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Petersiel N, Giulieri S, Daniel DS, Fan SH, Ersoy SC, Davis JS, Bayer AS, Howden BP, Tong SYC. Genomic investigation and clinical correlates of the in vitro β-lactam: NaHCO 3 responsiveness phenotype among methicillin-resistant Staphylococcus aureus isolates from a randomized clinical trial. Antimicrob Agents Chemother 2024; 68:e0021824. [PMID: 38837393 PMCID: PMC11232399 DOI: 10.1128/aac.00218-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Accepted: 05/12/2024] [Indexed: 06/07/2024] Open
Abstract
NaHCO3 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 NaHCO3. NaHCO3 responsiveness correlated with treatment response to β-lactams in an endocarditis animal model. We investigated whether treatment of NaHCO3-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 NaHCO3. Isolates exhibiting ≥4-fold decrease in the MIC to cefazolin or oxacillin in the presence of NaHCO3 were considered "NaHCO3-responsive" to that agent. We compared the rate of persistent bacteremia among participants who had infections caused by NaHCO3-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 NaHCO3-responsive to cefazolin and oxacillin, respectively. The NaHCO3-responsive phenotype was significantly associated with sequence type 93, SCCmec 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 NaHCO3-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-NaHCO3-responsive phenotype were associated with distinctive genetic signatures, but not with a shorter duration of bacteremia among those treated with a β-lactam.
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Affiliation(s)
- Neta Petersiel
- Victorian Infectious Diseases Service, The Royal Melbourne Hospital, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
- Department of Infectious Diseases, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Stefano Giulieri
- Victorian Infectious Diseases Service, The Royal Melbourne Hospital, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Diane S Daniel
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
- Microbiological Diagnostic Unit Public Health Laboratory, Department of Microbiology and Immunology, University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Sook-Ha Fan
- The Lundquist Institute for Biomedical Innovation, Torrance, California, USA
| | - Selvi C Ersoy
- The Lundquist Institute for Biomedical Innovation, Torrance, California, USA
| | - Joshua S Davis
- Menzies School of Health Research and Charles Darwin University, Darwin, Northern Territory, Australia
- Department of Infectious Diseases, John Hunter Hospital, Newcastle, New South Wales, Australia
| | - Arnold S Bayer
- The Lundquist Institute for Biomedical Innovation, Torrance, California, USA
- The Geffen School of Medicine, University of California, Los Angeles, California, USA
| | - Benjamin P Howden
- Department of Microbiology and Immunology, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
- Microbiological Diagnostic Unit Public Health Laboratory, Department of Microbiology and Immunology, University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
- Centre for Pathogen Genomics, The University of Melbourne, Melbourne, Victoria, Australia
- Department of Infectious Diseases, Austin Health, Heidelberg, Victoria, Australia
| | - Steven Y C Tong
- Victorian Infectious Diseases Service, The Royal Melbourne Hospital, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
- Department of Infectious Diseases, The University of Melbourne, The Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
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Hosseini H, Abdollahzadeh E, Pilevar Z. Addition of lime juice and NaCl to minced seafood may stimulate the expression of Listeria monocytogenes virulence, adhesion, and stress response genes. Food Sci Nutr 2024; 12:4615-4622. [PMID: 39055235 PMCID: PMC11266898 DOI: 10.1002/fsn3.4064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 01/06/2024] [Accepted: 02/21/2024] [Indexed: 07/27/2024] Open
Abstract
Listeria monocytogenes is a ubiquitous opportunistic bacterium responsible for deadly listeriosis outbreaks. This pathogen has been recognized as a significant food-borne pathogen in seafood products. The present study aimed to investigate the transcript levels of virulence, adhesion, and stress response genes of L. monocytogenes upon exposure to sublethal levels of lime juice and NaCl in shrimp matrix. For this purpose, minced and broth shrimp samples (control, 2% NaCl, 5% NaCl, 25 μL/mL lime, and 50 μL/mL lime, as well as 2% NaCl+25 μL/mL lime) were inoculated with approximately 107 CFU/g or ml of L. monocytogenes, and subsequently, the samples were stored at 12°C or 37°C. For the minced samples, the transcription of one stress-related (sigB), two adhesion (imo1634 and imo1847), and four virulence (hly, prf, intA, and plc) genes was assessed by RT-qPCR after different storage times (0 and 48 h). Results showed that the transcript levels of sigB, imo1847, and imo1634 genes increased with increasing storage temperatures of shrimp broth (12°C to 37°C). At the beginning, the transcription of the studied genes decreased in all treatments of minced shrimp; however, after 48 h of storage at 12°C, the transcript levels of hly, prf, imo1847, imo1634, and intA genes were significantly upregulated up to 0.5-9 log2 fold-change in all treatments compared to the control group (p < .05). These results highlight that the survived L. monocytogenes after exposure to moderate salt content or lime juice could represent enhanced virulence and adhesion capabilities, posing a significant public health risk.
