Abstract
ABSTRACT
Penicillin-resistant oral streptococci constitute the genetic reservoir for β-lactam resistance in S. pneumoniae. Here we report the isolation of clinical strains of S. mitis with unusually high MIC values for β-lactam antibiotics; resistance to benzylpenicillin was 64 μg/ml and to cefotaxime 128 μg/ml. Among the β-lactam compounds tested, only the carbapenems imipenem and meropenem showed MICs below 32 μg/ml. Both S. mitis strains were resistant to tetracycline and were highly resistant to aminoglycosides. Pulse field mapping of chromosomal DNA revealed identical patterns in both strains, indicating clonal identity of the two isolates. Using chromosomal S. mitis DNA, the laboratory strain S. pneumoniae R6 could be transformed in four successive steps to cefotaxime and benzylpenicillin resistance of 64 μg/ml. The results exemplify the importance of commensal streptococci for the development of cefotaxime resistance in S. pneumoniae.
Get full access to this article
View all access options for this article.