efflux of FQ in the more resistant strain.

(This study was presented in part at the 39th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, Calif., 26 to 29 September, 1999.)

MATERIALS AND METHODS

Bacterial strains. E. coli isolates EP1 and EP2 were isolated from the vagina and the urine of a patient with generalized follicular lymphoma who had received 750 mg of CIP twice daily for selective decontamination of the gut. E. coli ATCC 25922 was obtained from the American Type Culture Collection (ATCC). E. coli EP2 acrA::Tn10-Km was obtained from the clinical isolate EP2 by transposon mutagenesis and screening for susceptibility against FQ. E. coli S17 λpir harboring the plasmid pLOF/Km was kindly donated by V. de Lorenzo (6). E. coli S17 containing plasmid pBP591 with wild-type marR has been described previously (V. Hüllen, P. Heisig, and B. Wiedemann, Abstr. 37th Intersci. Conf. Antimicrob. Agents Chemother., abstr. C-64, p. 57, 1997).

PFGE.A rapid PFGE procedure was performed as described previously (8). Macrorestriction was performed withXbaI at 37°C for 3 h. Electrophoresis was performed with the contour-clamped homogeneous electric field (CHEF) mapper system (Bio-Rad, Hercules, Calif.). The run time was 14 h, with an initial switch time of 2.16 s and a final switch time of 35 s.

Susceptibility testing.MICs of CIP were determined according to NCCLS recommendations for microdilution assays (16). MICs of chloramphenicol and tetracycline were determined by Etest (AB BIODISK, Solna, Sweden). For testing of organic solvent tolerance (OST), isolates were inoculated on Mueller-Hinton agar at a concentration of 105 CFU per spot and the plate was overlaid with hexane (H), cyclohexane (CH), and H-CH mixtures at ratios of 3:1, 1:1, and 1:3 to generate different levels of organic solvent toxicity. n-Hexane has a powof 3.9, and cyclohexane has a pow of 3.4 (3). The plates were checked for growth after 2 days.

DNA amplification and nucleotide sequence determination.Primers (Table 1) and PCR conditions for amplification of gyrA, gyrB, and parEwere used as previously described (7, 12). Primers and annealing temperatures for the amplification of parC, themar operon, marA and marB, andacrA are listed in Table 1. Complementary strands were sequenced in duplicate on a 310 DNA sequencer (Perkin-Elmer, Foster City, Calif.) using either PCR primer (6 μmol).

View this table:
  • View inline
  • View popup
Table 1.

Primers used in this study

Plasmids and DNA manipulations.Strains and plasmids used in this study are listed in Table 2. Introduction of the marR frameshift mutation from isolate EP2 into the wild-type marR of isolate EP1 required subcloning of the EcoRI/PstI-digested PCR fragment (with primers marR-f1452 and marR-r2229) into the corresponding pUC18 site to yield plasmid pmarR-ΔC18. Probes for Northern blot analysis were generated by subcloning of marA and soxS into plasmid pcDNA3 (Invitrogen, Groningen, The Netherlands) and in vitro transcription from the SP6 and T7 promoters, respectively. The completemarA gene (1893 to 2282) was amplified in a DNA thermocycler using primers marA-f1893 and marA-r2281. For the amplification and cloning of soxS, primers soxS-f331 and soxS-r1319were used. Genomic DNA from E. coli ATCC 25922 served as a template. The PCR fragments were cloned directionally into plasmid pcDNA3 to generate plasmids pc-marA and pc-soxS, respectively. Recombinant DNA techniques, transformation, and restriction enzyme digestions followed standard protocols (19).

View this table:
  • View inline
  • View popup
Table 2.

Bacterial strains and plasmids used in this study

Gene replacement.Introduction of the marRmutation into the wild-type marR gene of isolate EP1 was accomplished by homologous recombination between plasmid pmarR-ΔC18 and the bacterial chromosome, essentially as described previously (11). Plasmid pmarR-ΔC18 was introduced into isolate EP1 by electroporation (Genepulser; Bio-Rad). Resulting transformants were grown on Luria-Bertani (LB) agar plates supplemented with 50 mg of ampicillin/liter overnight at 37°C. Recombinant bacteria were then propagated in LB broth containing 32 mg of CIP/liter for selection ofE. coli carrying the desired recombination. Segregation of the plasmid after passaging of single colonies for 1 week was shown by growth inhibition of recombinant clones on LB agar plates containing ampicillin and by inability to amplify the specific marR DNA fragment by PCR with plasmid DNA preparations as templates using plasmid-specific primers.

