Antipneumococcal activity of DW-224a, a new quinolone, compared to those of eight other agents

DW-224a is a new broad-spectrum quinolone with excellent antipneumococcal activity. Agar dilution MIC was used to test the activity of DW-224a compared to those of penicillin, ciprofloxacin, levofloxacin, gatifloxacin, moxifloxacin, gemifloxacin, amoxicillin-clavulanate, cefuroxime, and azithromycin against 353 quinolone-susceptible pneumococci. The MICs of 29 quinolone-resistant pneumococci with defined quinolone resistance mechanisms against seven quinolones and an efflux mechanism were also tested. DW-224a was the most potent quinolone against quinolone-susceptible pneumococci (MIC(50), 0.016 microg/ml; MIC(90), 0.03 microg/ml), followed by gemifloxacin, moxifloxacin, gatifloxacin, levofloxacin, and ciprofloxacin. beta-Lactam MICs rose with those of penicillin G, and azithromycin resistance was seen mainly in strains with raised penicillin G MICs. Against the 29 quinolone-resistant strains, DW-224a had the lowest MICs (0.06 to 1 microg/ml) compared to those of gemifloxacin, clinafloxacin, moxifloxacin, gatifloxacin, levofloxacin, and ciprofloxacin. DW-224a at 2x MIC was bactericidal after 24 h against eight of nine strains tested. Other quinolones gave similar kill kinetics relative to higher MICs. Serial passages of nine strains in the presence of sub-MIC concentrations of DW-224a, moxifloxacin, levofloxacin, ciprofloxacin, gatifloxacin, gemifloxacin, amoxicillin-clavulanate, cefuroxime, and azithromycin were performed. DW-224a yielded resistant clones similar to moxifloxacin and gemifloxacin but also yielded lower MICs. Azithromycin selected resistant clones in three of the five parents tested. Amoxicillin-clavulanate and cefuroxime did not yield resistant clones after 50 days.     

In vitro and in vivo antibacterial activities of DK-507k, a novel fluoroquinolone

The antibacterial activities of DK-507k, a novel quinolone, were compared with those of other quinolones: ciprofloxacin, gatifloxacin, levofloxacin, moxifloxacin, sitafloxacin, and garenoxacin (BMS284756). DK-507k was as active as sitafloxacin and was as active as or up to eightfold more active than gatifloxacin, moxifloxacin, and garenoxacin against Streptococcus pneumoniae, methicillin-susceptible and methicillin-resistant Staphylococcus aureus, and coagulase-negative staphylococci. DK-507k was as active as or 4-fold more active than garenoxacin and 2- to 16-fold more active than gatifloxacin and moxifloxacin against ciprofloxacin-resistant strains of S. pneumoniae, including clinical isolates and in vitro-selected mutants with known mutations. DK-507k inhibited all ciprofloxacin-resistant strains of S. pneumoniae at 1 microg/ml. A time-kill assay with S. pneumoniae showed that DK-507k was more bactericidal than gatifloxacin and moxifloxacin. The activities of DK-507k against most members of the family Enterobacteriaceae were comparable to those of ciprofloxacin and equal to or up to 32-fold higher than those of gatifloxacin, levofloxacin, moxifloxacin, and garenoxacin. DK-507k was fourfold less active than sitafloxacin and ciprofloxacin against Pseudomonas aeruginosa, while it was two to four times more potent than levofloxacin, gatifloxacin, moxifloxacin, and garenoxacin against P. aeruginosa. In vivo, intravenous treatment with DK-507k was more effective than that with gatifloxacin and moxifloxacin against systemic infections caused by S. aureus, S. pneumoniae, and P. aeruginosa in mice. In a mouse model of pneumonia due to penicillin-resistant S. pneumoniae, DK-507k administered subcutaneously showed dose-dependent efficacy and eliminated the bacteria from the lungs, whereas gatifloxacin and moxifloxacin had no significant efficacy. Oral treatment with DK-507k was slightly more effective than that with ciprofloxacin in a rat model of foreign body-associated urinary tract infection caused by a P. aeruginosa isolate for which the MIC of DK-507k was fourfold higher than that of ciprofloxacin. Oral administration of DK-507k to rats achieved higher peak concentrations in serum and higher concentrations in cumulative urine than those achieved with ciprofloxacin. These data indicate the potential advantages of DK-507k over other quinolones for the treatment of a wide range of community-acquired infections.     

