{"doi":"10.3390/antibiotics11040462","title":"Impacts of NaHCO3 on β-Lactam Binding to PBP2a Protein Variants Associated with the NaHCO3-Responsive versus NaHCO3-Non-Responsive Phenotypes","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.","journal":"Antibiotics","year":2022,"id":275087,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":9,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9618,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2022-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":345681,"name":"Liana C. Chan","orcid":"0000-0003-2567-4418","position":1,"is_corresponding":false},{"id":345685,"name":"Michael R. Yeaman","orcid":"0000-0002-9468-5252","position":2,"is_corresponding":false},{"id":232760,"name":"Henry F. Chambers","orcid":"0000-0001-5317-4491","position":3,"is_corresponding":false},{"id":397629,"name":"Richard A. Proctor","orcid":"0000-0003-3011-7958","position":4,"is_corresponding":false},{"id":240946,"name":"Kevin C. Ludwig","orcid":"0000-0003-3534-0729","position":5,"is_corresponding":false},{"id":240949,"name":"Tanja Schneider","orcid":"0000-0001-7269-4716","position":6,"is_corresponding":false},{"id":897436,"name":"Adhar C. Manna","orcid":"0000-0002-4055-2489","position":7,"is_corresponding":false},{"id":502764,"name":"Ambrose L. Cheung","orcid":"0000-0001-5120-3949","position":8,"is_corresponding":false},{"id":397631,"name":"Arnold S. Bayer","orcid":"0000-0003-1968-0192","position":9,"is_corresponding":false},{"id":397628,"name":"Selvi C. Ersoy","orcid":"0000-0002-8792-2061","position":0,"is_corresponding":true}],"reference_count":33,"raw_metadata":null,"created_at":"2026-07-19T00:28:16.928746Z","pmid":"35453214","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}