The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
L. Mark Fisher - One of the best experts on this subject based on the ideXlab platform.
-
DNA Gyrase and Topoisomerase IV Are Dual Targets of Clinafloxacin Action in Streptococcus pneumoniae
Antimicrobial Agents and Chemotherapy, 1998Co-Authors: Xiao-su Pan, L. Mark FisherAbstract:We examined the response of Streptococcus pneumoniae 7785 to clinafloxacin, a novel C-8-substituted fluoroquinolone which is being developed as an antipneumococcal agent. Clinafloxacin was highly active against S. pneumoniae 7785 (MIC, 0.125 μg/ml), and neither gyrA nor parC quinolone resistance mutations alone had much effect on this activity. A combination of both mutations was needed to register resistance, suggesting that both gyrase and topoisomerase IV are clinafloxacin targets in vivo. The sparfloxacin and ciprofloxacin MICs for the parC-gyrA mutants were 16 to 32 and 32 to 64 μg/ml, respectively, but the clinafloxacin MIC was 1 μg/ml, i.e., within clinafloxacin levels achievable in human serum. S. pneumoniae 7785 mutants could be selected stepwise with clinafloxacin at a low frequency, yielding first-, second-, third-, and fourth-step mutants for which clinafloxacin MICs were 0.25, 1, 6, and 32 to 64 μg/ml, respectively. Thus, high-level resistance to clinafloxacin required four steps. Characterization of the quinolone resistance-determining regions of the gyrA , parC , gyrB , and parE genes by PCR, Hin fI restriction fragment length polymorphism, and DNA sequence analysis revealed an invariant resistance pathway involving sequential mutations in gyrA or gyrB , in parC , in gyrA , and finally in parC or parE . No evidence was found for other resistance mechanisms. The gyrA mutations in first- and third-step mutants altered GyrA hot spots Ser-83 to Phe or Tyr ( Escherichia coli coordinates) and Glu-87 to Gln or Lys; second- and fourth-step parC mutations changed equivalent hot spots Ser-79 to Phe or Tyr and Asp-83 to Ala. gyrB and parE changes produced novel alterations of GyrB Glu-474 to Lys and of Pro-454 to Ser in the ParE PLRGK motif. Difficulty in selecting first-step gyrase mutants (isolated with 0.125 [but not 0.25] μg of clinafloxacin per ml at a frequency of 5.0 × 10 −10 to 8.5 × 10 −10 ) accompanied by the small (twofold) MIC increase suggested only a modest drug preference for gyrase. Given the susceptibility of defined gyrA or parC mutants, the results suggested that clinafloxacin displays comparable if unequal targeting of gyrase and topoisomerase IV. Dual targeting and the intrinsic potency of clinafloxacin against S. pneumoniae and its first- and second-step mutants are desirable features in limiting the emergence of bacterial resistance.
-
involvement of topoisomerase iv and dna gyrase as ciprofloxacin targets in streptococcus pneumoniae
Antimicrobial Agents and Chemotherapy, 1996Co-Authors: Xiao-su Pan, J Ambler, S Mehtar, L. Mark FisherAbstract:Ciprofloxacin-resistant mutants of Streptococcus pneumoniae 7785 were generated by stepwise selection at increasing drug concentrations. Sequence analysis of PCR products from the strains was used to examine the quinolone resistance-determining regions of the GyrA and GyrB proteins of DNA gyrase and the analogous regions of the ParC and ParE subunits of DNA topoisomerase IV. First-step mutants exhibiting low-level resistance had no detectable changes in their topoisomerase quinolone resistance-determining regions, suggesting altered permeation or another novel resistance mechanism. Nine of 10 second-step mutants exhibited an alteration in ParC at Ser-79 to Tyr or Phe or at Ala-84 to Thr. Third- and fourth-step mutants displaying high-level ciprofloxacin resistance were found to have, in addition to the ParC alteration, a change in GyrA at residues equivalent to Escherichia coli GyrA resistance hot spots Ser-83 and Asp-87 or in GyrB at Asp-435 to Asn, equivalent to E. coli Asp-426, part of a highly conserved EGDSA motif in GyrB. No ParE changes were observed. Complementary analysis of two S. pneumoniae clinical isolates displaying low-level resistance to ciprofloxacin revealed a ParC change at Ser-79 to Phe or Arg-95 to Cys but no changes in GyrA, GyrB, or ParE. A highly resistant isolate, in addition to a ParC mutation, had a GyrA alteration at the residue equivalent to E. coli Asp-87. Thus, in both laboratory strains and clinical isolates, ParC mutations preceded those in GyrA, suggesting that topoisomerase IV is a primary topoisomerase target and gyrase is a secondary target for ciprofloxacin in S. pneumoniae.
Fred C Tenove - One of the best experts on this subject based on the ideXlab platform.
