Prevalence and Antibacterial Susceptibility of mef (A)-Positive Macrolide-Resistant Streptococcus pneumoniae over 4 Years (2000 to 2004) of the PROTEKT US Study

In the United States, approximately 30% of Streptococcus pneumoniae isolates are macrolide (erythromycin [ERY]) resistant (ERSP), most commonly due to expression of the mef (A) gene previously associated with lower-level ERY resistance (ERY r ; MIC = 1 to 4 μg/ml). The data from the PROTEKT US surveillance study were analyzed to evaluate the prevalence and antibacterial susceptibility of mef (A)-positive ERSP. In all, 26,634 isolates of S. pneumoniae were collected in the United States between 2000 and 2004 from centers common to all years. ERY r was stable at approximately 29% over the 4 years, but the proportion of ERSP isolates positive for mef (A) alone decreased (year 1 [2000 to 2001], 69.0%; year 4 [2003 to 2004], 60.7%), with the sharpest declines seen in isolates from patients from 0 to 2 years of age. Conversely, the proportion isolates positive for both erm (B) and mef (A) increased over the duration of the present study (year 1, 9.3%; year 4, 19.1%), a change that was again most marked in patients aged ≤2 years. The majority of ERSP isolates expressing mef (A) alone exhibited higher than previously reported levels of ERY r (MIC 90 = 16 μg/ml). However, the ketolide antibacterial telithromycin consistently demonstrated in vitro activity against these isolates over the 4 years of the study (MIC 90 = 0.5 to 1 μg/ml).