Among 73 clinical isolates of Pseudomonas aeruginosa 48 strains were ciprofloxacine (CIP) susceptible and 25 CIP resistant (Minimal inhibitory concentration--MIC>32 microg/ml - 14 strains) or of intermediate susceptibility to CIP (MIC > or = 1,5 - 32 microg/ml - 11 isolates). Mutations in the quinolone-resistance-determining region (QRDR) of gyrA gene were searched in groups of CIP resistant an...

Eighteen quinolone-resistant isolates of Escherichia coli were selected by exposing ten clinical isolates to increasing concentrations of norfloxacin and lomefloxacin. The mutant isolates showed a multiple-antibiotic-resistance phenotype. All of them contained single mutations in gyrA consisting of the substitution of Ser-83-->Leu (n = 14), Val (n = 1) or Ala (n = 1) and the substitution of Asp...

Conventional wisdom holds that the best way to treat infection with antibiotics is to 'hit early and hit hard'. A favoured strategy is to deploy two antibiotics that produce a stronger effect in combination than if either drug were used alone. But are such synergistic combinations necessarily optimal? We combine mathematical modelling, evolution experiments, whole genome sequencing and genetic ...

The minimum inhibitory concentrations (MICs), mutation prevention concentrations (MPCs) and contribution of quinolone resistance-determining region (QRDR) mutations to fluoroquinolone (ciprofloxacin, enrofloxacin and orbifloxacin) susceptibility in 23 Pasteurella multocida (Pm) isolates were investigated. Fluoroquinolone-susceptible isolates (MICs ≤0.25 µg/ml, 9 isolates) had no QRDR mutations,...

OBJECTIVES To investigate quinolone resistance mechanisms in an Escherichia coli clinical isolate (Ar2) resistant to ofloxacin but susceptible to nalidixic acid selected after 10 days of ofloxacin therapy in a patient with prostatitis. METHODS Molecular typing (ERIC-PCR and RAPD), antibiotic susceptibility and gyrA, gyrB, parC and parE QRDR sequences were compared for E. coli Ar2 and a wild-t...

Staphylococcus aureus BM4626 (ciprofloxacin MIC, 0.5 microgram/ml) and BM4627 (ciprofloxacin MIC, 32 microgram/ml) were isolated from the same patient before and during pefloxcin therapy for septic tibial nonunion, respectively. The two strains had similar serotypes and indistinguishable phage types and SmaI-generated restriction fragment length polymorphisms. Portions of the gyrA (codons 60 to...

MarA47(Yp) from Yersinia pestis, showing 47% identity to Escherichia coli MarA in its N terminus, caused resistance to antibiotics and to organic solvents when expressed in both E. coli and Y. pestis. Resistance was linked to increased expression of the AcrAB multidrug efflux pump. In four of five spontaneous multidrug-resistant mutants of Y. pestis independently selected by growth on tetracycl...

Previous studies showed that nonsense mutations in either of two genes (capR or capS) or an undefined mutation in a third gene (capT) led to pleiotropic effects: (i) increased capsular polysaccharide synthesis (mucoid phenotype); (ii) increased synthesis of enzymes specified by at least four spatially separated operons involved in synthesis of capsular polysaccharide including the product of th...

The distribution of fluoroquinolone resistance-associated point mutations in genes encoding the subunits of DNA gyrase and DNA topoisomerase i.v. was examined in 110 clinical isolates of Staphylococcus aureus. Point mutations were detected by polymerase chain reaction (PCR) and restriction fragment length polymorphism analysis and mutations were further characterized by sequencing of PCR produc...