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Overproduction of a low-affinity penicillin-binding protein and high-level ampicillin resistance in Enterococcus
R Fontana1, M Aldegheri, M Ligozzi
1Instituto di Microbiologia, Università di Verona, Italy.
Abstract:
Five ampicillin-resistant clinical isolates of Enterococcus faecium were analyzed for a correlation between overproduction of the low-affinity penicillin-binding protein (PBP 5) and the level of ampicillin resistance. Comparison was made with one susceptible clinical isolate and its ampicillin-resistant derivative obtained in the laboratory by selection with increasing concentrations of penicillin. Overproduction of the low-affinity PBP relative to the susceptible isolate was noted in moderately resistant strains (MIC, 32 micrograms/ml) but not in highly resistant strains (MIC, 128 micrograms/ml). Polyclonal antibodies specifically reacting with the low-affinity PBP of Enterococcus hirae, Enterococcus faecalis, and Enterococcus faecium (M. Ligozzi, M. Aldegheri, S. C. Predari, and R. Fontana, FEMS Microbiol. Lett. 83:335-340, 1991) were used to determine the amount of this PBP in the E. faecium isolates. In all strains, the antibody preparation reacted with a membrane protein of the same molecular mass as PBP 5. The amount of this protein was very small in the susceptible strain but large in all of the resistant strains. These results suggest that the highly resistant strains also overproduced the low-affinity PBP, which, compared with PBP 5 of moderately resistant strains, appeared to be modified in its penicillin-binding capability.
Insights
Ampicillin resistance in Enterococcus faecium correlates with overproduction of penicillin-binding protein 5 (PBP 5). Highly resistant strains show modified PBP 5, suggesting altered penicillin-binding capabilities.
Area of Science:
- Microbiology
- Molecular Biology
- Antibiotic Resistance
Background:
- Enterococcus faecium is a significant cause of nosocomial infections.
- Ampicillin resistance in E. faecium is a growing clinical concern.
- Penicillin-binding proteins (PBPs) are key targets for beta-lactam antibiotics.
Purpose of the Study:
- To investigate the correlation between ampicillin resistance levels and the overproduction of low-affinity penicillin-binding protein 5 (PBP 5) in clinical isolates of Enterococcus faecium.
- To compare PBP 5 levels in ampicillin-susceptible and resistant strains, including laboratory-derived resistant mutants.
Main Methods:
- Analysis of five ampicillin-resistant clinical isolates of Enterococcus faecium.
- Comparison with one susceptible isolate and its ampicillin-resistant derivative.
- Use of polyclonal antibodies specific to low-affinity PBP to quantify PBP 5 levels in E. faecium isolates.
Main Results:
- Overproduction of low-affinity PBP was observed in moderately resistant strains (MIC, 32 µg/mL).
- Highly resistant strains (MIC, 128 µg/mL) also showed significant amounts of PBP 5, suggesting overproduction.
- Antibody reactions confirmed the presence of a membrane protein identical in mass to PBP 5 in all strains, with varying amounts.
Conclusions:
- Overproduction of low-affinity PBP 5 is associated with ampicillin resistance in Enterococcus faecium.
- Highly resistant strains may possess a modified PBP 5 with altered penicillin-binding capabilities compared to moderately resistant strains.
- These findings highlight the role of PBP 5 alterations in the development of high-level ampicillin resistance in E. faecium.