Antistaphylococcal activity of DX-619, a new des-F(6)-quinolone, compared to those of other agents

The in vitro activity of DX-619, a new des-F(6)-quinolone, was tested against staphylococci and compared to those of other antimicrobials. DX-619 had the lowest MIC ranges/MIC(50)s/MIC(90)s (microg/ml) against 131 Staphylococcus aureus strains (32), and ciprofloxacin (>32/>32). Raised quinolone MICs were associated with mutations in GyrA (S84L) and single or double mutations in GrlA (S80F or Y; E84K, G, or V) in all S. aureus strains tested. A recent vancomycin-resistant S. aureus (VRSA) strain (Hershey) was resistant to available quinolones and was inhibited by DX-619 at 0.25 microg/ml and sitafloxacin at 1.0 microg/ml. Vancomycin (except VRSA), linezolid, ranbezolid, tigecycline, and quinupristin-dalfopristin were active against all strains, and teicoplanin was active against S. aureus but less active against coagulase-negative staphylococci. DX-619 produced resistant mutants with MICs of 1 to >32 microg/ml after <50 days of selection compared to 16 to >32 microg/ml for ciprofloxacin, sitafloxacin, moxifloxacin, and gatifloxacin. DX-619 and sitafloxacin were also more active than other tested drugs against selected mutants and had the lowest mutation frequencies in single-step resistance selection. DX-619 and sitafloxacin were bactericidal against six quinolone-resistant (including the VRSA) and seven quinolone-susceptible strains tested, whereas gatifloxacin, moxifloxacin, levofloxacin, and ciprofloxacin were bactericidal against 11, 10, 7, and 5 strains at 4x MIC after 24 h, respectively. DX-619 was also bactericidal against one other VRSA strain, five vancomycin-intermediate S. aureus strains, and four vancomycin-intermediate coagulase-negative staphylococci. Linezolid, ranbezolid, and tigecycline were bacteriostatic and quinupristin-dalfopristin, teicoplanin, and vancomycin were bactericidal against two, eight, and nine strains, and daptomycin and oritavancin were rapidly bactericidal against all strains, including the VRSA. DX-619 has potent in vitro activity against staphylococci, including methicillin-, ciprofloxacin-, and vancomycin-resistant strains.     

Single- and multi-step resistance selection study of gemifloxacin compared with trovafloxacin, ciprofloxacin, gatifloxacin and moxifloxacin in Streptococcus pneumoniae

The ability of sequential subcultures in subinhibitory concentrations of gemifloxacin, trovafloxacin, ciprofloxacin, gatifloxacin and moxifloxacin to select resistant mutants was studied in 16 pneumococci [eight with ciprofloxacin MICs (mg/L) 0.25-1; four with 8-16; four with 16-32]. Subculturing was done 50 times, or until mutants with elevated MICs (> or = 4 x) to the selecting drug emerged. Subculturing in gemifloxacin selected six resistant mutants (gemifloxacin MICs 2 mg/L); trovafloxacin selected nine (trovafloxacin MICs 2-4 mg/L); ciprofloxacin selected 11 (ciprofloxacin MICs 8-128 mg/L); gatifloxacin selected 13; and moxifloxacin selected 12 (gatifloxacin or moxifloxacin MICs 2-16 mg/L). DNA sequencing showed that most mutants had mutations in ParC at Ser-79 or Asp-83 and in GyrA at Ser-81 or Glu-85; some mutants also had mutations in ParE or GyrB. Some new mutations were found in ParE or GyrB that have not yet been reported; GyrB mutation might be associated with moxifloxacin resistance. Both DNA gyrase and topoisomerase IV were thought to be the target of gemifloxacin; gemifloxacin also selected mutants with single modifications in gyrA, parC or parE alone among derived mutants by repeated exposure to subinhibitory concentrations of fluoroquinolones. In the presence of reserpine, most mutants had lower MICs of ciprofloxacin and gemifloxacin (4-32 x), and gatifloxacin (4-8 x), suggesting an efflux mechanism; none had lower trovafloxacin and moxifloxacin MICs. All quinolones tested selected for resistance; judicious use and proper dosing will be necessary to avoid resistance selection of newer broad-spectrum fluoroquinolones.     