-
dna gyrase and topoisomerase iv mutations associated with fluoroquinolone resistance in proteus mirabilis
Antimicrobial Agents and Chemotherapy, 2002Co-Authors: Linda M Weigel, Gregory J Anderso, Fred C TenoveAbstract:Mutations associated with fluoroquinolone resistance in clinical isolates of Proteus mirabilis were determined by genetic analysis of the quinolone resistance-determining region (QRDR) of gyrA, gyrB, parC, and parE. This study included the P. mirabilis type strain ATCC 29906 and 29 clinical isolates with reduced susceptibility (MIC, 0.5 to 2 μg/ml) or resistance (MIC, ≥4 μg/ml) to ciprofloxacin. Susceptibility profiles for ciprofloxacin, clinafloxacin, gatifloxacin, gemifloxacin, levofloxacin, moxifloxacin, and trovafloxacin were correlated with amino acid changes in the QRDRs. Decreased susceptibility and resistance were associated with double mutations involving both gyrA (S83R or -I) and parC (S80R or -I). Among these double mutants, MICs of ciprofloxacin varied from 1 to 16 μg/ml, indicating that additional factors, such as drug efflux or porin changes, also contribute to the level of resistance. For ParE, a single conservative change of V364I was detected in seven strains. An unexpected result was the association of gyrB mutations with high-level resistance to fluoroquinolones in 12 of 20 ciprofloxacin-resistant isolates. Changes in GyrB included S464Y (six isolates), S464F (three isolates), and E466D (two isolates). A three-nucleotide insertion, resulting in an additional lysine residue between K455 and A456, was detected in gyrB of one strain. Unlike any other bacterial species analyzed to date, mutation of gyrB appears to be a frequent event in the acquisition of fluoroquinolone resistance among clinical isolates of P. mirabilis.
Haruo Watanabe - One of the best experts on this subject based on the ideXlab platform.
-
fluoroquinolone resistance linked to both gyra and parc mutations in the quinolone resistance determining region of shigella dysenteriae type 1
Current Microbiology, 2006Co-Authors: Kaisar A Talukder, Haruo Watanabe, Bijay K Khajanchi, Mohammad Aminul Islam, Zhahirul Islam, Dilip K Dutta, Mustafizur Rahman, G B Nair, David Allen SackAbstract:We examined the quinolone resistance–determining region (QRDR) of gyrA, gyrB, and parC of recently isolated fluoroquinolone-resistant S. dysenteriae type 1 strains from south Asia and compared data with fluoroquinolone-susceptible strains associated with previous epidemics of 1978, 1984, and 1994. In fluoroquinolone-resistant strains, double mutations (Ser83 → Leu, Asp87 → Asn or Gly) and a single mutation (Ser80 → Ile) were detected in the QRDRs of gyrA and parC, respectively.
-
dna sequence analysis of dna gyrase and dna topoisomerase iv quinolone resistance determining regions of salmonella enterica serovar typhi and serovar paratyphi a
Antimicrobial Agents and Chemotherapy, 2002Co-Authors: Kenji Hirose, Ai Hashimoto, Kazumichi Tamura, Yoshiaki Kawamura, Takayuki Ezaki, Hiroko Sagara, Haruo WatanabeAbstract:The mutations that are responsible for fluoroquinolone resistance in the gyrA, gyrB, parC, and parE genes of Salmonella enterica serovar Typhi and serovar Paratyphi A were investigated. The sequences of the quinolone resistance-determining region of the gyrA gene in clinical isolates which showed decreased susceptibilities to fluoroquinolones had a single mutation at either the Ser-83 or the Asp-87 codon, and no mutations were found in the gyrB, parC, and parE genes.
Xiao-su Pan - One of the best experts on this subject based on the ideXlab platform.
