We isolated spontaneous mutants from Escherichia coli K-12 with low-level resistance to norfloxacin. These mutants were classified into the following three types on the basis of their properties: (i) NorA appeared to result for mutation in the gyrA locus for the A subunit of DNA gyrase; (ii) NorB showed low-level resistance to quinolones and other antimicrobial agents (e.g., cefoxitin, chloramp...

MgrA is a known regulator of the expression of several multidrug transporters in Staphylococcus aureus. We identified another regulator of multiple efflux pumps, NorG, by its ability, like that of MgrA, to bind specifically to the promoter of the gene encoding the NorA efflux pump. NorG is a member of the family of the GntR-like transcriptional regulators, and it binds specifically to the putat...

OBJECTIVES Although the prevalence of fluoroquinolone resistance among methicillin-resistant Staphylococcus aureus (MRSA) is known to be higher than in methicillin-susceptible S. aureus (MSSA), the reasons have never been identified. METHODS We randomly selected 115 isolates of S. aureus collected from 10 different hospitals in Korea between June 2009 and May 2011. To investigate the differen...

The genes for a nitric oxide reductase-like cytochrome bc complex were cloned from a thermophilic, chemolithoautotrophic hydrogen-oxidizing bacterium, Hydrogenobacter thermophilus TK-6. The structural genes norC and norB, which encode cytochrome c and cytochrome b subunits of the complex respectively, are probably transcribed as a tricistronic operon with a following gene encoding a putative me...

A PCR-based approach was developed to recover nitric oxide (NO) reductase (norB) genes as a functional marker gene for denitrifying bacteria. norB database sequences grouped in two very distinct branches. One encodes the quinol-oxidizing single-subunit class (qNorB), while the other class is a cytochrome bc-type complex (cNorB). The latter oxidizes cytochrome c, and the gene is localized adjace...

The gene encoding a nitric oxide reductase has been identified in Neisseria gonorrhoeae. The norB gene product shares significant identity with the nitric oxide reductases in Ralstonia eutropha and Synechocystis sp. and, like those organisms, the gonococcus lacks a norC homolog. The gonococcal norB gene was found to be required for anaerobic growth, but the absence of norB did not dramatically ...

Efflux is an important resistance mechanism in Staphylococcus aureus, but its frequency in patients with bacteremia is unknown. Nonreplicate bloodstream isolates were collected over an 8-month period, and MICs of four common efflux pump substrates, with and without the broad-spectrum efflux pump inhibitor reserpine, were determined (n = 232). A reserpine-associated fourfold decrease in MIC was ...

A gene cluster which includes genes required for the expression of nitric oxide reductase in Rhodobacter sphaeroides 2.4.3 has been isolated and characterized. Sequence analysis indicates that the two proximal genes in the cluster are the Nor structural genes. These two genes and four distal genes apparently constitute an operon. Mutational analysis indicates that the two structural genes, norC...

Reduction of NO to N2O by denitrifiying bacteria is catalyzed either by a monomeric quinol-nitric oxide reductase (qNor) or by a heterodimeric cytochrome c-dependent nitric oxide reductase (cNor). In ancient thermophilic bacteria belonging to the Thermales and Aquificales phylogenetic groups, the cluster encoding the cNor includes a small third gene (norH), in addition to those encoding homolog...