Activities of Trovafloxacin Compared with Those of Other Fluoroquinolones against Purified Topoisomerases and gyrA and grlA Mutants of Staphylococcus aureus

Frequencies of mutation to resistance with trovafloxacin and four other quinolones were determined with quinolone-susceptible Staphylococcus aureus RN4220 by a direct plating method. First-step mutants were selected less frequently with trovafloxacin (1.1 x 10(-10) at 2 to 4x the MIC) than with levofloxacin or ciprofloxacin (3.0 x 10(-7) to 3.0 x 10(-8) at 2 to 4x the MIC). Mutants with a change in GrlA (Ser80-->Phe or Tyr) were most commonly selected with trovafloxacin, ciprofloxacin, levofloxacin, or pefloxacin. First-step mutants were difficult to select with sparfloxacin; however, second-step mutants with mutations in gyrA were easily selected when a preexisting mutation in grlA was present. Against 29 S. aureus clinical isolates with known mutations in gyrA and/or grlA, trovafloxacin was the most active quinolone tested (MIC at which 50% of isolates are inhibited [MIC(50)] and MIC(90), 1 and 4 microg/ml, respectively); in comparison, MIC(50)s and MIC(90)s were 32 and 128, 16 and 32, 8 and 32, and 128 and 256 microg/ml for ciprofloxacin, sparfloxacin, levofloxacin, and pefloxacin, respectively. Strains with a mutation in grlA only were generally susceptible to all of the quinolones tested. For mutants with changes in both grlA and gyrA MICs were higher and were generally above the susceptibility breakpoint for ciprofloxacin, sparfloxacin, levofloxacin, and pefloxacin. Addition of reserpine (20 microg/ml) lowered the MICs only of ciprofloxacin fourfold or more for 18 of 29 clinical strains. Topoisomerase IV and DNA gyrase genes were cloned from S. aureus RN4220 and from two mutants with changes in GrlA (Ser80-->Phe and Glu84-->Lys). The enzymes were overexpressed in Escherichia coli GI724, purified, and used in DNA catalytic and cleavage assays that measured the relative potency of each quinolone. Trovafloxacin was at least five times more potent than ciprofloxacin, sparfloxacin, levofloxacin, or pefloxacin in stimulating topoisomerase IV-mediated DNA cleavage. While all of the quinolones were less potent in cleavage assays with the altered topoisomerase IV, trovafloxacin retained its greater potency relative to those of the other quinolones tested. The greater intrinsic potency of trovafloxacin against the lethal topoisomerase IV target in S. aureus contributes to its improved potency against clinical strains of S. aureus that are resistant to other quinolones.     

In vitro activity of DC-159a, a new broad-spectrum fluoroquinolone, compared with that of other agents against drug-susceptible and -resistant pneumococci

DC-159a yielded MICs of or=4 microg/ml). Although the MICs for DC-159a against quinolone-susceptible pneumococci were a few dilutions higher than those of gemifloxacin, the MICs of these two compounds against 28 quinolone-resistant pneumococci were identical. The DC-159a MICs against quinolone-resistant strains did not appear to depend on the number or the type of mutations in the quinolone resistance-determining region. DC-159a, as well as the other quinolones tested, was bactericidal after 24 h at 2x MIC against 11 of 12 strains tested. Two of the strains were additionally tested at 1 and 2 h, and DC-159a at 4x MIC showed significant killing as early as 2 h. Multistep resistance selection studies showed that even after 50 consecutive subcultures of 10 strains in the presence of sub-MICs, DC-159a produced only two mutants with maximum MICs of 1 microg/ml.     

In vitro selection of resistance in haemophilus influenzae by 4 quinolones and 5 beta-lactams

We tested abilities of ciprofloxacin, levofloxacin, gatifloxacin, moxifloxacin, amoxicillin, amoxicillin/clavulanate, cefixime, cefpodoxime, and cefdinir to select resistant mutants in 5 beta-lactamase positive and 5 beta-lactamase negative Haemophilus influenzae strains by single and multistep methodology. In multistep tests, amoxicillin, amoxicillin/clavulanate and cefpodoxime exposure did not cause >4-fold minimum inhibitory concentration (MIC) increase after 50 days. One mutant selected by cefdinir had one amino acid substitution (Gly490Glu) in PBP3 and became resistant to cefdinir. Cefixime exposure caused 8-fold MIC-increase in 1 strain with TEM but the mutant remained cefixime susceptible and had no alteration in PBP3 or TEM. Among 10 strains tested, ciprofloxacin, moxifloxacin, gatifloxacin, levofloxacin caused >4-fold MIC increase in 6, 6, 5, and 2 strain, respectively. Despite the increases in quinolone MICs, none of the mutants became resistant to quinolones by established criteria. Quinolone selected mutants had quindone resistance-determining region (QRDR) alterations in GyrA, GyrB, ParC, ParE. Four quinolone mutants had no QRDR alterations. Among beta-lactams cefdinir and cefixime selected one mutant each with higher MICs however amoxicillin, amoxicillin/clavulanate, and cefpodoxime exposure did not select resistant mutants.     

