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During the past 6 to 7 years, the problem of antimicrobial resistance in Streptococcus pneumoniae has grown dramatically in the United States. Currently, approximately 26.5% of pneumococcal isolates express intermediate levels of resistance to penicillin; approximately 17.5% are highly penicillin resistant. We studied whether clonal relationships exist among current isolates of high-level penicillin-resistant S. pneumoniae (PRSP) in the United States. One hundred forty-seven PRSP isolates recovered in a 30-center surveillance study in the United States during 1994-1995 were characterized with respect to serotype, antimicrobial susceptibility pattern, and pulsed-field gel electrophoresis (PFGE) profile. Only six serotypes were observed among the 147 PRSP isolates examined in this study: 6A, 6B, 9A, 14, 19F, and 23F. One hundred three (70.1%) of the 147 strains were characterized by one of only nine PFGE types; 76 (51.7%) of the 147 isolates were characterized by only four PFGE profiles. Currently in the United States, most PRSP strains are represented by relatively few clonal groups.

Original publication




Journal article


Clinical Infectious Diseases: An Official Publication of the Infectious Diseases Society of America

Publication Date





757 - 761


University of Massachusetts Medical Center, Worcester, USA.


Humans, Streptococcus pneumoniae, DNA, Bacterial, Electrophoresis, Gel, Pulsed-Field, Penicillin Resistance, United States