Penicillin-binding proteins in Streptococcus faecalis and S. faecium.

Penicillin-binding proteins (PBPs) of Streptococcus faecalis NCTC 775, S. faecium NCTC 7171 and an isolate of S. faecium (strain 37) highly resistant to beta-lactam antibiotics were visualised by autoradiography. Five PBPs were detected in S. faecalis NCTC 775 and six in S. faecium NCTC 7171. Additional PBPs could not be found in the resistant isolate of S. faecium. The PBP affinities of beta lactams were compared with MIC values. The affinities of PBPs 3 and 4 of S. faecalis NCTC 775 for penicillin G, ampicillin, cefathiamidine, cephaloridine and cephazolin were related to the sensitivity of the strain to these antibiotics as were the affinities of PBPs 4 and 5 in each S. faecium strain for the beta lactams. It is postulated that PBPs 3 and 4 of S. faecalis NCTC 775 and PBPs 4 and 5 of S. faecium are the relevant target enzymes of the test antibiotics. PBPs 4 and 5 of the highly beta-lactam-resistant S. faecium strain 37 showed proportionally low affinities for the five beta lactams compared to that of the less resistant strain S. faecium NCTC 7171. Decreased affinities of PBPs 4 and 5 may account for the resistance in S. faecium strain 37 to beta lactams. The affinities for PBP 1, 2 and 5 in S. faecalis NCTC 775 and PBPs 1, 2, 3 and 6 in S. faecium were not related to the antibiotic sensitivities.