Selection of quinolone resistance in Streptococcus pneumoniae exposed in vitro to subinhibitory drug concentrations

OBJECTIVES: Does exposure to subinhibitory concentrations of quinolones favour overexpression of efflux pumps or selection of target site mutations? METHODS: ATCC 49,619 (fully susceptible) and SP32 (clinical isolate with PmrA-mediated efflux and mutation in ParE) were exposed for 24 h in broth to ciprofloxacin, levofloxacin, moxifloxacin or garenoxacin at concentrations of 0.5x the MIC, with daily re-adjustments for up to 13 days. Efflux was detected phenotypically (decrease in MIC in the presence of reserpine), and expression of pmrA and patA/patB was measured by real-time PCR and comparative RT-PCR, respectively. Target site mutations were detected by sequencing of the quinolone resistance determining regions in parC, parE and gyrA. The clonal identity of isolates was checked by PFGE of genomic DNA. RESULTS: Ciprofloxacin selected for stable mutants with 2.5-5-fold MIC increases for ciprofloxacin, 2-3-fold for levofloxacin and 1.3-2-fold for garenoxacin and moxifloxacin [partial reversion with reserpine for ciprofloxacin, gemifloxacin and levofloxacin (SP32 strain only), but not for garenoxacin and moxifloxacin]. Increased MICs were associated with overexpression of patA/B but not pmrA. In contrast, exposure to levofloxacin, moxifloxacin or garenoxacin selected target site mutations (gyrA, parC, parE) in both strains. Increases in MIC caused by efflux were similar to those caused by target site mutations. CONCLUSIONS: Exposure of Streptococcus pneumoniae to subinhibitory MICs of ciprofloxacin, a substrate for efflux pumps, results in patA/B-mediated efflux whatever the initial level of expression of pmrA of the strain. Quinolones that are poorly (levofloxacin) or not affected (moxifloxacin, garenoxacin) in their activity by efflux transporters preferentially select for target site mutants.     

In vitro antibacterial activity of fluoroquinolones against Porphyromonas gingivalis strains

OBJECTIVES: The objective of the study was to evaluate the in vitro activity of ciprofloxacin, gatifloxacin and moxifloxacin against 16 Porphyromonas gingivalis strains. METHODS: MICs of the quinolones were established by Etest and the agar dilution technique. Experiments focused on determination of the spontaneous mutation rate and the induction of resistant strains, using 0.25-fold MIC of antibiotic. Fragments of gyrA and gyrB as well as of parC were sequenced. RESULTS: Moxifloxacin and gatifloxacin had very low MIC values. Subinhibitory concentrations of the fluoroquinolones rapidly induced mutations. The spontaneous mutation rate was strain- and quinolone-dependent; the lowest rate was encountered after moxifloxacin. The predicted serum concentrations of the quinolones were bactericidal to wild-type strains, but 100 mg/L of each tested quinolone was insufficient to kill a mutant exhibiting moderate resistance. Often the mutants exhibited high resistance to >/=32 mg/L. All these mutants bore a Ser-83-->Phe substitution in GyrA. CONCLUSIONS: DNA gyrase is the primary target of fluoroquinolones in P. gingivalis. In terms of the achievable level in the gingival fluid and the MICs, moxifloxacin might prevent the development of resistance and may be an alternative in the antibiotic treatment of P. gingivalis-associated periodontitis.     

