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Inactivation of Escherichia coli penicillin-binding proteins by human neutrophils
R M Rakita1, B R Michel, H Rosen
1Department of Internal Medicine, University of Texas Medical School, Houston.
Abstract:
Neutrophils use a variety of microbicidal mechanisms in their role as one of the primary arms of the human host defense system. We have previously observed that a cell-free system containing myeloperoxidase (MPO), one of the major components of the neutrophil's oxidative antimicrobial systems, inactivated microbial penicillin-binding proteins (PBPs), which mediate the formation of the peptidoglycan layer of eubacterial cell walls. This is a potentially important mechanism of MPO-mediated bacterial toxicity. Since numerous other microbicidal systems, both oxidative and nonoxidative, are used by whole neutrophils, we investigated the effect of intact neutrophils on Escherichia coli PBPs. Penicillin binding activity was progressively reduced by neutrophil exposure for all PBPs. Loss of penicillin binding activity correlated well with loss of microbial viability for almost all PBPs. Azide-treated neutrophils, MPO-deficient neutrophils, and chronic granulomatous disease neutrophils inactivated E. coli PBPs in a manner similar to that of normal neutrophils, suggesting that MPO-independent, and even oxygen-independent, microbicidal systems are also involved in inactivation of PBPs. PBP inactivation, an antimicrobial strategy used by beta-lactam-producing molds (and now by physicians), may be an important microbicidal mechanism used by human neutrophils.
Insights
Human neutrophils inactivate bacterial penicillin-binding proteins (PBPs), essential for cell wall formation. This inactivation correlates with bacterial death, indicating a key role for neutrophils in host defense against microbes.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Neutrophils are crucial for host defense, employing diverse microbicidal mechanisms.
- Myeloperoxidase (MPO) is a key component of neutrophil oxidative antimicrobial systems.
- Previous studies showed MPO inactivates microbial penicillin-binding proteins (PBPs).
Purpose of the Study:
- To investigate the effect of intact neutrophils on Escherichia coli PBPs.
- To determine if MPO-independent or oxygen-independent mechanisms contribute to PBP inactivation.
Main Methods:
- Exposure of Escherichia coli to intact human neutrophils.
- Assay of penicillin binding activity of E. coli PBPs.
- Correlation of PBP inactivation with microbial viability.
- Testing of azide-treated, MPO-deficient, and chronic granulomatous disease neutrophils.
Main Results:
- Intact neutrophils progressively reduced penicillin binding activity of all E. coli PBPs.
- Loss of penicillin binding activity correlated with decreased microbial viability.
- MPO-deficient and azide-treated neutrophils also inactivated E. coli PBPs, indicating MPO-independent mechanisms.
- Chronic granulomatous disease neutrophils also inactivated PBPs, suggesting oxygen-independent pathways are involved.
Conclusions:
- Human neutrophils utilize both MPO-dependent and MPO-independent mechanisms to inactivate bacterial PBPs.
- Oxygen-independent microbicidal systems also contribute to PBP inactivation.
- PBP inactivation is a significant microbicidal mechanism employed by human neutrophils, analogous to beta-lactam antibiotics.