Abstract
Abstract: :
Purpose: S. pneumoniae susceptibility to levofloxacin (LVX) has remained high (>99%) according to US surveillance data. The prevalence of single–step QRDR mutations in S. pneumoniae over a 5–year period was studied, using isolates from institutions participating in TRUST (Tracking Resistance in the United States Today), the largest longitudinal continuous surveillance program for antimicrobial resistance in the US. Methods: All 1104 (LVX)–susceptible pneumococci (MIC90 <2.0 µg/mL) from 9 institutions in 9 states participating in surveillance studies during 1999, 2001, and 2003 respiratory seasons were screened for QRDR mutations. Strains were screened with pyrosequencing technology (PCR and DNA sequencing analysis) for parC, gyrA, and parE mutations. Strains were screened for mutations at Asp78, Ser79, and Asp83 hot spots in parC; Asp80, Ser81, and Glu85 in gyrA; and Asp435 in parE. Results: LVX MIC90 distribution of isolates from the 9 institutions was similar to distribution in isolates from >200 institutions participating in each surveillance study. Over the 5–year period, four (0.4%) single–step QRDR mutants were found among the 1104 LVX–susceptible isolates. Institutions with a single–step QRDR mutant in 1 year did not have any mutants the following year. Mutations were limited to parE and parC genes, causing resistance to ciprofloxacin (CIP) but not to LVX. There was no evidence of clonal spread of single–step QRDR mutants. Conclusions: S. pneumoniae isolates with QRDR single–step mutations are infrequent (<1%) in the US and show resistance to CIP but not to LVX. These data are consistent with surveillance study data showing that S. pneumoniae susceptibility to LVX remains high (>99%) despite increased use of LVX over 8 years (1997–2004).
Keywords: antibiotics/antifungals/antiparasitics • clinical laboratory testing • mutations