Insertion mutagenesis.Transposon mutagenesis was performed using a suicide vector system as described previously (6, 10). The exconjugates were selected for reduced CIP MICs by transfer of single colonies to agar plates containing 64 or 2 μg of CIP/ml. Colonies growing selectively on plates with 2 μg of CIP/ml were further analyzed.

RNA extraction and Northern blot analysis.Overnight cultures were diluted 100-fold in LB broth and grown with shaking to mid-logarithmic phase at 37°C. Paraquat was added for the induction of the sox operon (45 min; final concentration, 1.3 mM; Sigma, Deisenhofen, Germany). For production of the marAprobe, plasmid pc-marA was linearized by HindIII digestion and in vitro RNA runoff transcription was performed with the RiboProbe Kit (Promega). Similarly, the soxS probe was obtained by XhoI digestion of plasmid pc-soxS and in vitro transcription. Digoxigenin (DIG)-labeled RNA probes were purified with the RNeasy Purification Kit (QIAGEN). The acrA probe was obtained by PCR. Northern blotting was performed using standard techniques (19).

Complementation assays.For the complementation of the mutant marR of isolate EP2, wild-type marR under the control of the bla promoter was introduced into isolate EP2 by mobilization with the filter mating technique. The donor strain,E. coli S17 carrying plasmid pBP591, and isolate EP2 were mixed in a 1:1 ratio and incubated at 37°C for 12 h on a minimal agar plate. Cells were resuspended in LB broth and plated on LB agar plates containing 50 μg of kanamycin/ml for selection.

Data analysis.SPSS 8.0 for Windows was used for calculation of Mann-Whitney U test results.

RESULTS AND DISCUSSION

PFGE typing generated identical patterns ofXbaI-digested total genomic DNA for isolates EP1 and EP2 but different patterns for three epidemiologically unrelated strains used as a control. Further evidence for the high genetic relatedness of the two isolates was given by the finding of a 61-bp deletion and a 785-bp insertion at the same site in both strains between bp 1252 and 1313 of the published mar wild-type sequence (4) and by observation of identical patterns in randomly primed PCR using five different primers (data not shown).

The MICs of CIP for EP1 and EP2 were different, 16 and 256 mg/liter, respectively; however, identical changes in critical residues of the QRDRs of gyrA (Ser83Leu, Asp87Tyr) and parC(Ser80Ile) were found. This combination of amino acid alterations in critical residues can explain a CIP MIC of 16 mg/liter (12); however, no other substitutions in the QRDR of gyrB orparE were detected in any strain.

Compared to EP1, EP2 also required higher MICs of chloramphenicol (32 versus 4 mg/liter), tetracycline (32 versus 8 mg/liter), and cefuroxime (>16 versus 4 mg/liter), and EP2 but not EP1 grew on Mueller-Hinton agar overlaid with hexane or a 3:1 hexane-cyclohexane mixture. These properties of EP2 were consistent with a Mar phenotype, and consequently increased expression of the marA transcript was demonstrated by Northern blotting (Fig.1A). Increased expression was demonstrated independently by quantitative PCR using TaqMan technology after a reverse PCR step (data not shown). Compared to wild-type transcription of marA in strain ATCC 25922, transcription ofmarA in isolate EP2 was estimated to be 64-fold, as determined by twofold serial dilutions of the target sequence of isolate EP2 (Fig. 1B). Expression of soxS, another transcription factor of the acr locus (15), with and without stimulation with paraquat, was similar in both isolates (Northern blot, data not shown). The increased transcription ofmarA in isolate EP2 led to increased expression ofacrA, as could be expected (1). In theacrA Northern blot, two transcripts of approximately 4.5 and 2.2 kb were observed (Fig. 2). The size of the larger transcript corresponds to the expected length of theacrAB transcript of 4.344 kb, and this transcript is also dominant. Sequencing of the mar operons of isolates EP1 and EP2 indicated a deletion of adenine 1821 of marR in EP2. This deletion resulted in a frameshift and a concomitant loss of 18 amino acids in the C-terminal region of the MarR protein.

Fig. 1.
  • Open in new tab
  • Download powerpoint
Fig. 1.