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Affiliation(s)
- Hedayat Hosseini
- Department of Food Science and Technology, National Nutrition and Food Technology Research Institute, Faculty of Nutrition Sciences and Food TechnoloyShahid Beheshti University of Medical SciencesTehranIran
| | - Esmail Abdollahzadeh
- International Sturgeon Research Institute, Iranian Fisheries Science Research Institute, Agricultural ResearchEducation and Extension Organization (AREEO)RashtIran
| | - Zahra Pilevar
- School of HealthArak University of Medical SciencesArakIran
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Ersoy SC, Proctor RA, Rose WE, Abdelhady W, Fan SH, Madrigal SL, Elsayed AM, Chambers HF, Sobral RG, Bayer AS. Sensitizing methicillin-resistant Staphylococcus aureus (MRSA) to cefuroxime: the synergic effect of bicarbonate and the wall teichoic acid inhibitor ticlopidine. Antimicrob Agents Chemother 2024; 68:e0162723. [PMID: 38349162 PMCID: PMC10916381 DOI: 10.1128/aac.01627-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Accepted: 01/18/2024] [Indexed: 03/07/2024] Open
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) strains are a major challenge for clinicians due, in part, to their resistance to most β-lactams, the first-line treatment for methicillin-susceptible S. aureus. A phenotype termed "NaHCO3-responsiveness" has been identified, wherein many clinical MRSA isolates are rendered susceptible to standard-of-care β-lactams in the presence of physiologically relevant concentrations of NaHCO3, in vitro and ex vivo; moreover, such "NaHCO3-responsive" isolates can be effectively cleared by β-lactams from target tissues in experimental infective endocarditis (IE). One mechanistic impact of NaHCO3 exposure on NaHCO3-responsive MRSA is to repress WTA synthesis. This NaHCO3 effect mimics the phenotype of tarO-deficient MRSA, including sensitization to the PBP2-targeting β-lactam, cefuroxime (CFX). Herein, we further investigated the impacts of NaHCO3 exposure on CFX susceptibility in the presence and absence of a WTA synthesis inhibitor, ticlopidine (TCP), in a collection of clinical MRSA isolates from skin and soft tissue infections (SSTI) and bloodstream infections (BSI). NaHCO3 and/or TCP enhanced susceptibility to CFX in vitro, by both minimum inhibitor concentration (MIC) and time-kill assays, as well as in an ex vivo simulated endocarditis vegetations (SEV) model, in NaHCO3-responsive MRSA. Furthermore, in experimental IE (presumably in the presence of endogenous NaHCO3), pre-exposure to TCP prior to infection sensitized the NaHCO3-responsive MRSA strain (but not the non-responsive strain) to enhanced clearances by CFX in target tissues. These data support the notion that NaHCO3 is acting similarly to WTA synthesis inhibitors, and that such inhibitors have potential translational applications in the treatment of certain MRSA strains in conjunction with specific β-lactam agents.
