In vitro activity of sitafloxacin against clinical strains of Streptococcus pneumoniae with defined amino acid substitutions in QRDRs of gyrase A and topoisomerase IV.
OBJECTIVE
Fluoroquinolone-resistant Streptococcus pneumoniae are increasing worldwide rapidly. In vitro activities of sitafloxacin were evaluated against clinical isolates of S. pneumoniae resistant to levofloxacin (MIC of levofloxacin > or = 4 mg/L), which were characterized genetically.


METHODS
The quinolone resistance determining regions (QRDRs) of gyrA, gyrB, parC and parE of these strains were analysed by PCR-based sequencing. MICs of sitafloxacin and other quinolones were determined by a microdilution broth method.


RESULTS
All 18 strains had at least one amino acid substitution in the QRDRs of GyrA and ParC, which included Ser-81-->Tyr/Phe and Glu-85-->Lys in GyrA and Ser-79-->Phe/Ile/Tyr, Asp-83-->Tyr, Asn-91-->Asp, Ser-107-->Phe, Lys-137-->Asn and Ala-142-->Ser in ParC. Most isolates had Asp-435-->Asn/Ile-460-->Val/Ala-596-->Thr substitutions in ParE, while no amino acid substitution in GyrB was noted in all isolates. Ten isolates for which levofloxacin MICs were 16 or 32 mg/L had multiple mutations in both GyrA and ParC. The MIC80 value of sitafloxacin for levofloxacin-resistant isolates was 0.25 mg/L. The range of MICs of sitafloxacin for isolates resistant to levofloxacin (MIC 4-32 mg/L) was 0.016-0.5 mg/L.


CONCLUSIONS
These findings warrant further studies to evaluate the usefulness of sitafloxacin in the treatment of levofloxacin-resistant S. pneumoniae infection.
Touyama
Masato
M
Department of Medicine and Therapeutics, Control and Prevention of Infectious Diseases, Graduate School of Medicine, University of the Ryukyus, 207 Uehara, Nishihara-cho, Okinawa 903-0215, Japan.
Higa
Futoshi
F
Nakasone
Chikara
C
Shinzato
Takashi
T
Akamine
Morikazu
M
Haranaga
Shusaku
S
Tateyama
Masao
M
Nakasone
Isamu
I
Yamane
Nobuhisa
N
Fujita
Jiro
J
D019943:Amino Acid Substitution / Q000235:genetics*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D027081:DNA Gyrase / Q000235:genetics*; D027101:DNA Topoisomerase IV / Q000235:genetics*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D024841:Fluoroquinolones / Q000494:pharmacology*; D064704:Levofloxacin; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000494:pharmacology; D017422:Sequence Analysis, DNA; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D024841:Fluoroquinolones; D064704:Levofloxacin; C076246:sitafloxacin; D015242:Ofloxacin; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase