{"doi":"10.1128/aac.00218-24","title":"Genomic investigation and clinical correlates of the <i>in vitro</i> β-lactam: NaHCO <sub>3</sub> responsiveness phenotype among methicillin-resistant <i>Staphylococcus aureus</i> isolates from a randomized clinical trial","abstract":"ABSTRACT NaHCO 3 responsiveness is a novel phenotype where some methicillin-resistant Staphylococcus aureus (MRSA) isolates exhibit significantly lower minimal inhibitory concentrations (MIC) to oxacillin and/or cefazolin in the presence of NaHCO 3 . NaHCO 3 responsiveness correlated with treatment response to β-lactams in an endocarditis animal model. We investigated whether treatment of NaHCO 3 -responsive strains with β-lactams was associated with faster clearance of bacteremia. The CAMERA2 trial (Combination Antibiotics for Methicillin-Resistant Staphylococcus aureus ) randomly assigned participants with MRSA bloodstream infections to standard therapy, or to standard therapy plus an anti-staphylococcal β-lactam (combination therapy). For 117 CAMERA2 MRSA isolates, we determined by broth microdilution the MIC of cefazolin and oxacillin, with and without 44 mM of NaHCO 3 . Isolates exhibiting ≥4-fold decrease in the MIC to cefazolin or oxacillin in the presence of NaHCO 3 were considered “NaHCO 3 -responsive” to that agent. We compared the rate of persistent bacteremia among participants who had infections caused by NaHCO 3 -responsive and non-responsive strains, and that were assigned to combination treatment with a β-lactam. Thirty-one percent (36/117) and 25% (21/85) of MRSA isolates were NaHCO 3 -responsive to cefazolin and oxacillin, respectively. The NaHCO 3 -responsive phenotype was significantly associated with sequence type 93, SCC mec type IVa, and mecA alleles with substitutions in positions −7 and −38 in the regulatory region. Among participants treated with a β-lactam, there was no association between the NaHCO 3 -responsive phenotype and persistent bacteremia (cefazolin, P = 0.82; oxacillin, P = 0.81). In patients from a randomized clinical trial with MRSA bloodstream infection, isolates with an in vitro β-lactam-NaHCO 3 -responsive phenotype were associated with distinctive genetic signatures, but not with a shorter duration of bacteremia among those treated with a β-lactam.","journal":"Antimicrobial Agents and Chemotherapy","year":2024,"id":471164,"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":2,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.964,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2024-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":995562,"name":"Stefano Giulieri","orcid":"0000-0001-5366-1943","position":1,"is_corresponding":false},{"id":1306095,"name":"Diane Daniel","orcid":null,"position":2,"is_corresponding":false},{"id":1130708,"name":"Sook‐Ha Fan","orcid":"0000-0003-0556-238X","position":3,"is_corresponding":false},{"id":397628,"name":"Selvi C. 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