Fluoroquinolone Resistance Mutations in the parC , parE , and gyrA Genes of Clinical Isolates of Viridans Group Streptococci

Abstract

The nucleotide sequences of the quinolone resistance-determining regions (QRDRs) of the parC and gyrA genes from seven ciprofloxacin-resistant (Cpr) isolates of viridans group streptococci (two high-level Cpr Streptococcus oralis and five low-level Cpr Streptococcus mitis isolates) were determined and compared with those obtained from susceptible isolates. The nucleotide sequences of the QRDRs of the parE and gyrBgenes from the five low-level Cpr S. mitisisolates and from the NCTC 12261 type strain were also analyzed. Four of these low-level Cpr isolates had changes affecting the subunits of DNA topoisomerase IV: three in Ser-79 (to Phe or Ile) of ParC and one in ParE at a position not previously described to be involved in quinolone resistance (Pro-424). One isolate did not show any mutation. The two high-level Cpr S. oralisisolates showed mutations affecting equivalent residue positions of ParC and GyrA, namely, Ser-79 to Phe and Ser-81 to Phe or Tyr, respectively. The parC mutations were able to transformStreptococcus pneumoniae to ciprofloxacin resistance, while the gyrA mutations transformed S. pneumoniaeonly when mutations in parC were present. These results suggest that DNA topoisomerase IV is a primary target of ciprofloxacin in viridans group streptococci, DNA gyrase being a secondary target.

Bacteremia Due to Viridans Group Streptococci with Diminished Susceptibility to Levofloxacin among Neutropenic Patients Receiving Levofloxacin Prophylaxis

“…Mutations in the quinolone resistance-determining region (QRDR) of gyrA, gyrB, and parC were determined by PCR amplification, followed by amplicon sequencing, as described elsewhere [15][16][17]. Multiple attempts at amplifying parE were unsuccessful.…”

“…Multiple attempts at amplifying parE were unsuccessful. Sequence data were analyzed with Sequencher 3.1.1 (GeneCodes), compared with the previously published QRDR of VG streptococci (GenBank accession numbers AF079198-AF079208 for gyrA, AF07925-AF079220 for gyrB, and AF079187-AF079197 for parC) [17], and deposited in GenBank (accession numbers AF393759-AF393779).…”

Quinolone resistance: Older concepts and newer developments

“…While the acquisition of topoisomerase mutations occurs initially by natural selection, recent reports suggest that the acquisition of resistance may also occur via the horizontal transfer of topoisomerase genes from resistant viridansgroup streptococci to S. pneumoniae [70][71][72]. A similar situation has been described for penicillin resistance in S. pneumoniae [73].…”

Species-level assessment of the molecular basis of fluoroquinolone resistance among viridans group streptococci causing bacteraemia in cancer patients

“…QRDRs were compared with the consensus sequence for Streptococcus pneumoniae (National Center for Biotechnology Information) given that a consensus sequence, or susceptible allele, has not been established for each VGS species. Polymorphisms in the VGS QRDRs were considered determinative if the polymorphisms had been previously described as contributing to fluoroquinolone resistance, or if the polymorphism was present in non-susceptible VGS strains with no other polymorphisms known to contribute to fluoroquinolone resistance [1,3,[6][7][8]. Polymorphisms not meeting these criteria were considered non-determinative.…”