In vitro activity of the new quinolone WCK 771 against staphylococci

The activity of WCK 771, an experimental quinolone developed to overcome quinolone resistance in staphylococci and other bacteria, was determined against quinolone-susceptible and -resistant Staphylococcus aureus and S. epidermidis. WCK 771 MICs for 50 and 90% of the strains tested (MIC(50) and MIC(90), respectively) were 0.008 and 0.015 microg/ml for S. aureus (n = 43) and 0.015 and 0.03 microg/ml for S. epidermidis (n = 44) for quinolone-susceptible isolates, compared to ciprofloxacin values of 0.12 and 0.25 microg/ml and 0.25 and 0.5 microg/ml, respectively. Values for levofloxacin were 0.12 and 0.25 microg/ml and 0.12 and 0.25 microg/ml, those for clinafloxacin were 0.015 and 0.03 microg/ml and 0.015 and 0.03 microg/ml, those for moxifloxacin were 0.03 and 0.06 microg/ml and 0.06 and 0.12 microg/ml, and those for gatifloxacin were 0.06 and 0.12 microg/ml and 0.12 and 0.25 microg/ml, respectively. The WCK 771 MIC(50) and MIC(90), respectively, were 0.5 and 1 microg/ml for both species of staphylococci (n = 73 for S. aureus, n = 70 for S. epidermidis) for isolates highly resistant to ciprofloxacin (MIC(50) and MIC(90), >32 and >32 microg/ml, respectively). Values for levofloxacin were 8 and 32 microg/ml and 8 and 32 microg/ml, those for clinafloxacin were 1 and 2 microg/ml and 0.5 and 2 microg/ml, those for moxifloxacin 4 and >4 microg/ml and 4 and >4 microg/ml, and those for gatifloxacin were 4 and >4 microg/ml and 2 and >4 microg/ml, respectively. WCK 771 and clinafloxacin demonstrated MICs of 1 microg/ml against three vancomycin-intermediate strains. WCK 771 showed concentration-independent killing for up to 24 h at 2, 4, and 8 times the MICs against quinolone-resistant staphylococci and was also bactericidal after 8 h for high-density inocula (10(8) CFU/ml) of quinolone-resistant strains at 5 microg/ml, whereas moxifloxacin at 7.5 microg/ml was bacteriostatic. WCK 771 was not a substrate of the NorA efflux pump as evident from the similar MICs against both an efflux-positive and an efflux-negative strain. Overall, WCK 771 was the most potent quinolone tested against the staphylococci tested, regardless of quinolone susceptibility.     

Development and mechanism of fluoroquinolone resistance in Legionella pneumophila

The potential for selection in vitro of Legionella pneumophila mutants resistant to fluoroquinolones was investigated. Six distinct clinical isolates of L. pneumophila were subcultured in subinhibitory concentrations of ciprofloxacin, levofloxacin, clinafloxacin, trovafloxacin and moxifloxacin until MICs increased at least eight-fold. The numbers of serial passages required in microbroth dilution series were determined. The gyrA gene of the six parental strains, and 12 selected mutant strains, was sequenced. The five quinolones differed markedly in their ability to select mutants with decreased susceptibility. The average number of serial passages required was low in the cases of clinafloxacin (n = 10.6), ciprofloxacin and levofloxacin (both n = 13), but notably higher for trovafloxacin (n = 26.6) and moxifloxacin (n = 22.5). Five mutants treated with ciprofloxacin and three treated with moxifloxacin showed Thr83-->Lys or Thr83-->Ile amino acid changes in the gyrA gene. In conclusion, different quinolones lose their antimicrobial effect after a varying number of passages. This study demonstrated, for the first time to our knowledge, that gyrA in L. pneumophila is a possible target of fluoroquinolones.     

Antipneumococcal activities of gemifloxacin compared to those of nine other agents

