Shifting of the penicillin binding proteins that are the target for inhibition by beta-lactams as a likely mechanism of resistance to antibiotics during therapy.

The penicillin binding proteins (PBPs) that in Streptococcus faecium are the targets for inhibitory activity of beta-lactam antibiotics were analyzed both in cells growing at their fastest and at reduced rates. It was found that while under the former conditions the PBPs showed the highest affinity for penicillin, under the latter the target is shifted to PBP (PBP5) that has a very low affinity for penicillin and other beta-lactams. The possibility that conditions met by Enterococci in human infections cause a shifting of the penicillin target and the possible role of such shifting in resistance to beta-lactams during therapy are discussed.