scholarly journals Enrichment of Fluoroquinolone-Resistant Staphylococcus aureus: Oscillating Ciprofloxacin Concentrations Simulated at the Upper and Lower Portions of the Mutant Selection Window

2008 ◽  
Vol 52 (6) ◽  
pp. 1924-1928 ◽  
Author(s):  
Alexander A. Firsov ◽  
Irene Y. Lubenko ◽  
Maria V. Smirnova ◽  
Elena N. Strukova ◽  
Stephen H. Zinner
Keyword(s):  
Staphylococcus Aureus ◽  
Dependent Manner ◽  
Time Curve ◽  
Mutant Selection ◽  
Selection Window ◽  
Lower Case ◽  
Mutant Prevention Concentration ◽  
Kill Curve ◽  
Time Kill ◽  
Selection Of

ABSTRACT The time inside the mutant selection window (MSW), T MSW, appears to be less predictive of the selection of fluoroquinolone-resistant Staphylococcus aureus than is the ratio of the area under the concentration-time curve (AUC) to the MIC. This observation might be attributed to the fact that T MSW does not consider the actual position of simulated antibiotic concentrations inside the MSW, which also might influence the amplification of resistant mutants. To test this hypothesis, the enrichment of ciprofloxacin-resistant S. aureus was studied at ciprofloxacin (CIP) concentrations that oscillate near the mutant prevention concentration (MPC), i.e., closer to the top of the MSW (“upper case”), and closer to the MIC, i.e., at the lower limit of the MSW (“lower case”) at the same T MSW. Two methicillin-resistant strains of S. aureus, ATCC 6538 and ATCC 43300 (MICs of 0.25 and 0.5 mg/liter, respectively, and MPCs of 4 and 2 mg/liter, respectively), were exposed to twice-daily CIP treatments for three consecutive days. With S. aureus ATCC 6538, the simulated ratios of the AUC at 24 h (AUC24) to the MIC were 50 and 260 h (T MSW 75% of the dosing interval). With S. aureus ATCC 43300, the simulated AUC24/MICs were 30 and 100 h (T MSW 56%). With each organism, mutants resistant to CIP were enriched in an AUC24/MIC-dependent manner: the higher the AUC24/MIC ratio, the lower the growth on CIP-containing plates. For example, the area under the time-kill curve of mutants resistant to 4× MIC of CIP in the upper case was three times smaller than that in the lower case for both S. aureus strains. Similar differences were seen at the higher (8× MIC) and lower (2× MIC) CIP concentrations. These data highlight differences in the selection of resistant S. aureus, depending on the position of simulated concentrations inside the MSW at a given T MSW. This explains why T MSW-based predictions of resistance are less accurate than those based on AUC/MIC and AUC/MPC.

Susceptibility and PK/PD relationships of Staphylococcus aureus strains isolated from the milk of sheep and goats with clinical mastitis to five veterinary fluoroquinolones

2017 ◽  
Vol 180 (15) ◽  
pp. 376-376 ◽  
Author(s):  
J. M. Serrano-Rodríguez ◽  
C. Cárceles-García ◽  
C. M. Cárceles-Rodríguez ◽  
M. L. Gabarda ◽  
J. M. Serrano-Caballero ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Inhibitory Concentration ◽  
Clinical Mastitis ◽  
The Other ◽  
Mutant Selection ◽  
Sheep And Goats ◽  
Selection Window ◽  
Mutant Prevention Concentration ◽  
Higher Doses ◽  
Selection Of

Minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) of veterinary fluoroquinolones as enrofloxacin, its metabolite ciprofloxacin, danofloxacin, difloxacin and marbofloxacin against Staphylococcus aureus strains (n=24) isolated from milk of sheep and goats affected by clinical mastitis were evaluated. The authors have used the MIC and MPC, as well as the pharmacokinetic-pharmacodynamic relationships in plasma and milk. MIC values were significantly different between drugs, unlike MPC values. Lower MIC values were obtained for danofloxacin and difloxacin, middle and higher values for enrofloxacin, ciprofloxacin and marbofloxacin. However, differences in MPC values were not found between drugs. At conventional doses, the AUC24/MIC and AUC24/MPC ratios were close to 30–80 hours and 5–30 hours, with exception of danofloxacin, in plasma and milk. The time inside the mutant selection window (TMSW) was close to 3–6 hours for enrofloxacin, ciprofloxacin and marbofloxacin, near to 8 hours for danofloxacin and 12–22 hours for difloxacin. From these data, the mutant selection window could be higher for danofloxacin and difloxacin compared with the other fluoroquinolones tested. The authors concluded that enrofloxacin and marbofloxacin, at conventional doses, could prevent the selection of bacterial subpopulations of S aureus, unlike danofloxacin and difloxacin, where higher doses could be used.

