Impacts of NaHCO3 on β-Lactam Binding to PBP2a Protein Variants Associated with the NaHCO3-Responsive versus NaHCO3-Non-Responsive Phenotypes

Ersoy, Selvi C.; Chan, Liana C.; Yeaman, Michael R.; Chambers, Henry F.; Proctor, Richard A.; Ludwig, Kevin C.; Schneider, Tanja; Manna, Adhar C.; Cheung, Ambrose; Bayer, Arnold S.

doi:10.3390/antibiotics11040462

Open AccessArticle

Impacts of NaHCO₃ on β-Lactam Binding to PBP2a Protein Variants Associated with the NaHCO₃-Responsive versus NaHCO₃-Non-Responsive Phenotypes

by

Selvi C. Ersoy

¹

,

Liana C. Chan

^1,2,3,4,

Michael R. Yeaman

^1,2,3,4,

Henry F. Chambers

⁵,

Richard A. Proctor

⁶,

Kevin C. Ludwig

⁷

,

Tanja Schneider

⁷,

Adhar C. Manna

⁸,

Ambrose Cheung

⁸ and

Arnold S. Bayer

^1,2,3,*

¹

The Lundquist Institute for Biomedical Innovation, Harbor-UCLA Medical Center, Torrance, CA 90502, USA

²

David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA

³

Division of Infectious Diseases, Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA 90502, USA

⁴

Division of Molecular Medicine, Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA 90502, USA

⁵

School of Medicine, University of California-San Francisco (UCSF), San Francisco, CA 94143, USA

⁶

Departments of Medicine and Medical Microbiology/Immunology, School of Medicine and Public Health, University of Wisconsin, Madison, WI 53715, USA

⁷

Institute for Pharmaceutical Microbiology, University Hospital Bonn, University of Bonn, D-53113 Bonn, Germany

⁸

Department of Microbiology & Immunology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA

^*

Author to whom correspondence should be addressed.

Antibiotics 2022, 11(4), 462; https://doi.org/10.3390/antibiotics11040462

Submission received: 28 February 2022 / Revised: 23 March 2022 / Accepted: 26 March 2022 / Published: 30 March 2022

(This article belongs to the Special Issue A Themed Issue in Honor of Professor Alexander Tomasz—Outstanding Contributions in the Fields of Antibiotic Resistance and Bacterial Infectious Diseases)

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Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) regulates resistance to β-lactams via preferential production of an alternative penicillin-binding protein (PBP), PBP2a. PBP2a binds many β-lactam antibiotics with less affinity than PBPs which are predominant in methicillin-susceptible (MSSA) strains. A novel, rather frequent in vitro phenotype was recently identified among clinical MRSA bloodstream isolates, termed “NaHCO₃-responsiveness”. This phenotype features β-lactam susceptibility of certain MRSA strains only in the presence of NaHCO₃. Two distinct PBP2a variants, 246G and 246E, have been linked to the NaHCO₃-responsive and NaHCO₃-non-responsive MRSA phenotypes, respectively. To determine the mechanistic impact of PBP2a variants on β-lactam susceptibility, binding profiles of a fluorescent penicillin probe (Bocillin-FL) to each purified PBP2a variant were assessed and compared to whole-cell binding profiles characterized by flow cytometry in the presence vs. absence of NaHCO₃. These investigations revealed that NaHCO₃ differentially influenced the binding of the fluorescent penicillin, Bocillin-FL, to the PBP2a variants, with binding intensity and rate of binding significantly enhanced in the 246G compared to the 246E variant. Of note, the NaHCO₃-β-lactam (oxacillin)-responsive JE2 strain, which natively harbors the 246G variant, had enhanced Bocillin-FL whole-cell binding following exposure to NaHCO₃. This NaHCO₃-mediated increase in whole-cell Bocillin-FL binding was not observed in the NaHCO₃-non-responsive parental strain, COL, which contains the 246E PBP2a variant. Surprisingly, genetic swaps of the mecA coding sites between JE2 and COL did not alter the NaHCO₃-enhanced binding seen in JE2 vs. COL. These data suggest that the non-coding regions of mecA may be involved in NaHCO₃-responsiveness. This investigation also provides strong evidence that the NaHCO₃-responsive phenotype in MRSA may involve NaHCO₃-mediated increases in both initial cell surface β-lactam binding, as well as ultimate PBP2a binding of β-lactams.

Keywords: penicillin-binding proteins; sodium bicarbonate; β-lactams; methicillin-resistant Staphylococcus aureus

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MDPI and ACS Style

Ersoy, S.C.; Chan, L.C.; Yeaman, M.R.; Chambers, H.F.; Proctor, R.A.; Ludwig, K.C.; Schneider, T.; Manna, A.C.; Cheung, A.; Bayer, A.S. Impacts of NaHCO₃ on β-Lactam Binding to PBP2a Protein Variants Associated with the NaHCO₃-Responsive versus NaHCO₃-Non-Responsive Phenotypes. Antibiotics 2022, 11, 462. https://doi.org/10.3390/antibiotics11040462

AMA Style

Ersoy SC, Chan LC, Yeaman MR, Chambers HF, Proctor RA, Ludwig KC, Schneider T, Manna AC, Cheung A, Bayer AS. Impacts of NaHCO₃ on β-Lactam Binding to PBP2a Protein Variants Associated with the NaHCO₃-Responsive versus NaHCO₃-Non-Responsive Phenotypes. Antibiotics. 2022; 11(4):462. https://doi.org/10.3390/antibiotics11040462

Chicago/Turabian Style

Ersoy, Selvi C., Liana C. Chan, Michael R. Yeaman, Henry F. Chambers, Richard A. Proctor, Kevin C. Ludwig, Tanja Schneider, Adhar C. Manna, Ambrose Cheung, and Arnold S. Bayer. 2022. "Impacts of NaHCO₃ on β-Lactam Binding to PBP2a Protein Variants Associated with the NaHCO₃-Responsive versus NaHCO₃-Non-Responsive Phenotypes" Antibiotics 11, no. 4: 462. https://doi.org/10.3390/antibiotics11040462

APA Style

Ersoy, S. C., Chan, L. C., Yeaman, M. R., Chambers, H. F., Proctor, R. A., Ludwig, K. C., Schneider, T., Manna, A. C., Cheung, A., & Bayer, A. S. (2022). Impacts of NaHCO₃ on β-Lactam Binding to PBP2a Protein Variants Associated with the NaHCO₃-Responsive versus NaHCO₃-Non-Responsive Phenotypes. Antibiotics, 11(4), 462. https://doi.org/10.3390/antibiotics11040462

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Impacts of NaHCO₃ on β-Lactam Binding to PBP2a Protein Variants Associated with the NaHCO₃-Responsive versus NaHCO₃-Non-Responsive Phenotypes

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