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,...

High-level quinolone resistance in Enterococcus faecium was associated with mutations in both gyrA and parC genes in 10 of 11 resistant strains. On low-level resistant strain without such mutations may instead possess an efflux mechanism or alterations in the other subunits of the gyrase or topoisomerase IV genes. These findings are similar to those for other gram-positive bacteria, such as Ent...

The problem of Pseudomonas aeruginosa resistance to fluoroquinolones is of growing concern in hospitals. The major mechanism of the resistance of this bacterium to fluoroquinolones is the modification of type II topoisomerases (DNA gyrase and topoisomerase IV). In this study, we examined, using the technique of DNA pyrosequencing, mutations in the quinolone resistance-determining regions of the...

This work demonstrates that Vibrio vulnificus biotype 2, serovar E, an eel pathogen able to infect humans, can become resistant to quinolone by specific mutations in gyrA (substitution of isoleucine for serine at position 83) and to some fluoroquinolones by additional mutations in parC (substitution of lysine for serine at position 85). Thus, to avoid the selection of resistant strains that are...

Over 124 methicillin-susceptible Staphylococcus aureus 0/74 fluoroquinolone-susceptible versus 5/50 fluoroquinolone-resistant isolates were hypermutable. Hypermutable isolates combined mutations in gyrA, parC, and/or parE genes. One strain had a large deletion of the mutator mutS and mutL genes. No relevant mutation in mutS and mutL genes was found in the other isolates.

The parC and gyrA genes of 73 ciprofloxacin-resistant and 6 ciprofloxacin-susceptible Enterococcus faecium clinical isolates were partly sequenced. Alterations in ParC and GyrA, possibly in combination with other resistance mechanisms, severely restricted the in vitro activities of the nine quinolones tested. For all isolates, clinafloxacin and sitafloxacin showed the best activities.

We report the first case of naturally occurring fluoroquinolone resistance in Ureaplasma spp. from the United States. Resistance in this case probably developed as a result of mutations in the gyrA and parC genes of the DNA gyrase/topoisomerase IV complex that occurred in the presence of antimicrobial selective pressure.

The activity of ciprofloxacin, sparfloxacin and moxifloxacin was determined for 205 Enterococcus faecalis isolates from patients of five hospitals (Warsaw, Poland; collected from 2000 to 2002). Ciprofloxacin resistant and intermediate isolates were numerous (53.7%). Among them, highly resistant (MIC > or = 16 mg/l) isolates predominated (98%). Isolates resistant to ciprofloxacin were also resis...

Among 155 clinical respiratory isolates of Haemophilus influenzae in Korea, 6 (3.9%) isolates had reduced levofloxacin susceptibility (MICs ≥ 0.5 μg/mL). These six isolates had no significant quinolone resistance-determining region (QRDR) mutations in gyrA, gyrB, parC, or parE. This phenomenon suggests that neither evolution nor spread of any significant QRDRs mutations in clinical isolates occ...