The activities of gemifloxacin compared to those of nine other agents was tested against a range of penicillin-susceptible and -resistant pneumococci by agar dilution, microdilution, time-kill, and post-antibiotic effect (PAE) methods. Against 64 penicillin-susceptible, 68 penicillin-intermediate, and 75 penicillin-resistant pneumococci (all quinolone susceptible), agar dilution MIC(50)s (MICs at which 50% of isolates are inhibited)/MIC(90)s (in micrograms per milliliter) were as follows: gemifloxacin, 0.03/0.06; ciprofloxacin, 1.0/4.0; levofloxacin, 1.0/2. 0; sparfloxacin, 0.5/1.0; grepafloxacin, 0.125/0.5; trovafloxacin, 0. 125/0.25; amoxicillin, 0.016/0.06 (penicillin-susceptible isolates), 0.125/1.0 (penicillin-intermediate isolates), and 2.0/4.0 (penicillin-resistant isolates); cefuroxime, 0.03/0.25 (penicillin-susceptible isolates), 0.5/2.0 (penicillin-intermediate isolates), and 8.0/16.0 (penicillin-resistant isolates); azithromycin, 0.125/0.5 (penicillin-susceptible isolates), 0. 125/>128.0 (penicillin-intermediate isolates), and 4.0/>128.0 (penicillin-resistant isolates); and clarithromycin, 0.03/0.06 (penicillin-susceptible isolates), 0.03/32.0 (penicillin-intermediate isolates), and 2.0/>128.0 (penicillin-resistant isolates). Against 28 strains with ciprofloxacin MICs of >/=8 microg/ml, gemifloxacin had the lowest MICs (0.03 to 1.0 microg/ml; MIC(90), 0.5 microg/ml), compared with MICs ranging between 0.25 and >32.0 microg/ml (MIC(90)s of 4.0 to >32.0 microg/ml) for other quinolones. Resistance in these 28 strains was associated with mutations in parC, gyrA, parE, and/or gyrB or efflux, with some strains having multiple resistance mechanisms. For 12 penicillin-susceptible and -resistant pneumococcal strains (2 quinolone resistant), time-kill results showed that levofloxacin at the MIC, gemifloxacin and sparfloxacin at two times the MIC, and ciprofloxacin, grepafloxacin, and trovafloxacin at four times the MIC were bactericidal for all strains after 24 h. Gemifloxacin was uniformly bactericidal after 24 h at 相似文献   

Phenotypic characterization of quinolone-resistant mutants of Enterobacteriaceae selected from wild type, gyrA type and multiply-resistant (marA) type strains.

The NCTC type strains of Escherichia coli, Enterobacter cloacae, Serratia marcescens and Klebsiella pneumoniae were exposed to 3, 5 and 10 x MIC of nalidixic acid, enoxacin, ciprofloxacin, PD 117596 and PD 127391. From each strain a mutant with a high MIC of quinolones alone (gyrA) and a mutant with intermediate resistance to quinolones, some beta-lactams, chloramphenicol and tetracycline (multiply resistant, m-r) were selected on agar containing antibiotics. The gyrA mutants required a higher concentration of quinolone to inhibit DNA synthesis by 50% but quinolone uptake kinetics and outer membrane profile were the same as the wild type. The m-r mutants had similar DNA synthesis IC50 as the wild type, decreased quinolone uptake kinetics and had decreased expression of an OMP of approximately 40 kD. The gyrA and m-r mutants were then exposed to 3, 5 and 10 x MIC of the same quinolones and new mutants (F2) selected. The F2 mutants from the gyrA mutants displayed a further increase in quinolone MIC; the F2 mutants from the m-r mutants had several phenotypes: high quinolone MICs with cross resistance to other agents, high quinolone resistance alone, or intermediate quinolone resistance alone. Most F2 mutants had MICs above the recommended breakpoint concentrations for quinolones. The F2 mutants often had altered biochemical profiles (API 20E), however, only in the case of E. cloacae did this affect speciation with the strains being identified as Rhanella aquatalis.     

Activity of BMS284756 against 2,681 recent clinical isolates of Haemophilus influenzae and Moraxella catarrhalis: Report from The SENTRY Antimicrobial Surveillance Program (2000) in Europe, Canada and the United States

Although the isolation and detection of fluoroquinolone-resistant Haemophilus influenzae and Moraxella catarrhalis has been a very rare occurrence, newer agents in the quinolone class must be evaluated to determine their comparative potencies and to develop in vitro testing methods. BMS284756 is an investigational desfluoro(6)-quinolone with a spectrum of activity most similar to recently introduced agents such as gatifloxacin and trovafloxacin. This compound was compared to levofloxacin, gatifloxacin, ciprofloxacin and moxifloxacin, as well as other orally administered antimicrobials against 1,872 H. influenzae and 810 M. catarrhalis isolates. Two Canadian H. influenzae strains had ciprofloxacin MICs elevated above the normal wild type susceptible MIC population (> 0.06 microg/mL). All other strains of H. influenzae and M catarrhalis were highly susceptible to the tested quinolones (MIC(90,) < or = 0.016 or 0.03 microg/mL). For the two H. influenzae isolates with elevated quinolone MICs the potency rank order was: gatifloxacin and BMS284756 (MICs, 0.25 and 1 microg/mL) > levofloxacin and moxifloxacin > ciprofloxacin (MICs, 0.5 and > 2 microg/mL). The comparison of Etest (AB BIODISK, Solna, Sweden) and disk diffusion results to the reference broth microdilution values produced acceptable intermethod accuracy when applied to BMS284756. This novel desfluoro compound possesses promising activity against fastidious Gram-negative respiratory tract pathogens and further clinical development is underway.     

