Topoisomerase II and IV QuinoloneResistance-Determining Regions in Stenotrophomonas maltophilia Clinical Isolates with Different Levels of QuinoloneSusceptibility

Abstract

The quinolone resistance-determining regions (QRDRs) of topoisomerase II and IV genes from Stenotrophomonas maltophilia ATCC 13637 were sequenced and compared with the corresponding regions of 32 unrelated S. maltophilia clinical strains for which ciprofloxacin MICs ranged from 0.1 to 64 g/ml. GyrA (Leu-55 to Gln-155, Escherichia coli numbering), GyrB (Met-391 to Phe-513), ParC (Ile-34 to Arg-124), and ParE (Leu-396 to Leu-567) fragments from strain ATCC 13637 showed high degrees of identity to the corresponding regions from the phytopathogen Xylella fastidiosa, with the degrees of identity ranging from 85.0 to 93.5%. Lower degrees of identity to the corresponding regions from Pseudomonas aeruginosa (70.9 to 88.6%) and E. coli (73.0 to 88.6%) were observed. Amino acid changes were present in GyrA fragments from 9 of the 32 strains at positions 70, 85, 90, 103, 112, 113, 119, and 124; but there was no consistent relation to higher ciprofloxacin MICs. The absence of changes at positions 83 and 87, commonly involved in quinolone resistance in gram-negative bacteria, was unexpected. The GyrB sequences were identical in all strains, and only one strain (ciprofloxacin MIC, 16 g/ml) showed a ParC amino acid change (Ser-803Arg). In contrast, a high frequency (16 of 32 strains) of amino acid replacements was present in ParE. The frequencies of alterations at positions 437, 465, 477, and 485 were higher (P < 0.05) in strains from cystic fibrosis patients, but these changes were not linked with high ciprofloxacin MICs. An efflux phenotype, screened by the detection of decreases of at least twofold doubling dilutions of the ciprofloxacin MIC in the presence of carbonyl cyanide m-chlorophenylhydrazone (0.5 g/ml) or reserpine (10 g/ml), was suspected in seven strains. These results suggest that topoisomerases II and IV may not be the primary targets involved in quinolone resistance in S. maltophilia.

Detection of the Smqnr quinolone protection gene and its prevalence in clinical isolates of Stenotrophomonas maltophilia in China

“…Although mutations of the gyrA and parE genes at common sites were found in half of the drug-resistant strains, some previous publications have indicated that mutations at these sites are not related to the drug resistance of S. maltophilia Valdezate et al, 2002).…”

“…Resistance to quinolones is mainly the result of chromosomally mediated mechanisms, including mutations in the targets of quinolones (DNA gyrase and topoisomerase IV) and decreased accumulation of quinolones (as a result of porin alteration or overexpression of efflux pump systems) Valdezate et al, 2002). It has also been found that quinolone resistance can be caused by plasmid-mediated quinolone resistance (PMQR) determinants, and the genes responsible for such resistance are named qnr .…”

Phenotypic and Molecular Characterization of Acinetobacter Clinical Isolates Obtained from Inmates of California Correctional Facilities

“…Resistance to FQs in Gram-negative bacteria primarily results from point mutations in gyrA and/or parC gene sequences that render significantly lower drug affinity for DNA gyrase (containing mutated GyrA) and DNA topoisomerase (composed of mutated ParC) (1,57,65). In A. baumannii, the most common amino acid substitutions occur at position 83 of GyrA and position 80 of ParC (31,72,73,76).…”

Phenotypic and Molecular Characterization ofAcinetobacter baumanniiClinical Isolates from Nosocomial Outbreaks in Los Angeles County, California

“…A major mechanism of fluoroquinolone resistance in gramnegative bacteria involves changes in the structure (and hence in the affinity to the drugs) of the drug targets DNA gyrase (encoded by the gyrA and gyrB genes) and DNA topoisomerase IV (encoded by the parC and parE genes) (1,35,45). Specifically, amino acid substitutions at certain positions in subunits A (GyrA and ParC) of both DNA gyrase and DNA topoisomerase IV, due to point mutations in the QRDRs of the genes encoding these two polypeptides, have been found to contribute to fluoroquinolone resistance.…”