A global gene pool for high-level cephalosporin resistance in commensal Streptococcus species and Streptococcus pneumoniae.

Highly penicillin- and cephalosporin-resistant Streptococcus mitis and Streptococcus oralis were isolated in Spain, Hungary, and Berlin. With chromosomal DNA of these strains, resistant transformants of Streptococcus pneumoniae were obtained that expressed low-affinity variants of penicillin-binding proteins (PBPs) 2x, 1a, 2a, and 2b in different combinations, depending on the selective conditions. The transformants had cefotaxime MICs of up to 6 microg/mL, and those with a low-affinity PBP 2b were highly deficient in penicillin-induced lysis. Sequence analysis of the pbp2x genes confirmed the presence of a global gene pool of penicillin resistance determinants shared by commensal and pathogenic streptococci.