Detection of Low Affinity Penicillin-Binding Protein Variants in Streptococcus pneumoniae

Penicillin-resistance in Streptococcus pneumoniae is mediated by altered penicillin-target enzymes, the penicillin-binding proteins or PBPs. PBPs interact withβ-lactam antibiotics by forming an active penicilloyl-PBP complex via an active site serine. This complex is enzymatically inactive, and stable enough so that it can be visualized by incubating cells, cell lysates or membrane fractions with radioactive β-lactam, followed by SDS-polyacrylamidegel electrophoresis (PAGE) and fluorography. The increasing frequency of β-lactam resistant isolates necessitates techniques for describing such strains. PBP profile analysis allows the detection of the variation in six proteins simultaneously and thus each PBP profile is basically a fingerprint of the strain, allowing to assign hundreds of isolates into distinct clonal groups (1, 2).