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Penicillin-binding protein 3 of Listeria monocytogenes as the primary lethal target for beta-lactams
M F Vicente1, J C Pérez-Dáz, F Baquero
1Servicio de Microbiología, Hospital Ramon y Cajal, Madrid, Spain.
Abstract:
Penicillin-binding proteins (PBPs) of Listeria monocytogenes were detected by their ability to bind to [2,3-3H]benzylpenicillin. Five proteins with Mrs of 95,000, 84,000, 80,000, 76,000, and 49,000 were detected. PBPs 1 to 4 had a high affinity for [2,3-3H]benzylpenicillin and were relatively scarce (80 to 150 molecules per cell). In contrast, PBP 5 was more abundant (600 molecules per cell) but had a low affinity for [2,3-3H]benzylpenicillin. L. monocytogenes has a relatively high natural resistance to cephalosporins. Competition experiments showed that cephalosporins bound very poorly to PBP 3 but were good inhibitors of PBPs 1, 2, and 4, which were completely blocked at concentrations well below the MIC. Analysis of a spontaneous imipenem-resistant mutant revealed that resistance was likely due to an altered PBP 3 with a reduced affinity for [2,3-3H]benzylpenicillin. These results suggest that PBP 3 is a primary lethal target for beta-lactams in L. monocytogenes.
Insights
Penicillin-binding proteins (PBPs) in Listeria monocytogenes were identified. PBP 3 is a key target for beta-lactam antibiotics, as alterations in PBP 3 confer imipenem resistance.
Area of Science:
- Microbiology
- Bacterial Physiology
- Antibiotic Resistance
Background:
- Listeria monocytogenes exhibits natural resistance to cephalosporins.
- Penicillin-binding proteins (PBPs) are crucial targets for beta-lactam antibiotics.
Purpose of the Study:
- To identify and characterize penicillin-binding proteins (PBPs) in Listeria monocytogenes.
- To investigate the role of PBPs in Listeria monocytogenes' resistance to beta-lactam antibiotics.
Main Methods:
- Detection of PBPs using [2,3-3H]benzylpenicillin binding assays.
- Affinity and abundance determination of identified PBPs.
- Competition assays with cephalosporins and analysis of imipenem-resistant mutants.
Main Results:
- Five PBPs (95, 84, 80, 76, and 49 kDa) were detected in Listeria monocytogenes.
- PBPs 1-4 showed high affinity and low abundance, while PBP 5 was abundant with low affinity.
- Cephalosporins poorly inhibited PBP 3 but effectively blocked PBPs 1-4.
- An imipenem-resistant mutant displayed an altered PBP 3 with reduced affinity for benzylpenicillin.
Conclusions:
- PBP 3 is identified as a primary lethal target for beta-lactams in Listeria monocytogenes.
- Alterations in PBP 3 are strongly associated with beta-lactam resistance in this bacterium.