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- Title
Impacts of NaHCO 3 on β-Lactam Binding to PBP2a Protein Variants Associated with the NaHCO 3 -Responsive versus NaHCO 3 -Non-Responsive Phenotypes.
- Authors
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.
- 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.
- Subjects
OXACILLIN; CARRIER proteins; METHICILLIN-resistant staphylococcus aureus; PENICILLIN-binding proteins; PROTEIN binding; PHENOTYPES
- Publication
Antibiotics (2079-6382), 2022, Vol 11, Issue 4, pN.PAG
- ISSN
2079-6382
- Publication type
Article
- DOI
10.3390/antibiotics11040462