Northern blot analyses of marA. (A) Total RNA of E. coli was prepared, transferred to Hybond-N+ membranes, and probed with DIG-labeledmarR RNA. The prominent transcripts and Boehringer RNA molecular weight standard III are indicated. (B) A twofold serial dilution of total RNA of E. coli isolate EP2 and undiluted RNAs from E. coli isolate EP1 and strain ATCC 25922 were transferred to Hybond-N+ membranes, stained with methylene blue, and probed with DIG-labeled marR RNA.

Fig. 2.
  • Open in new tab
  • Download powerpoint
Fig. 2.

Northern blot analysis of acrAB. Total RNA was prepared, transferred to Hybond-N+ membranes and probed with DIG-labeled acrA PCR product. The prominent transcript and Boehringer RNA molecular weight standard II are indicated.

To investigate the possible role of the truncation of MarR, gene exchange and complementation experiments were designed. When we introduced the defective marR into the chromosomal DNA of isolate EP1 by homologous recombination, the MIC of CIP rose to 64 to 128 mg/liter, suggesting diminished repressor activity of the truncated MarR. Likewise, in isolate EP2, in trans complementation with the wild-type marR resulted in a lower CIP MIC of 64 mg/liter. The putative role of the frameshift in marRaffecting the regulation of transcription of the AcrAB efflux pump was corroborated by the knockout mutant EP2acrA::Tn10-Km, for which the MIC of CIP fell back to 32 mg/liter. The characteristics of EP1, EP2, and their derivatives are summarized in Table 3.

View this table:
  • View inline
  • View popup
Table 3.

Characteristics of E. coli ATCC 25922, EP1, EP2, EP2 acrA::Tn10-Km, EP1 ΔmarR, and EP2 complemented with wild-type marR

Neither the introduction of the wild-type marR into isolate EP2 nor the introduction of the defective marR into isolate EP1 resulted in a complete reversal of CIP MICs, indicating an additional, yet unknown resistance mechanism(s). The presence of additional resistance mechanisms is also suggested by the author of a recent study of E. coli with GyrA and MarA mutations generated in vitro, in which no clinically relevant resistance to CIP was detectable in acrAB knockout mutants (17). Efflux pump inhibitors, which restored susceptibility to FQ in the presence of target mutations (13), may not be effective in the E. coli clinical isolate EP2 analyzed in this study.

The multiple antibiotic resistance locus (mar) of E. coli controls intrinsic susceptibility to multiple antibiotics, organic solvents, oxidative stress agents, and the disinfectant triclosan (for reviews see references 1, 2, and14). Presumably, the N-terminal and central regions of MarR, where a helix-turn-helix motif has been identified, are responsible for the specific interactions with the two binding sites inmarO (1). The finding of this study indicates that the C terminus of MarR is also necessary for proper repressor function.

In conclusion, using genetic exchange and complementation techniques in an otherwise genetically indistinguishable pair of clinical isolates ofE. coli, we have identified a unique C-terminal deletion in MarR resulting in a Mar phenotype affecting the MICs of FQ, tetracycline, chloramphenicol, and cefuroxime, as well as OST. Changes in the target enzyme and active efflux both add to the resistance phenotype. This is yet another example of the versatility of bacterial acquisition of antimicrobial resistance.

ACKNOWLEDGMENTS

We gratefully acknowledge the technical assistance of Emmi Fuchs and Christine Irtenkauf. Nucleotide sequence determination was performed by Holger Melzl and Josef Köstler.

FOOTNOTES

    • Received 24 November 1999.
    • Returned for modification 28 January 2000.
    • Accepted 21 April 2000.
  • Copyright © 2000 American Society for Microbiology