scholarly journals Synergistic Combination of Linezolid and Fosfomycin Closing Each Other’s Mutant Selection Window to Prevent Enterococcal Resistance

2021 ◽  
Vol 11 ◽  
Author(s):  
Lifang Jiang ◽  
Na Xie ◽  
Mingtao Chen ◽  
Yanyan Liu ◽  
Shuaishuai Wang ◽  
...  
Keyword(s):  
Ribosomal Proteins ◽  
Bacterial Resistance ◽  
Selection Index ◽  
Resistance Mechanism ◽  
Mutant Selection ◽  
Selection Window ◽  
Mutant Prevention Concentration ◽  
Resistant Mutants ◽  
Synergistic Combination ◽  
Selection Of

Enterococci, the main pathogens associated with nosocomial infections, are resistant to many common antibacterial drugs including β-lactams, aminoglycosides, etc. Combination therapy is considered an effective way to prevent bacterial resistance. Preliminary studies in our group have shown that linezolid combined with fosfomycin has synergistic or additive antibacterial activity against enterococci, while the ability of the combination to prevent resistance remains unknown. In this study, we determined mutant prevention concentration (MPC) and mutant selection window (MSW) of linezolid, fosfomycin alone and in combination including different proportions for five clinical isolates of Enterococcus and characterized the resistance mechanism for resistant mutants. The results indicated that different proportions of linezolid combined with fosfomycin had presented different MPCs and MSWs. Compared with linezolid or fosfomycin alone, the combination can restrict the enrichment of resistant mutants at a lower concentration. A rough positive correlation between the selection index (SI) of the two agents in combination and the fractional inhibitory concentration index (FICI) of the combination displayed that the smaller FICI of linezolid and fosfomycin, the more probable their MSWs were to close each other. Mutations in ribosomal proteins (L3 and L4) were the mechanisms for linezolid resistant mutants. Among the fosfomycin-resistant mutants, only two strains have detected the MurA gene mutation related to fosfomycin resistance. In conclusion, the synergistic combination of linezolid and fosfomycin closing each other’s MSW could effectively suppress the selection of enterococcus resistant mutants, suggesting that the combination may be an alternative for preventing enterococcal resistance. In this study, the resistance mechanism of fosfomycin remains to be further studied.

scholarly journals Searching for the Optimal Predictor of Ciprofloxacin Resistance in Klebsiella pneumoniae by UsingIn VitroDynamic Models

2015 ◽  
Vol 60 (3) ◽  
pp. 1208-1215 ◽  
Author(s):  
Elena N. Strukova ◽  
Yury A. Portnoy ◽  
Andrey V. Romanov ◽  
Mikhail V. Edelstein ◽  
Stephen H. Zinner ◽  
...  
Keyword(s):  
Klebsiella Pneumoniae ◽  
Area Under The Curve ◽  
Mutant Selection ◽  
Content Type ◽  
Selection Window ◽  
Mutant Prevention Concentration ◽  
Ciprofloxacin Resistance ◽  
Resistant Mutants ◽  
Time Courses ◽  
Selection Of

