title: Efflux and target mutations as quinolone resistance mechanisms in clinical isolates of Streptococcus pneumoniae.
abstract: The aim of this study was to characterize quinolone resistance mechanisms in strains of Streptococcus pneumoniae with increased MICs of ofloxacin. These strains were also tested for their susceptibility to a battery of quinolone antimicrobial agents, including gemifloxacin. Of the S. pneumoniae isolates used, 27 were susceptible to ofloxacin, 18 intermediate and 48 resistant (ofloxacin MIC <4, 4 and >4 mg/L, respectively). In general, the ofloxacin-susceptible strains had no amino acid substitutions in GyrA, GyrB, ParC or ParE. Moderate increases in MIC were associated with substitutions in the quinolone resistance-determining region (QRDR) of ParC, while the highest MICs were found for strains that also had substitutions in the QRDR of GyrA. The most common substitutions were Ser79-->Phe in ParC and Ser81-->Phe in GyrA. Other substitutions were identified within the QRDR of ParC and outside the QRDR of ParC and ParE; these did not appear to affect susceptibility. The effects of antimicrobial efflux pumps were studied by determining MICs of a range of quinolones in the presence and absence of reserpine, an inhibitor of Gram-positive efflux pumps. Our results indicated that high-level resistance, caused entirely by efflux, was seen in a minority of ofloxacin-resistant S. pneumoniae strains. Testing the susceptibility of quinolone-resistant strains to gemifloxacin, ciprofloxacin, norfloxacin, ofloxacin and trovafloxacin revealed that gemifloxacin was least affected by this large variety of resistance mechanisms and was the only quinolone with MICs of < or =0.5 mg/L for all strains in this study. These results suggest that gemifloxacin is highly potent against S. pneumoniae and may also be effective against strains resistant to other quinolones.
authors.affiliation: SmithKline Beecham Pharmaceuticals, Collegeville, PA 19426-0989, USA.
authors.forename: J
authors.initials: J
authors.lastname: Broskey
authors.forename: K
authors.initials: K
authors.lastname: Coleman
authors.forename: M N
authors.initials: MN
authors.lastname: Gwynn
authors.forename: L
authors.initials: L
authors.lastname: McCloskey
authors.forename: C
authors.initials: C
authors.lastname: Traini
authors.forename: L
authors.initials: L
authors.lastname: Voelker
authors.forename: R
authors.initials: R
authors.lastname: Warren
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D027081:DNA Gyrase; D027101:DNA Topoisomerase IV; D004250:DNA Topoisomerases, Type II / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D004352:Drug Resistance, Microbial; D024841:Fluoroquinolones; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000235:genetics
chemical_list: D000890:Anti-Infective Agents; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D024841:Fluoroquinolones; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II