Streptococcus pneumoniae has consistently become more resistant to primary, orally administered treatment regimens used for community-acquired
respiratory tract infections (CARTI;
sinusitis,
bronchitis,
pneumonia). As resistance rates approach 40-50% in the United States and North America for
penicillin and
macrolides, other agents also have exhibited coresistance rates of 10-20% (
tetracycline,
clindamycin,
trimethoprim/sulfamethoxazole). These facts led to altered clinical treatment guidelines (IDSA) supporting the use of respiratory
fluoroquinolones (
levofloxacin,
gatifloxacin,
gemifloxacin, and
moxifloxacin). This report from the SENTRY Antimicrobial Surveillance Program lists possible parenterally administered treatment alternatives for the
fluoroquinolone (
levofloxacin)-nonsusceptible pneumococci. The SENTRY Program isolates from CARTI (1997-2003), totaling 21605 strains from Europe, Asia Pacific, and the Americas, were screened for
fluoroquinolone-resistant S. pneumoniae. A total of 157 (0.7%)
levofloxacin-nonsusceptible (MIC > or = 4 microg/mL) strains were identified and tested by reference broth microdilution methods against 27 antimicrobials.
Quinolone resistance-determining region (QRDR) mutations were determined by PCR amplification and gene sequencing. The entire population of S. pneumoniae had the following antibiogram demographics:
penicillin-nonsusceptible (32%),
macrolide resistance (24%), tetracycline resistance (21%),
clindamycin resistance (11%),
trimethoprim/sulfamethoxazole resistance (33%), and 6% of strains were resistant to all 5 drugs.
Levofloxacin-resistant strains routinely had 2 or more QRDR mutations most frequently in gyrA at Ser81Phe or Tyr and in parC at Ser79Phe or Tyr and Lys137Asn. Four agents had extremely low rates of resistance when tested against the 157
levofloxacin-nonsusceptible strains (e.g.,
quinupristin/dalfopristin, 0% resistance;
vancomycin, 0%;
cefepime, 1%;
ceftriaxone, 1%).
Levofloxacin-nonsusceptible pneumococcal isolates remain uncommon, but are a growing problem in CARTI (1.4% in 2003), especially in previously
fluoroquinolone-treated cases. Parenteral
cephalosporins (
cefepime or
ceftriaxone) continue to be potent and safe for use in hospitalized patients with S. pneumoniae community-acquired
pneumonia, used with or without co-drugs according to published guidelines.