Alterations in MurM, a Cell Wall Muropeptide Branching Enzyme, Increase High-Level Penicillin and Cephalosporin Resistance in Streptococcus pneumoniae

We report that alteration in MurM, an enzyme involved in the biosynthesis of branched-stem cell wall muropeptides, is required for maximal expression of penicillin and cefotaxime resistance in the pneumococcus. Hungarian isolate 3191 (penicillin MIC, 16 μg/ml; cefotaxime MIC, 4 μg/ml) was a source of donor DNA in transformation experiments. Penicillin-binding protein DNA was insufficient to transform recipient strain R6 to full resistance. Further transformation with altered murM DNA was required for full expression of donor penicillin and cefotaxime resistance.