There is growing evidence of applicability of the hypothesis of the mutant selection window (MSW), i.e., the range between the MIC and the mutant prevention concentration (MPC), within which the enrichment of resistant mutants is most probable. However, it is not clear if MPC-based pharmacokinetic variables are preferable to the respective MIC-based variables as interstrain predictors of resistance. To examine the predictive power of the ratios of the area under the curve (AUC24) to the MPC and to the MIC, the selection of ciprofloxacin-resistant mutants of threeKlebsiella pneumoniaestrains with different MPC/MIC ratios was studied. Each organism was exposed to twice-daily ciprofloxacin for 3 days at AUC24/MIC ratios that provide peak antibiotic concentrations close to the MIC, between the MIC and the MPC, and above the MPC. ResistantK. pneumoniaemutants were intensively enriched at an AUC24/MIC ratio of 60 to 360 h (AUC24/MPC ratio from 2.5 to 15 h) but not at the lower or higher AUC24/MIC and AUC24/MPC ratios, in accordance with the MSW hypothesis. AUC24/MPC and AUC24/MIC relationships with areas under the time courses of ciprofloxacin-resistantK. pneumoniae(AUBCM) were bell shaped. These relationships predict highly variable “antimutant” AUC24/MPC ratios (20 to 290 h) compared to AUC24/MIC ratios (1,310 to 2,610 h). These findings suggest that the potential of the AUC24/MPC ratio as an interstrain predictor ofK. pneumoniaeresistance is lower than that of the AUC24/MIC ratio.

scholarly journals In Vitro Resistance Selection in Shigella flexneri by Azithromycin, Ceftriaxone, Ciprofloxacin, Levofloxacin, and Moxifloxacin

2017 ◽  
Vol 61 (7) ◽  
Author(s):  
George P. Allen ◽  
Kayla A. Harris
Keyword(s):  
Shigella Flexneri ◽  
Dosage Interval ◽  
Time Curve ◽  
Mutant Selection ◽  
Content Type ◽  
Selective Enrichment ◽  
Mutant Prevention Concentration ◽  
Time Kill

ABSTRACT Shigella flexneri continues to be a major cause of diarrhea-associated illness, and increasing resistance to first-line antimicrobials complicates the treatment of infections caused by this pathogen. We investigated the pharmacodynamics of current antimicrobial treatments for shigellosis to determine the likelihood of resistance promotion with continued global antimicrobial use. The mutant prevention concentration (MPC) and mutant selection window (MSW) were determined for azithromycin, ceftriaxone, ciprofloxacin, levofloxacin, and moxifloxacin against a wild-type strain of S. flexneri (ATCC 12022) and an isogenic gyrA mutant (m-12022). Time-kill assays were performed to determine antimicrobial killing. Concentrations of approved doses of ciprofloxacin, levofloxacin, and moxifloxacin are predicted to surpass the MPC for a majority of the dosage interval against ATCC 12022. However, against m-12022, concentrations of all fluoroquinolones are predicted to fall below the MPC and remain in the MSW for a majority of the dosage interval. Concentrations of ceftriaxone fall within the MSW for the majority of the dosage interval for both strains. All agents other than azithromycin displayed bactericidal activity in time-kill assays. Results of pharmacodynamic analyses suggest that all tested fluoroquinolones would achieve a favorable area under the concentration-time curve (AUC)/MPC ratio for ATCC 12022 and would restrict selective enrichment of mutants but that mutant selection in m-12022 would be likely if ciprofloxacin were used. Based on pharmacodynamic analyses, azithromycin and ceftriaxone are predicted to promote mutant selection in both strains. Confirmation of these findings and examination of novel treatment regimens using in vivo studies are warranted.

scholarly journals Mutant Prevention Concentration of Garenoxacin (BMS-284756) for Ciprofloxacin-Susceptible or -Resistant Staphylococcus aureus

2003 ◽  
Vol 47 (3) ◽  
pp. 1023-1027 ◽  
Author(s):  
Xilin Zhao ◽  
William Eisner ◽  
Nathan Perl-Rosenthal ◽  
Barry Kreiswirth ◽  
Karl Drlica
Keyword(s):  
Staphylococcus Aureus ◽  
Treatment Time ◽  
Mutant Selection ◽  
Selective Enrichment ◽  
Drug Concentrations ◽  
Selection Window ◽  
Mutant Prevention Concentration ◽  
Resistant Mutants

ABSTRACT The new quinolone garenoxacin (BMS-284756), which lacks a C-6 fluorine, was examined for its ability to block the growth of Staphylococcus aureus. Measurement of the MIC and the mutant prevention concentration (MPC) revealed that garenoxacin was 20-fold more potent than ciprofloxacin for a variety of ciprofloxacin-susceptible isolates, some of which were resistant to methicillin. The MPC for 90% of the isolates (MPC90) was below published serum drug concentrations achieved with recommended doses of garenoxacin. These in vitro observations suggest that garenoxacin has a low propensity for selective enrichment of fluoroquinolone-resistant mutants among ciprofloxacin-susceptible isolates of S. aureus. For ciprofloxacin-resistant isolates, the MIC at which 90% of the isolates tested were inhibited was below serum drug concentrations while the MPC90 was not. Thus, for these strains, garenoxacin concentrations are expected to fall inside the mutant selection window (between the MIC and the MPC) for much of the treatment time. As a result, garenoxacin is expected to selectively enrich mutants with even lower susceptibility.

