BACKGROUND The mutant prevention concentration (MPC) is an important parameter to evaluate the likelihood of growth of fluoroquinolone-resistant mutants for antimicrobial-pathogen combinations. The MPCs of fluoroquinolones for different canine pathogens have not been compared. In this study, we compared for the first time orbifloxacin MPCs between susceptible strains of Escherichia coli, Pseudo...

To date several classes of multidrug exporters have been identifi ed in prokaryotic cells, one of which is the resistance nodulation division (RND) family transporters (Poole and Srikumar, 2001). In this type of effl ux system, RND, an inner membrane proton-drug antiporter, forms a tripartite construct with a channel-forming outer membrane protein and an inner membrane protein of the MFP (membr...

A general search has been made for mutants defective in their ability to derepress the histidine operon. The procedure was to select for mutants with an increased sensitivity to the false feedback inhibitor, 2-thiazolealanine. Five mutant strains defective in derepression have been isolated. All five strains are unable to derepress normally because of mutations located in the operator-promoter ...

The cel (cellobiose utilization) operon of Escherichia coli K12 is not expressed in the wild-type organism. However, mutants that can express the operon and thereby utilize the P-glucoside sugars cellobiose, arbutin and salicin are easily isolated. Two kinds of mutations are capable of activating the operon. The first involves mutations that allow the repressor to recognize the substrates cello...

The E-arabinose operon is under both positive and negative control by the product of its regulatory gene, UrQc. We have measured transcription of the arabinose genes by hybridization of 3H-labeled messenger RNA to single-stranded DNA from an arabinose transducing phage in order to study the effect of the regulatory gene on transcription. In strains in which the arabinose regulatory gene is comp...

The E-arabinose operon is under both positive and negative control by the product of its regulatory gene, UrQc. We have measured transcription of the arabinose genes by hybridization of 3H-labeled messenger RNA to single-stranded DNA from an arabinose transducing phage in order to study the effect of the regulatory gene on transcription. In strains in which the arabinose regulatory gene is comp...

The contribution of regulatory genes to fluoroquinolone resistance was studied with clinical Escherichia coli strains bearing mutations in gyrA and parC and with different levels of fluoroquinolone resistance. Expression of marA and soxS was evaluated by Northern blot analysis of isolates that demonstrated increased organic solvent tolerance, a phenotype that has been linked to overexpression o...

OBJECTIVES The purpose of this study was to characterize decreased susceptibility to tigecycline in clinical isolates of Escherichia coli obtained during Phase 3 clinical trials. METHODS Gene expression was analysed by transcriptional profile analysis and RT-PCR. Transposon mutagenesis with IS903kan was used for selection of transposon mutants. Transposon insertions were mapped by DNA sequenc...

Spontaneous quinolone-resistant mutants obtained from Salmonella typhimurium Su694 were screened for mutations by direct DNA sequencing of an amplified PCR gyrA fragment. Substitutions Ser-83-->Phe (Ser83Phe), Ser83Tyr, Asp87Tyr, and Asp87Asn and double mutation Ala67Pro-Gly81Ser, which resulted in decreased sensitivities to ciprofloxacin, enoxacin, pefloxacin, norfloxacin, ofloxacin, and nalid...

The responses of hypermutable Escherichia coli strains to selection with antibiotics having different endogenous resistance potentials were determined. Selections with rifampicin or ciprofloxacin at 4 x MIC, i.e. conditions where they act as single target agents against RpoB and GyrA, respectively, demonstrated that some hypermutators generated resistant mutants with frequencies up to 1000-fold...