R. Fontana et al., OVERPRODUCTION OF A LOW-AFFINITY PENICILLIN-BINDING PROTEIN AND HIGH-LEVEL AMPICILLIN RESISTANCE IN ENTEROCOCCUS-FAECIUM, Antimicrobial agents and chemotherapy, 38(9), 1994, pp. 1980-1983
Five ampicillin-resistant clinical isolates of Enterococcus faecium we
re analyzed for a correlation between overproduction of the low-affini
ty penicillin-binding protein (PBP 5) and the level of ampicillin resi
stance. Comparison was made with one susceptible clinical isolate and
its ampicillin-resistant derivative obtained in the laboratory by sele
ction with increasing concentrations of penicillin. Overproduction of
the low-affinity PBP relative to the susceptible isolate was noted in
moderately resistant strains (MIC, 32 mu g/ml) but not in highly resis
tant strains (MIC, 128 mu g/ml). Polyclonal antibodies specifically re
acting with the low-affinity PBP of Enterococcus hirae, Enterococcus f
aecalis, and Enterococcus faecium (M. Ligozzi, M. Aldegheri, S. C. Pre
dari, and R. Fontana, FEMS Microbiol. Lett. 83:335-340, 1991) were use
d to determine the amount of this PBP in the E. faecium isolates. In a
ll strains, the antibody preparation reacted with a membrane protein o
f the same molecular mass as PBP 5. The amount of this protein was ver
y small in the susceptible strain but large in all of the resistant st
rains. These results suggest that the highly resistant strains also ov
erproduced the low-affinity PBP, which, compared with PBP 5 of moderat
ely resistant strains, appeared to be modified in its penicillin-bindi
ng capability.