Multiple changes of penicillin-binding proteins in penicillin-resistant clinical isolates of Streptococcus pneumoniae

Abstract

Penicillin-binding properties and characteristics of penicillin-binding proteins (PBP) were investigated in several clinical isolates of S. pneumoniae differing in their susceptibilities to penicillin (minimal inhibitory concentration [MIC], 0.03-0.5 .mu.g/ml) and compared with the penicillin-susceptible strain R36A (MIC, 0.07 .mu.g/ml). Several changes accompanied the development of resistance: the relative affinity to penicillin of whole cells, isolated membranes and 2 major PBP after in vivo or in vitro labeling decreased (with increasing resistance). One additional PBP (2'') appeared in 4 of 5 relatively resistant strains with an MIC of 0.25 .mu.g/ml and higher. PBP 3 maintained the same high affinity toward penicillin in all strains under all labeling conditions.