The phylum Deinococcus-Thermus is a deeply-branching lineage of bacteria widely recognized as one of the most extremophilic. Members of the Thermus genus are of major interest due to both their bioremediation and biotechnology potentials. However, the molecular mechanisms associated with these key metabolic pathways remain unknown. Reverse-transcription quantitative PCR (RT-qPCR) is a high-thro...

BACKGROUND The purpose of this study was to determine the prevalence of fluoroquinolone resistance and quinolone resistance-determining region (QRDR) mutations among Streptococcus pneumoniae isolates in the United States during the period of 2001-2002. A second objective was to examine the genetic relatedness of pneumococcal isolates with parC and/or gyrA mutations during the period of 1994-200...

During the early 1990s, a clone of multiresistant Salmonella enterica serovar Typhimurium O5 negative (var. Copenhagen) of phage type DT204c predominated in Germany and neighboring countries within the calf-fattening industry. In addition to being resistant to ampicillin, kanamycin, tetracycline, chloramphenicol, and trimethoprim, these isolates were highly resistant to nalidixic acid (MIC 128 ...

The low prevalence of ciprofloxacin-resistant (Cp r) Streptococcus pneumoniae isolates carrying recombinant topoisomerase IV genes could be attributed to a fitness cost imposed by the horizontal transfer, which often implies the acquisition of larger-than-normal parE-parC intergenic regions. A study of the transcription of these genes and of the fitness cost for 24 isogenic Cp r strains was per...

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...

Mutations in quinolone targets were analysed in 80 unrelated nalidixic acid-resistant (NALR) Escherichia coli strains whose nalidixic acid and ciprofloxacin MICs ranged from 32 to >256 mg/L and 0.03-64 mg/L, respectively. These strains were isolated from food products (23) and faecal samples from humans (15) and healthy animals (42). Thirteen nalidixic acid-susceptible (NALS) E. coli strains we...

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...

Alternate mutations in the grlA and gyrA genes were observed through the first- to fourth-step mutants which were obtained from four Staphylococcus aureus strains by sequential selection with several fluoroquinolones. The increases in the MICs of gatifloxacin accompanying those mutational steps suggest that primary targets of gatifloxacin in the wild type and the first-, second-, and third-step...