We have developed a fluorescence resonance energy transfer (FRET)-based assay to detect ciprofloxacin resistant (Cp(r)) mutants of the biothreat agent Yersinia pestis. We selected spontaneous mutants of the attenuated Y. pestis KIM 5 strain that were resistant to a ciprofloxacin (CIP) concentration of at least 1 microg/ml. DNA sequencing of gyrA encoded by 65 of these mutants revealed that all ...

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. I...

BACKGROUND Previous work showed that piperazinyl-cross-linked ciprofloxacin dimer exhibits good bacteriostatic activity with Streptococcus pneumoniae and Staphylococcus aureus; lethal activity was not measured. Subsequently, the dimer failed to kill Mycobacterium smegmatis but blocked growth. Whether the compound is lethal with non-mycobacterial species is not known. METHODS Bacteriostatic an...

OBJECTIVES Salmonella enterica isolates of six serovars and mutants obtained during determination of mutant prevention concentrations (MPCs) were investigated for mechanisms of decreased susceptibility to fluoroquinolones. METHODS The quinolone resistance determining regions (QRDRs) of gyrA, gyrB, parC and parE genes were sequenced. MIC values were determined in the presence/absence of the ef...

Fluoroquinolones acting equally through DNA gyrase and topoisomerase IV in vivo are considered desirable in requiring two target mutations for emergence of resistant bacteria. To investigate this idea, we have studied the response of Staphylococcus aureus RN4220 to stepwise challenge with sparfloxacin, a known dual-target agent, and with NSFQ-105, a more potent sulfanilyl fluoroquinolone that b...

Fluoroquinolones form drug-topoisomerase-DNA complexes that rapidly block transcription and replication. Crystallographic and biochemical studies show that quinolone binding involves a water/metal-ion bridge between the quinolone C3-C4 keto-acid and amino acids in helix-4 of the target proteins, GyrA (gyrase) and ParC (topoisomerase IV). A recent cross-linking study revealed a second drug-bindi...

OBJECTIVES The objective of this study was to determine the contribution of the CmeABC efflux pump to the emergence of fluoroquinolone (FQ)-resistant mutants in Campylobacter jejuni under various levels of selection pressure. METHODS The frequency of emergence of ciprofloxacin-resistant mutants was measured in wild-type C. jejuni NCTC 11168 and its isogenic cmeB mutant and cmeR mutant (overex...

OBJECTIVES Mutations in the gyrase genes cause fluoroquinolone resistance in Mycobacterium tuberculosis. However, the predictive value of these markers for clinical outcomes in patients with MDR-TB is unknown to date. The objective of this study was to determine molecular markers and breakpoints predicting second-line treatment outcomes in M. tuberculosis patients treated with fourth-generation...

To obtain a general framework for understanding selection of antibiotic-resistant mutants, allelic diversity was examined with about 600 fluoroquinolone-resistant mutants of mycobacteria. Selection at low fluoroquinolone concentration produced many low-level resistance mutants. Some of these contained mutations that conferred unselected antibiotic resistance; none contained alterations in the q...

Oxolinic acid (OA) resistance in field isolates of Burkholderia glumae, a causal agent of bacterial grain rot, is dependent on an amino acid substitution at position 83 in GyrA (GyrA83). In the present study, among spontaneous in vitro mutants from the OA-sensitive B. glumae strain Pg-10, we selected OA-resistant mutants that emerged at a rate of 5.7 x 10(-10). Nucleotide sequence analysis of t...