Resistance to β-lactam antibiotics by re-modelling the active site of an E. coli penicillin-binding protein

Abstract

The β-lactam antibiotics kill bacteria by inhibiting a set of penicillin-binding proteins (PBPs) that catalyse the final stages of peptidoglycan synthesis^1,2. In some bacteria the development of intrinsic resistance to β-lactam antibiotics by the reduction in the affinity of PBPs causes serious clinical problems^1,3–11. The introduction of β-lactam antibiotics that are resistant to hydrolysis by β-lactamases may also result in the emergence of intrinsic resistance among the Enterobacteriaceae¹. The clinical problems that would arise from the emergence of resistant PBPs in enterobacteria have led us to examine the ease with which Escherichia coli can gain resistance to β-lactams by the production of altered PBPs. The development of resistant PBPs also provides an interesting example of enzyme evolution, since it requires a subtle re-modelling of the enzyme active centre so that it retains affinity for its peptide substrate but excludes the structurally analogous^2,12,13 β-lactam antibiotics. We show here that only four amino-acid substitutions need to be introduced into PBP 3 of E. coli to produce a strain possessing substantial levels of resistance to a wide variety of cephalosporins. We also show that transfer of the gene encoding the resistant PBP 3 from the chromosome to a plasmid could result in the spread of intrinsic resistance not only to other strains of E. coli but also to other enterobacterial species.