REFERENCES

  1. 1.↵
    1. Alekshun M. N.,
    2. Levy S. B.
    Regulation of chromosomally mediated multiple antibiotic resistance: the mar regulon. Antimicrob. Agents Chemother. 41 1997 2067 2075
    OpenUrlFREE Full Text
  2. 2.↵
    1. Alekshun M. N.,
    2. Levy S. B.
    The mar regulon: multiple resistance to antibiotics and other toxic chemicals. Trends Microbiol. 7 1999 410 413
    OpenUrlCrossRefPubMedWeb of Science
  3. 3.↵
    1. Aono R.
    Improvement of organic solvent tolerance level of Escherichia coli by overexpression of stress-responsive genes. Extremophiles 2 1998 239 248
    OpenUrlCrossRefPubMed
  4. 4.↵
    1. Cohen S. P.,
    2. Hachler H.,
    3. Levy S. B.
    Genetic and functional analysis of the multiple antibiotic resistance (mar) locus in Escherichia coli. J. Bacteriol. 175 1993 1484 1492
    OpenUrlAbstract/FREE Full Text
  5. 5.↵
    1. Cohen S. P.,
    2. McMurry L. M.,
    3. Hooper D. C.,
    4. Wolfson J. S.,
    5. Levy S. B.
    Cross-resistance to fluoroquinolones in multiple-antibiotic-resistant (Mar) Escherichia coli selected by tetracycline or chloramphenicol: decreased drug accumulation associated with membrane changes in addition to OmpF reduction. Antimicrob. Agents Chemother. 33 1989 1318 1325
    OpenUrlAbstract/FREE Full Text
  6. 6.↵
    1. de Lorenzo V.,
    2. Timmis K. N.
    Analysis and construction of stable phenotypes in gram-negative bacteria with Tn5- and Tn10-derived minitransposons. Methods Enzymol. 235 1994 386 405
    OpenUrlCrossRefPubMedWeb of Science
  7. 7.↵
    1. Everett M. J.,
    2. Jin Y. F.,
    3. Ricci V.,
    4. Piddock L. J.
    Contributions of individual mechanisms to fluoroquinolone resistance in 36 Escherichia coli strains isolated from humans and animals. Antimicrob. Agents Chemother. 40 1996 2380 2386
    OpenUrlAbstract/FREE Full Text
  8. 8.↵
    1. Gautom R. K.
    Rapid pulsed-field gel electrophoresis protocol for typing of Escherichia coli O157:H7 and other gram-negative organisms in 1 day. J. Clin. Microbiol. 35 1997 2977 2980
    OpenUrlAbstract/FREE Full Text
  9. 9.↵
    1. Heisig P.
    Genetic evidence for a role of parC mutations in development of high-level fluoroquinolone resistance in Escherichia coli. Antimicrob. Agents Chemother. 40 1996 879 885
    OpenUrlAbstract/FREE Full Text
  10. 10.↵
    1. Herrero M.,
    2. de Lorenzo V.,
    3. Timmis K. N.
    Transposon vectors containing non-antibiotic resistance selection markers for cloning and stable chromosomal insertion of foreign genes in gram-negative bacteria. J. Bacteriol. 172 1990 6557 6567
    OpenUrlAbstract/FREE Full Text
  11. 11.↵
    1. Kiel J. A.,
    2. Vossen J. P.,
    3. Venema G.
    A general method for the construction of Escherichia coli mutants by homologous recombination and plasmid segregation. Mol. Gen. Genet. 207 1987 294 301
    OpenUrlCrossRefPubMed
  12. 12.↵
    1. Lehn N.,
    2. Stoewer-Hoffmann J.,
    3. Kott T.,
    4. Strassner C.,
    5. Wagner H.,
    6. Schneider-Brachert W.
    Characterization of clinical isolates of Escherichia coli showing high levels of fluoroquinolone resistance. J. Clin. Microbiol. 34 1996 597 602
    OpenUrlAbstract/FREE Full Text
  13. 13.↵
    1. Lomovskaya O.,
    2. Lee A.,
    3. Hoshino K.,
    4. Ishida H.,
    5. Mistry A.,
    6. Warren M. S.,
    7. Boyer E.,
    8. Chamberland S.,
    9. Lee V. J.
    Use of a genetic approach to evaluate the consequences of inhibition of efflux pumps in Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 43 1999 1340 1346
    OpenUrlAbstract/FREE Full Text
  14. 14.↵
    1. McMurry L. M.,
    2. Oethinger M.,
    3. Levy S. B.
    Overexpression of marA,soxS, or acrAB produces resistance to triclosan in laboratory and clinical strains of Escherichia coli. FEMS Microbiol. Lett. 166 1998 305 309
    OpenUrlCrossRefPubMedWeb of Science
  15. 15.↵
    1. Miller P. F.,
    2. Sulavik M. C.
    Overlaps and parallels in the regulation of intrinsic multiple-antibiotic resistance in Escherichia coli. Mol. Microbiol. 21 1996 441 448
    OpenUrlCrossRefPubMedWeb of Science
  16. 16.↵
    National Committee for Clinical Laboratory Standards Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically 4th ed. 1997 Approved standard. NCCLS document M7-A4. National Committee for Clinical Laboratory Standards, Wayne, Pa.
  17. 17.↵
    1. Oethinger M.,
    2. Kern W. V.,
    3. Jellen-Ritter A. S.,
    4. McMurry L. M.,
    5. Levy S. B.
    Ineffectiveness of topoisomerase mutations in mediating clinically significant fluoroquinolone resistance in Escherichia coli in the absence of the AcrAB efflux pump. Antimicrob. Agents Chemother. 44 2000 10 13
    OpenUrlAbstract/FREE Full Text
  18. 18.↵
    1. Oethinger M.,
    2. Podglajen I.,
    3. Kern W. V.,
    4. Levy S. B.
    Overexpression of the marA or soxS regulatory gene in clinical topoisomerase mutants of Escherichia coli. Antimicrob. Agents Chemother. 42 1998 2089 2094
    OpenUrlAbstract/FREE Full Text
  19. 19.↵
    1. Sambrook J.,
    2. Fritsch E. F.,
    3. Maniatis T.
    Molecular cloning: a laboratory manual 2nd ed. 1989 Cold Spring Harbor Laboratory Press Cold Spring Harbor, N.Y
View Abstract
PreviousNext
Back to top
Download PDF
Citation Tools
In Vivo Increase in Resistance to Ciprofloxacin inEscherichia coli Associated with Deletion of the C-Terminal Part of MarR
Hans-Jörg Linde, Frank Notka, Michaela Metz, Bernd Kochanowski, Peter Heisig, Norbert Lehn
Antimicrobial Agents and Chemotherapy Jul 2000, 44 (7) 1865-1868; DOI: 10.1128/AAC.44.7.1865-1868.2000