scholarly journals Pharmacodynamic Modeling of Ciprofloxacin Resistance in Staphylococcus aureus

2005 ◽  
Vol 49 (1) ◽  
pp. 209-219 ◽  
Author(s):  
Jeffrey J. Campion ◽  
Patrick J. McNamara ◽  
Martin E. Evans
Keyword(s):  
Staphylococcus Aureus ◽  
Resistance Mechanism ◽  
Viable Count ◽  
Pharmacodynamic Modeling ◽  
Mutant Selection ◽  
High Density Culture ◽  
Low Level ◽  
Selection Window ◽  
Mutant Prevention Concentration

ABSTRACT Three pharmacodynamic models of increasing complexity, designed for two subpopulations of bacteria with different susceptibilities, were developed to describe and predict the evolution of resistance to ciprofloxacin in Staphylococcus aureus by using pharmacokinetic, viable count, subpopulation, and resistance mechanism data obtained from in vitro system experiments. A two-population model with unique growth and killing rate constants for the ciprofloxacin-susceptible and -resistant subpopulations best described the initial killing and subsequent regrowth patterns observed. The model correctly described the enrichment of subpopulations with low-level resistance in the parent cultures but did not identify a relationship between the time ciprofloxacin concentrations were in the mutant selection window (the interval between the MIC and the mutant prevention concentration) and the enrichment of these subpopulations. The model confirmed the importance of resistant variants to the emergence of resistance by successfully predicting that resistant subpopulations would not emerge when a low-density culture, with a low probability of mutants, was exposed to a clinical dosing regimen or when a high-density culture, with a higher probability of mutants, was exposed to a transient high initial concentration designed to rapidly eradicate low-level resistant grlA mutants. The model, however, did not predict or explain the origin of variants with higher levels of resistance that appeared and became the predominant subpopulation during some experiments or the persistence of susceptible bacteria in other experiments where resistance did not emerge. Continued evaluation of the present two-population pharmacodynamic model and development of alternative models is warranted.

scholarly journals In VitroResistance Studies with Bacteria That Exhibit Low Mutation Frequencies: Prediction of “Antimutant” Linezolid Concentrations Using a Mixed Inoculum Containing both Susceptible and Resistant Staphylococcus aureus

2014 ◽  
Vol 59 (2) ◽  
pp. 1014-1019 ◽  
Author(s):  
Alexander A. Firsov ◽  
Maria V. Golikova ◽  
Elena N. Strukova ◽  
Yury A. Portnoy ◽  
Andrey V. Romanov ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Parent Strain ◽  
Bacterial Resistance ◽  
Dynamic Models ◽  
Time Curve ◽  
Mutant Selection ◽  
Content Type ◽  
Dosing Interval ◽  
Mixed Inoculum ◽  
Mutant Prevention Concentration

ABSTRACTBacterial resistance studies usingin vitrodynamic models are highly dependent on the starting inoculum that might or might not contain spontaneously resistant mutants (RMs). To delineate concentration-resistance relationships with linezolid-exposedStaphylococcus aureus, a mixed inoculum containing both susceptible cells and RMs was used. An RM selected after the 9th passage of the parent strain (MIC, 2 μg/ml) on antibiotic-containing media (RM9; MIC, 8 μg/ml) was chosen for the pharmacodynamic studies, because the mutant prevention concentration (MPC) of linezolid against the parent strain in the presence of RM9 at 102(but not at 104) CFU/ml did not differ from the MPC value determined in the absence of the RMs. Five-day treatments with twice-daily linezolid doses were simulated at concentrations either between the MIC and MPC or above the MPC.S. aureusRMs (resistant to 2× and 4× MIC but not 8× and 16× MIC) were enriched at ratios of the 24-h area under the concentration-time curve (AUC24) to the MIC that provide linezolid concentrations between the MIC and MPC for 100% (AUC24/MIC, 60 h) and 86% (AUC24/MIC, 120 h) of the dosing interval. No such enrichment occurred when linezolid concentrations were above the MIC and below the MPC for a shorter time (37% of the dosing interval; AUC24/MIC, 240 h) or when concentrations were consistently above the MPC (AUC24/MIC, 480 h). These findings obtained using linezolid-susceptible staphylococci supplemented with RMs support the mutant selection window hypothesis. This method provides an option to delineate antibiotic concentration-resistance relationships with bacteria that exhibit low mutation frequencies.

