Alterations of Penicillin-Binding Proteins 1A, 2X, and 2B in Streptococcus pneumoniae Isolates for Which Amoxicillin MICs Are Higher than Penicillin MICs

Penicillin-binding proteins (PBPs) of 15 selected penicillin- and amoxicillin-resistant Streptococcus pneumoniae isolates (MICs of 2 to 8 and 8 to 16 microg/ml, respectively) were studied. In addition to typical changes in PBPs 1A and 2X, these strains had 10 unique changes in PBP 2B, including a (618)A-G substitution, which may be the key alteration associated with amoxicillin resistance.