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One or two low affinity penicillin-binding proteins may be responsible for the range of susceptibility of
Abstract:
Three benzylpenicillin-resistant, clinical isolates of Enterococcus faecium (MIC values 16-64 micrograms ml-1) contained six penicillin-binding proteins (PBPs), of which PBP5 was the most abundant and had the lowest affinity for the antibiotic. Four benzylpenicillin-susceptible strains (MIC values 0.031-0.5 microgram ml-1) were obtained as spontaneous derivatives from these above organisms. There were significant decreases in the amounts of PBP5 in each of the derivatives, with the concomitant appearance of a new, higher affinity PBP (5*) in three strains. Increased amounts of PBP5, with no changes in PBP5*, were found in several mutants with intermediate-level benzylpenicillin-resistance (MIC values 1-8 micrograms ml-1) selected from two of the susceptible strains. Examination of 18 other clinical isolates, with a wide range of susceptibilities to benzylpenicillin (MIC values 0.062-128 micrograms ml-1), showed that PBP5* was present in 13 strains, and PBP5 in all of them, but in differing amounts. The results concerning the relative amounts and relative affinities of PBPs 5* and 5 allowed the categorization of the various strains into six groups, within which organisms had somewhat similar susceptibilities to benzylpenicillin.
Insights
Penicillin-binding protein 5 (PBP5) and a novel variant, PBP5*, are key to Enterococcus faecium resistance to benzylpenicillin. Changes in PBP5 and PBP5* amounts and affinities correlate with benzylpenicillin susceptibility levels.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Enterococcus faecium is a significant opportunistic pathogen.
- Antibiotic resistance in E. faecium is a growing clinical concern.
- Penicillin-binding proteins (PBPs) are crucial targets for beta-lactam antibiotics like benzylpenicillin.
Purpose of the Study:
- To investigate the role of penicillin-binding proteins (PBPs), specifically PBP5, in benzylpenicillin resistance in Enterococcus faecium.
- To characterize the relationship between PBP5 expression, a novel PBP5* variant, and varying levels of benzylpenicillin susceptibility.
Main Methods:
- Analysis of penicillin-binding proteins (PBPs) in clinical isolates of Enterococcus faecium with varying benzylpenicillin resistance levels.
- Selection and characterization of spontaneous benzylpenicillin-susceptible and intermediate-resistant mutants.
- Quantification of PBP5 and PBP5* amounts and assessment of their affinities for benzylpenicillin.
Main Results:
- Resistant E. faecium strains possessed abundant PBP5 with low benzylpenicillin affinity.
- Susceptible derivatives showed decreased PBP5 levels and often gained a higher-affinity PBP5*.
- Mutants with intermediate resistance exhibited increased PBP5 levels without PBP5* changes.
- PBP5* was detected in 13 of 18 diverse clinical isolates, correlating with resistance.
Conclusions:
- PBP5 and the novel PBP5* play critical roles in determining benzylpenicillin susceptibility in Enterococcus faecium.
- The relative amounts and affinities of PBP5 and PBP5* can be used to categorize strains based on their benzylpenicillin resistance.
- Understanding these PBP alterations provides insights into mechanisms of antibiotic resistance in E. faecium.