Identification and characterization of the penicillin-binding protein 2a of Streptococcus pneumoniae and its possible role in resistance to beta-lactam antibiotics

To further understand the role of penicillin-binding protein 2a (PBP 2a) of Streptococcus pneumoniae in penicillin resistance, we confirmed the identi ty of the protein as PBP 2a. The PBP 2a protein migrated electrophoreticall y to a position corresponding to that of PBP 2x, PBP 2a, and PBP 2b of S. p neumoniae and was absent in a pbp2a insertional mutant of S. pneumoniae. We found that the affinities of PBP 2a for penicillins were lower than for ce phalosporins and a carbapenem. When compared with other S. pneumoniae PBPs, PBP 2a exhibited lower affinities for p-lactam antibiotics, especially pen icillins. Therefore, PBP 2a is a low-affinity PBP for beta-lactam antibioti cs in S. pneumoniae.