-
DNA Gyrase and Topoisomerase IV Are Dual Targets of Clinafloxacin Action in Streptococcus pneumoniae
Antimicrobial Agents and Chemotherapy, 1998Co-Authors: Xiao-su Pan, L. Mark FisherAbstract:We examined the response of Streptococcus pneumoniae 7785 to clinafloxacin, a novel C-8-substituted fluoroquinolone which is being developed as an antipneumococcal agent. Clinafloxacin was highly active against S. pneumoniae 7785 (MIC, 0.125 μg/ml), and neither gyrA nor parC quinolone resistance mutations alone had much effect on this activity. A combination of both mutations was needed to register resistance, suggesting that both gyrase and topoisomerase IV are clinafloxacin targets in vivo. The sparfloxacin and ciprofloxacin MICs for the parC-gyrA mutants were 16 to 32 and 32 to 64 μg/ml, respectively, but the clinafloxacin MIC was 1 μg/ml, i.e., within clinafloxacin levels achievable in human serum. S. pneumoniae 7785 mutants could be selected stepwise with clinafloxacin at a low frequency, yielding first-, second-, third-, and fourth-step mutants for which clinafloxacin MICs were 0.25, 1, 6, and 32 to 64 μg/ml, respectively. Thus, high-level resistance to clinafloxacin required four steps. Characterization of the quinolone resistance-determining regions of the gyrA , parC , gyrB , and parE genes by PCR, Hin fI restriction fragment length polymorphism, and DNA sequence analysis revealed an invariant resistance pathway involving sequential mutations in gyrA or gyrB , in parC , in gyrA , and finally in parC or parE . No evidence was found for other resistance mechanisms. The gyrA mutations in first- and third-step mutants altered GyrA hot spots Ser-83 to Phe or Tyr ( Escherichia coli coordinates) and Glu-87 to Gln or Lys; second- and fourth-step parC mutations changed equivalent hot spots Ser-79 to Phe or Tyr and Asp-83 to Ala. gyrB and parE changes produced novel alterations of GyrB Glu-474 to Lys and of Pro-454 to Ser in the ParE PLRGK motif. Difficulty in selecting first-step gyrase mutants (isolated with 0.125 [but not 0.25] μg of clinafloxacin per ml at a frequency of 5.0 × 10 −10 to 8.5 × 10 −10 ) accompanied by the small (twofold) MIC increase suggested only a modest drug preference for gyrase. Given the susceptibility of defined gyrA or parC mutants, the results suggested that clinafloxacin displays comparable if unequal targeting of gyrase and topoisomerase IV. Dual targeting and the intrinsic potency of clinafloxacin against S. pneumoniae and its first- and second-step mutants are desirable features in limiting the emergence of bacterial resistance.
-
involvement of topoisomerase iv and dna gyrase as ciprofloxacin targets in streptococcus pneumoniae
Antimicrobial Agents and Chemotherapy, 1996Co-Authors: Xiao-su Pan, J Ambler, S Mehtar, L. Mark FisherAbstract:Ciprofloxacin-resistant mutants of Streptococcus pneumoniae 7785 were generated by stepwise selection at increasing drug concentrations. Sequence analysis of PCR products from the strains was used to examine the quinolone resistance-determining regions of the GyrA and GyrB proteins of DNA gyrase and the analogous regions of the ParC and ParE subunits of DNA topoisomerase IV. First-step mutants exhibiting low-level resistance had no detectable changes in their topoisomerase quinolone resistance-determining regions, suggesting altered permeation or another novel resistance mechanism. Nine of 10 second-step mutants exhibited an alteration in ParC at Ser-79 to Tyr or Phe or at Ala-84 to Thr. Third- and fourth-step mutants displaying high-level ciprofloxacin resistance were found to have, in addition to the ParC alteration, a change in GyrA at residues equivalent to Escherichia coli GyrA resistance hot spots Ser-83 and Asp-87 or in GyrB at Asp-435 to Asn, equivalent to E. coli Asp-426, part of a highly conserved EGDSA motif in GyrB. No ParE changes were observed. Complementary analysis of two S. pneumoniae clinical isolates displaying low-level resistance to ciprofloxacin revealed a ParC change at Ser-79 to Phe or Arg-95 to Cys but no changes in GyrA, GyrB, or ParE. A highly resistant isolate, in addition to a ParC mutation, had a GyrA alteration at the residue equivalent to E. coli Asp-87. Thus, in both laboratory strains and clinical isolates, ParC mutations preceded those in GyrA, suggesting that topoisomerase IV is a primary topoisomerase target and gyrase is a secondary target for ciprofloxacin in S. pneumoniae.
Vibha Tandon - One of the best experts on this subject based on the ideXlab platform.
-
Contribution of mutations in DNA gyrase and topoisomerase IV genes to ciprofloxacin resistance in Escherichia coli clinical isolates.
International journal of antimicrobial agents, 2011Co-Authors: Sandhya Bansal, Vibha TandonAbstract:DNA gyrase (GyrA and GyrB) and topoisomerase IV (ParC and ParE) are the two essential type II topoisomerases in Escherichia coli. These enzymes act via inhibition of DNA replication. Mutations in the quinolone resistance-determining region (QRDR) of the gyrA, gyrB, parC and parE genes from clinical isolates of E. coli were determined by DNA sequencing of 54 ciprofloxacin-resistant clinical isolates from a hospital in Delhi, India. The majority of the E. coli isolates were shown to carry mutations in gyrA, parC and parE. Ciprofloxacin resistance due to accumulation of such a high number of mutations in the QRDR regions of gyrA at positions Ser83 and Asp87 and parC at position Ser80 as well as outside of the QRDR region of parE at Ser458 and Glu460 confers high-level resistance of ciprofloxacin in clinical isolates. The high frequency of occurrence of mutations in the parE gene (44.4% strains) is alarming, as topoisomerase IV is a secondary target of quinolones.
