Fluoroquinolone-Resistant Mutants of Burkholderia cepacia

DOI: 10.1128/AAC.00799-07

Article Figures & Data

Open in new tab
Download powerpoint
FIG. 1.
Effect of topoisomerase mutations on the survival of B. cepacia in water. Survival of B. cepacia in water was not affected by mutation in gyrase subunit A or topoisomerase IV. Error bars indicate the standard errors of the means. Differences in survival are not significant.
Open in new tab
Download powerpoint
FIG. 2.
Effect of topoisomerase mutations on the survival of B. cepacia on dry surfaces. Survival of B. cepacia in water was not affected by mutation in gyrase subunit A or topoisomerase IV. Error bars indicate the standard errors of the means. Error bars are not shown if obscured by the symbol. Differences in survival are not significant.

TABLE 1.

Primers used to amplify the QRDRs of the topoisomerase genes of B. cepacia

Gene	Primer positions^a	Sequence (5′-3′)	Amplicon size (bp)
gyrA	62-81	5′ ATCTCGATTACGCGATGAGC	449
	493-511	5′ GCCGTTGATCAGCAGGTT
gyrB	1127-1146	5′ GAGGAAGTTGTGGCGAAGG	400
	1502-1520	5′ AGTCTTCCTTGCCGATGC
parC	98-118	5′ ATTGGTCAGGGTCGTGAAGA	229
	295-315	5′ GTAGCGCAGCGAGAAATCCT
parE	1178-1198	5′ CAGGGCAAGGTAGTCGAAAA	380
	1557-1577	5′ GTGAGCAGCAAGGTCTGGAT

TABLE 2.

Characteristics of fluoroquinolone-resistant B. cepacia mutants selected in vitro^a

Strain	Mutation rate (mutation/division)	MIC (μg/μl)	Selection step	Sequence found in QRDRs of:				Generation time [min (95% confidence interval)]	P value	Relative fitness (±SEM)^b	P value
Strain	Mutation rate (mutation/division)	MIC (μg/μl)	Selection step	gyrA	gyrB	parC	parE	Generation time [min (95% confidence interval)]	P value	Relative fitness (±SEM)^b	P value
WT		1		WT	WT	WT	WT	38.0 (37.06-38.94)
F1 mutant	9.6 × 10⁻¹¹	12	1st	Asp87Asn	WT	WT	WT	37.0 (36.77-37.23)	0.331	1.01 ± 0.01	0.831
F2 mutant	9.6 × 10⁻¹¹	64	1st	Thr83Ile	WT	WT	WT	37.1 (36.9-37.3)	0.377	1.01 ± 0.152	0.868
F3 mutant	1.1 × 10⁻¹⁰	>256	2nd	Asp87Asn	WT	Ser80Leu	WT	43.0 (41.85-44.15)	0.004	0.80 ± 0.12	0.003
F4 mutant	6.8 × 10⁻¹⁰	>256	2nd	Thr83Ile	WT	Ser80Leu	WT	45.7 (44.2-47.2)	0.001	0.78 ± 0.18	0.002

↵ a Strain F1 was isolated on 2 μg/ml ciprofloxacin (2× MIC); F2 was isolated on 6 μg/ml (6× MIC), F3 was isolated on 24 μg/ml ciprofloxacin by the use of F1 as the starting point; F4 was isolated on 128 μg/ml ciprofloxacin by the use of F2 as the starting point. The statistical significance of generation time differences is shown by a P value. WT, wild type.
↵ b Competition assays were used to measure the fitness of the fluoroquinolone mutants relative to that of the susceptible parent.