In vitro development of resistance to DX-619 and other quinolones in enterococci

OBJECTIVES: To investigate the molecular events involved in the development of quinolone resistance in enterococci. METHODS: Clinical isolates of Enterococcus faecium and Enterococcus faecalis were exposed to inhibitory and subinhibitory concentrations of DX-619, ciprofloxacin, levofloxacin, gatifloxacin and moxifloxacin. Mutational frequencies were calculated and susceptibility changes were determined. The quinolone resistance determining regions (QRDRs) of gyrA and parC in less-susceptible mutants were amplified by PCR and sequenced. RESULTS: Single-step mutants of E. faecalis and E. faecium were selected with all drugs. There were no differences in the frequencies of mutant selection among drugs, with frequencies ranging from 10(-5) to 10(-8). All single-step mutants were inhibited by 0.03-1 mg/L DX-619, 0.25-8 mg/L moxifloxacin, 0.5-8 mg/L gatifloxacin, 1-16 mg/L levofloxacin and 1-32 mg/L ciprofloxacin. No QRDR changes were observed in single-step mutants. Less-susceptible mutants selected after five passages on agar containing subinhibitory quinolone concentrations were inhibited by 0.12-8 mg/L DX-619, 1-64 mg/L moxifloxacin, 2-64 mg/L gatifloxacin and 2-128 mg/L levofloxacin and ciprofloxacin. QRDR changes were detected in only 9 of the 20 fifth-passage mutants, suggesting that mutations outside the purported QRDRs and/or other resistance mechanisms were also involved. CONCLUSION: The relatively high frequencies at which single-step mutants were selected with all drugs indicate that caution is necessary if quinolones are to be considered for monotherapy of serious enterococcal infections. DX-619, the most potent quinolone, may have potential as an anti-enterococcal agent if sufficient concentrations can be safely attained in vivo.     

In vitro activities of garenoxacin (BMS-284756) against Haemophilus influenzae isolates with different fluoroquinolone susceptibilities

The in vitro activity of garenoxacin (BMS-284756) against 62 clinical Haemophilus influenzae isolates with different fluoroquinolone susceptibilities was determined by the microdilution susceptibility testing method and compared with the activities of other oral quinolones and nonquinolone oral antimicrobial agents. Cefixime presented the highest intrinsic activity (MIC at which 50% of the isolates tested were inhibited [MIC(50)], 0.01 microg/ml), followed by garenoxacin, moxifloxacin, and ciprofloxacin (MIC(50), 0.06 microg/ml), levofloxacin (MIC(50), 0.12 microg/ml), cefuroxime (MIC(50), 1.0 microg/ml), and amoxicillin-clavulanate (MIC(50), 1.0/0.5 microg/ml), amoxicillin (MIC(50), 2 microg/ml), azithromycin (MIC(50), 4 microg/ml), and erythromycin (MIC(50), 8 microg/ml). In strains with ciprofloxacin MICs of < or =0.06 microg/ml, ciprofloxacin and garenoxacin displayed similar MIC(50)s and MIC(90)s, one dilution lower than those of moxifloxacin and levofloxacin. For strains for which ciprofloxacin MICs were > or = 0.12 microg/ml, MIC(50)s were similar for the four quinolones tested, although garenoxacin presented the widest activity range (0.03 to 32 microg/ml) and the highest MIC at which 90% of the isolates tested were inhibited (16.0 microg/ml). For strains without amino acid changes in the quinolone resistance determining region (QRDR) of GyrA and ParC, garenoxacin MICs were < or =0.03 microg/ml; with a single amino acid change in GyrA, garenoxacin MICs were 0.06 to 0.12 microg/ml; with one amino acid change each in GyrA and ParC, garenoxacin MICs were 0.5 to 2.0 micro g/ml; one amino acid change in ParC combined with two amino acid changes in GyrA increased the MICs to > or = 4 microg/ml for all assayed quinolones. We conclude that garenoxacin has excellent activity against H. influenzae, although progressive acquired resistance was observed by step-by-step mutation in the QRDR of gyrA and parC.     

