In vitro susceptibility of six fluoroquinolones against invasive Streptococcus pneumoniae isolated from 1996 to 2001 in Taiwan

A total of 331 invasive nonduplicated Streptococcus pneumoniae isolates from three sampling periods during 1996 to 2001 were tested for susceptibility to recently developed fluoroquinolones. Five major serotypes, 23F, 6B, 14, 19F, and 3, were frequently encountered in this collection. Penicillin nonsusceptible isolates constituted 52.9% from 1996 to 1997, 61.6% from 1998 to 1999, and 60.0% from 2000 to 2001. Fifty-seven percent of the isolates were susceptible to cefotaxime, 56.5% to ceftriaxone, 54.1% to cefepime, and 52.6% to cefuroxime. Macrolide-susceptible isolates constituted less than 14% of the total sample, and no vancomycin-resistant isolates were detected. For fluoroquinolones, MIC90 was lowest for gemifloxacin (MIC90 = < or = 0.12 microg/ml), followed by moxifloxacin (MIC90 = 0.25 microg/ml), gatifloxacin (MIC90 = 0.5 microg/ml), sparfloxacin (MIC90 = 0.5 microg/ml), levofloxacin (MIC90 = 1 microg/ml), and ciprofloxacin (MIC90 = 2 microg/ml). All isolates were susceptible to sparfloxacin, levofloxacin, gatifloxacin, and gemifloxacin apart from one isolate (0.3%), which was simultaneously resistant to sparfloxacin, levofloxacin, and gatifloxacin. Mutations at the positions S81F of GyrA and D435N and I460V of ParC were detected for this multiple drug resistant isolate. The in vitro results suggest that recently developed fluoroquinolones are very effective against invasive S. pneumoniae isolates in Taiwan. Nevertheless, emerging fluoroquinolone resistance should be acknowledged and clinicians alerted. Surveillance should be carried out to monitor any changes in antibiotic resistance of S. pneumoniae.