scholarly journals In Vivo Validation of the Mutant Selection Window Hypothesis with Moxifloxacin in a Murine Model of Tuberculosis

2007 ◽  
Vol 51 (12) ◽  
pp. 4261-4266 ◽  
Author(s):  
Deepak Almeida ◽  
Eric Nuermberger ◽  
Sandeep Tyagi ◽  
William R. Bishai ◽  
Jacques Grosset
Keyword(s):  
Drug Exposure ◽  
Serum Concentrations ◽  
Mutant Selection ◽  
Drug Concentrations ◽  
Selection Window ◽  
Mutant Prevention Concentration ◽  
Resistant Mutants ◽  
Selection Of

ABSTRACT Combination therapy is the most effective strategy to prevent emergence of resistance during tuberculosis (TB) treatment. Another strategy, albeit theoretical, is to limit the time that drug concentrations fall in the “mutant selection window” (MSW) between the MIC and the mutant prevention concentration (MPC). Drug concentrations above the MPC prevent selective amplification of resistant mutants in vitro even with a single drug exposure. The MSW concept has been validated using fluoroquinolones against Mycobacterium tuberculosis in vitro but not in vivo. Using a mouse model in which serum moxifloxacin (MXF) concentrations were maintained above the MPC, we tested whether this strategy prevents selection of MXF-resistant mutants. Beginning 2 weeks after aerosol infection with M. tuberculosis, when the mean lung log10 CFU count was 7.9 ± 0.2, mice received either no treatment or MXF in the diet at 0.25% to approximate the conventional human dose or 1.5% to maintain serum concentrations above the MPC (8 μg/ml). After 56 days of treatment, lung CFU counts were 3.5 ± 0.8 and 0.9 ± 0.6 in 0.25% and 1.5% of the MXF-treated mice, respectively. In mice given 0.25% MXF, MXF-resistant mutants were selected by day 28 and detected in 16% (3/19) of mice tested on day 56. No selection of MXF-resistant mutants was detected in mice given 1.5% MXF. We conclude that maintaining serum concentrations of MXF above the MPC prevents selection of MXF-resistant mutants. Although this target cannot be achieved clinically with MXF, it might be possible with new fluoroquinolones with more potent activity and/or improved pharmacokinetics.

scholarly journals Bacterial Resistance Studies UsingIn VitroDynamic Models: the Predictive Power of the Mutant Prevention and Minimum Inhibitory Antibiotic Concentrations

2013 ◽  
Vol 57 (10) ◽  
pp. 4956-4962 ◽  
Author(s):  
Alexander A. Firsov ◽  
Elena N. Strukova ◽  
Darya S. Shlykova ◽  
Yury A. Portnoy ◽  
Varvara K. Kozyreva ◽  
...  
Keyword(s):  
Predictive Power ◽  
Bacterial Resistance ◽  
Area Under The Curve ◽  
Mutant Selection ◽  
Content Type ◽  
E Coli ◽  
Selection Window ◽  
Mutant Prevention Concentration ◽  
Time Courses ◽  
Selection Of

ABSTRACTIn light of the concept of the mutant selection window, i.e., the range between the MIC and the mutant prevention concentration (MPC), MPC-related pharmacokinetic indices should be more predictive of bacterial resistance than the respective MIC-related indices. However, experimental evidence of this hypothesis remains limited and contradictory. To examine the predictive power of the ratios of the area under the curve (AUC24) to the MPC and the MIC, the selection of ciprofloxacin-resistant mutants of fourEscherichia colistrains with different MPC/MIC ratios was studied. Each organism was exposed to twice-daily ciprofloxacin for 3 days at AUC24/MIC ratios that provide peak antibiotic concentrations close to the MIC, between the MIC and the MPC, and above the MPC. ResistantE. coliwas intensively enriched at AUC24/MPCs from 1 to 10 h (AUC24/MIC from 60 to 360 h) but not at the lower or higher AUC24/MPC and AUC24/MIC ratios. AUC24/MPC and AUC24/MIC relationships of the areas under the time courses of ciprofloxacin-resistantE. coli(AUBCM) were bell-shaped. A Gaussian-like function fits the AUBCM-AUC24/MPC and AUBCM-AUC24/MIC data combined for all organisms (r2= 0.69 and 0.86, respectively). The predicted anti-mutant AUC24/MPC ratio was 58 ± 35 h, and the respective AUC24/MIC ratio was 1,080 ± 416 h. Although AUC24/MPC was less predictive of strain-independentE. coliresistance than AUC24/MIC, the established anti-mutant AUC24/MPC ratio was closer to values reported forStaphylococcus aureus(60 to 69 h) than the respective AUC24/MIC ratio (1,080 versus 200 to 240 h). This implies that AUC24/MPC might be a better interspecies predictor of bacterial resistance than AUC24/MIC.

scholarly journals In Vitro Pharmacodynamic Evaluation of the Mutant Selection Window Hypothesis Using Four Fluoroquinolones against Staphylococcus aureus

2003 ◽  
Vol 47 (5) ◽  
pp. 1604-1613 ◽  
Author(s):  
Alexander A. Firsov ◽  
Sergey N. Vostrov ◽  
Irene Y. Lubenko ◽  
Karl Drlica ◽  
Yury A. Portnoy ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Half Life ◽  
Dynamic Models ◽  
Daily Administration ◽  
Human Pharmacokinetics ◽  
Mutant Selection ◽  
Dosing Interval ◽  
Selection Window ◽  
Mutant Prevention Concentration

ABSTRACT To study the hypothesis of the mutant selection window (MSW) in a pharmacodynamic context, the susceptibility of a clinical isolate of methicillin-resistant Staphylococcus aureus exposed to moxifloxacin (MOX), gatifloxacin (GAT), levofloxacin (LEV), and ciprofloxacin (CIP) was tested daily by using an in vitro dynamic model that simulates human pharmacokinetics. A series of monoexponential pharmacokinetic profiles that mimic once-daily administration of MOX (half-life, 12 h), GAT (half-life, 7 h), and LEV (half-life, 6.8 h) and twice-daily administration of CIP (half-life, 4 h) provided peak concentrations (C max) that either equaled the MIC, fell between the MIC and the mutant prevention concentration (MPC) (i.e., within or “inside” the MSW), or exceeded the MPC. The respective ratios of the area under the curve (AUC) over a 24-h dosing interval (AUC24) to the MIC varied from 13 to 244 h, and the starting inoculum was 108 CFU/ml (6 × 109 CFU per 60-ml central compartment). With all four quinolones, the greatest increases in MIC were observed at those AUC24/MIC values (from 24 to 62 h) that corresponded to quinolone concentrations within the MSW over most of the dosing interval (>20%). Less-pronounced increases in MIC were associated with the smallest simulated AUC24/MIC values (15 to 16 h) of GAT and CIP, whose C max exceeded the MICs. No such increases were observed with the smallest AUC24/MIC values (13 to 17 h) of MOX and LEV, whose C max were close to the MICs. Also, less pronounced but significant increases in MIC occurred at AUC24/MIC values (107 to 123 h) that correspond to quinolone concentrations partly overlapping the MIC-to-MPC range. With all four drugs, no change in MIC was seen at the highest AUC24/MIC values (201 to 244 h), where quinolone concentrations exceeded the MPC over most of the dosing interval. These “protective” AUC24/MIC ratios correspond to 66% of the usual clinical dose of MOX (400 mg), 190% of a 400-mg dose of GAT, 220% of a 500-mg dose of LEV, and 420% of two 500-mg doses of CIP. Thus, MOX may protect against resistance development at subtherapeutic doses, whereas GAT, LEV, and CIP provide similar effects only at doses that exceed their usual clinical doses. These data support the concept that resistant mutants are selectively enriched when antibiotic concentrations fall inside the MSW and suggest that in vitro dynamic models can be used to predict the relative abilities of quinolones to prevent mutant selection.

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