Citation Manager Formats

  • BibTeX
  • Bookends
  • EasyBib
  • EndNote (tagged)
  • EndNote 8 (xml)
  • Medlars
  • Mendeley
  • Papers
  • RefWorks Tagged
  • Ref Manager
  • RIS
  • Zotero
Print

Alerts
Sign In to Email Alerts with your Email Address
Email

Thank you for sharing this Antimicrobial Agents and Chemotherapy article.

NOTE: We request your email address only to inform the recipient that it was you who recommended this article, and that it is not junk mail. We do not retain these email addresses.

Enter multiple addresses on separate lines or separate them with commas.
In Vivo Increase in Resistance to Ciprofloxacin inEscherichia coli Associated with Deletion of the C-Terminal Part of MarR
(Your Name) has forwarded a page to you from Antimicrobial Agents and Chemotherapy
(Your Name) thought you would be interested in this article in Antimicrobial Agents and Chemotherapy.
CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
Share
In Vivo Increase in Resistance to Ciprofloxacin inEscherichia coli Associated with Deletion of the C-Terminal Part of MarR
Hans-Jörg Linde, Frank Notka, Michaela Metz, Bernd Kochanowski, Peter Heisig, Norbert Lehn
Antimicrobial Agents and Chemotherapy Jul 2000, 44 (7) 1865-1868; DOI: 10.1128/AAC.44.7.1865-1868.2000
del.icio.us logo Digg logo Reddit logo Twitter logo CiteULike logo Facebook logo Google logo Mendeley logo
  • Top
  • Article
    • ABSTRACT
    • MATERIALS AND METHODS
    • RESULTS AND DISCUSSION
    • ACKNOWLEDGMENTS
    • FOOTNOTES
    • REFERENCES
  • Figures & Data
  • Info & Metrics
  • PDF

KEYWORDS

anti-infective agents
Bacterial Proteins
ciprofloxacin
Escherichia coli
Escherichia coli Proteins
Repressor Proteins

Related Articles

Cited By...

About

  • About AAC
  • Editor in Chief
  • Editorial Board
  • Policies
  • For Reviewers
  • For the Media
  • For Librarians
  • For Advertisers
  • Alerts
  • AAC Podcast
  • RSS
  • FAQ
  • Permissions
  • Journal Announcements

Authors

  • ASM Author Center
  • Submit a Manuscript
  • Article Types
  • Ethics
  • Contact Us

Follow #AACJournal

@ASMicrobiology

       

ASM Journals

ASM journals are the most prominent publications in the field, delivering up-to-date and authoritative coverage of both basic and clinical microbiology.

About ASM | Contact Us | Press Room

 

ASM is a member of

Scientific Society Publisher Alliance

 

American Society for Microbiology
1752 N St. NW
Washington, DC 20036
Phone: (202) 737-3600

Copyright © 2021 American Society for Microbiology | Privacy Policy | Website feedback

Print ISSN: 0066-4804; Online ISSN: 1098-6596