Activities of clinafloxacin, gatifloxacin, gemifloxacin, and trovafloxacin against recent clinical isolates of levofloxacin-resistant Streptococcus pneumoniae

The activities of two investigational fluoroquinolones and three fluoroquinolones that are currently marketed were determined for 182 clinical isolates of Streptococcus pneumoniae. The collection included 57 pneumococcal isolates resistant to levofloxacin (MIC >/= 8 microg/ml) recovered from patients in North America and Europe. All isolates were tested with clinafloxacin, gatifloxacin, gemifloxacin, levofloxacin, and trovafloxacin by the National Committee for Clinical Laboratory Standards broth microdilution and disk diffusion susceptibility test methods. Gemifloxacin demonstrated the greatest activity on a per gram basis, followed by clinafloxacin, trovafloxacin, gatifloxacin, and levofloxacin. Scatterplots of the MICs and disk diffusion zone sizes revealed a well-defined separation of levofloxacin-resistant and -susceptible strains when the isolates were tested against clinafloxacin and gatifloxacin. DNA sequence analyses of the quinolone resistance-determining regions of gyrA, gyrB, parC, and parE from 21 of the levofloxacin-resistant strains identified eight different patterns of amino acid changes. Mutations among the four loci had the least effect on the MICs of gemifloxacin and clinafloxacin, while the MICs of gatifloxacin and trovafloxacin increased by up to six doubling dilutions. These data indicate that the newer fluoroquinolones have greater activities than levofloxacin against pneumococci with mutations in the DNA gyrase or topoisomerase IV genes. Depending upon pharmacokinetics and safety, the greater potency of these agents could provide improved clinical efficacy against levofloxacin-resistant pneumococcal strains.     

Inhibitory activities of quinolones against DNA gyrase and topoisomerase IV of Enterococcus faecalis

We have cloned the DNA gyrase and topoisomerase IV genes of Enterococcus faecalis to examine the actions of quinolones against E. faecalis genetically and enzymatically. We first generated levofloxacin-resistant mutants of E. faecalis by stepwise selection with increasing drug concentrations and analyzed the quinolone resistance-determining regions of gyrA and parC from the resistant mutants. Isogenic mutants with low-level resistance contained a mutation in gyrA, whereas those with higher levels of resistance had mutations in both gyrA and parC. These results suggested that gyrA is the primary target for levofloxacin in E. faecalis. We then purified the recombinant DNA gyrase and topoisomerase IV enzymes of E. faecalis and measured the in vitro inhibitory activities of quinolones against these enzymes. The 50% inhibitory concentrations (IC(50)s) of levofloxacin, ciprofloxacin, sparfloxacin, tosufloxacin, and gatifloxacin for DNA gyrase were found to be higher than those for topoisomerase IV. In conflict with the genetic data, these results indicated that topoisomerase IV would be the primary target for quinolones in E. faecalis. Among the quinolones tested, the IC(50) of sitafloxacin (DU-6859a), which shows the greatest potency against enterococci, for DNA gyrase was almost equal to that for topoisomerase IV; its IC(50)s were the lowest among those of all the quinolones tested. These results indicated that other factors can modulate the effect of target affinity to determine the bacterial killing pathway, but the highest inhibitory actions against both enzymes correlated with good antienterococcal activities.     

Activities and postantibiotic effects of gemifloxacin compared to those of 11 other agents against Haemophilus influenzae and Moraxella catarrhalis

The activity of gemifloxacin against Haemophilus influenzae and Moraxella catarrhalis was compared to those of 11 other agents. All quinolones were very active (MICs, 相似文献   

Antipneumococcal Activity of BMS 284756 Compared to Those of Six Other Agents

Antipneumococcal activity of BMS 284756 was compared to those of six agents by MIC and time-kill methodologies. BMS 284756 had the lowest MICs compared to those of ciprofloxacin, levofloxacin, and moxifloxacin against quinolone-susceptible (< or =0.016 to 0.06 microg/ml) and quinolone-resistant (0.03 to 1 microg/ml) pneumococci. BMS 284756 was bactericidal against 11 of 12 strains at two times the MIC after 24 h.