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Affiliation(s)
- Selvi C. Ersoy
- The Lundquist Institute for Biomedical Innovations at Harbor-UCLA Medical Center, Torrance, California, USA
| | - Richard A. Proctor
- Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
- Department of Medical Microbiology and Immunology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Warren E. Rose
- School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Wessam Abdelhady
- The Lundquist Institute for Biomedical Innovations at Harbor-UCLA Medical Center, Torrance, California, USA
| | - Sook-Ha Fan
- The Lundquist Institute for Biomedical Innovations at Harbor-UCLA Medical Center, Torrance, California, USA
| | | | - Ahmed M. Elsayed
- The Lundquist Institute for Biomedical Innovations at Harbor-UCLA Medical Center, Torrance, California, USA
| | - Henry F. Chambers
- University of California-San Francisco School of Medicine, San Francisco, California, USA
| | - Rita G. Sobral
- Laboratory of Molecular Microbiology of Bacterial Pathogens, UCIBIO, Applied Molecular Biosciences Unit, Department of Life Sciences, Nova School of Science and Technology, Universidade Nova de Lisboa, Caparica, Portugal
- Associate Laboratory i4HB, Institute for Health and Bioeconomy, Nova School of Science and Technology, Universidade Nova de Lisboa, Caparica, Portugal
| | - Arnold S. Bayer
- The Lundquist Institute for Biomedical Innovations at Harbor-UCLA Medical Center, Torrance, California, USA
- David Geffen School of Medicine at UCLA, Los Angeles, California, USA
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Sakoulas G, Nizet V. Measuring beta-lactam minimum inhibitory concentrations in Staphylococcus aureus in the clinical microbiology laboratory: pinning the tail on the donkey. J Clin Microbiol 2024; 62:e0036623. [PMID: 37966224 PMCID: PMC10793257 DOI: 10.1128/jcm.00366-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2023] Open
Abstract
Significant shortcomings have been identified in standard methods of susceptibility testing in bacteriological media, not only because the media fails to recapitulate the in vivo environment, but susceptibility testing itself fails to capture sub-MIC effects that significantly attenuate bacterial virulence properties. Until susceptibility testing conditions better recapitulate the in vivo environment, attempts to establish the quantitative relevance of beta-lactam MIC using current clinical microbiology standards in Staphylococcus aureus infections will likely prove unsuccessful.
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Affiliation(s)
- George Sakoulas
- Sharp Rees-Stealy Medical Group, San Diego, California, USA
- UCSD School of Medicine, La Jolla, California, USA
| | - Victor Nizet
- UCSD School of Medicine, La Jolla, California, USA
- Skaggs School of Pharmacy, UCSD School of Medicine, La Jolla, California, USA
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Fan SH, Proctor RA, Ersoy SC, Manna AC, Cheung AL, Götz F, Chambers HF, Bayer AS. Role of the NaHCO 3 Transporter MpsABC in the NaHCO 3-β-Lactam-Responsive Phenotype in Methicillin-Resistant Staphylococcus aureus. Microbiol Spectr 2023; 11:e0014123. [PMID: 37102972 PMCID: PMC10269494 DOI: 10.1128/spectrum.00141-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Accepted: 04/12/2023] [Indexed: 04/28/2023] Open
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) infections are an increasing concern due to their intrinsic resistance to most standard-of-care β-lactam antibiotics. Recent studies of clinical isolates have documented a novel phenotype, termed NaHCO3 responsiveness, in which a substantial proportion of MRSA strains exhibit enhanced susceptibility to β-lactams such as cefazolin and oxacillin in the presence of NaHCO3. A bicarbonate transporter, MpsAB (membrane potential-generating system), was recently found in S. aureus, where it plays a role in concentrating NaHCO3 for anaplerotic pathways. Here, we investigated the role of MpsAB in mediating the NaHCO3 responsiveness phenotype. Radiolabeled NaH14CO3 uptake profiling revealed significantly higher accumulation in NaHCO3-responsive vs nonresponsive MRSA strains when grown in ambient air. In contrast, under 5% CO2 conditions, NaHCO3-responsive (but not nonresponsive) strains exhibited repressed uptake. Oxacillin MICs were measured in four prototype strains and their mpsABC deletion mutants in the presence of NaHCO3 supplementation under 5% CO2 conditions. NaHCO3-mediated reductions in oxacillin MICs were observed in the responsive parental strains but not in mpsABC deletion mutants. No significant impact on oxacillin MICs was observed in the nonresponsive strains under the same conditions. Transcriptional and translational studies were carried out using both quantitative reverse transcription-PCR (qRT-PCR) and mpsA-green fluorescent protein (GFP) fusion constructs; these investigations showed that mpsA expression and translation were significantly upregulated during mid-exponential-phase growth in oxacillin-NaHCO3-supplemented medium in responsive versus nonresponsive strains. Taken together, these data show that the NaHCO3 transporter MpsABC is a key contributor to the NaHCO3-β-lactam responsiveness phenotype in MRSA. IMPORTANCE MRSA infections are increasingly difficult to treat, due in part to their resistance to most β-lactam antibiotics. A novel and relatively common phenotype, termed NaHCO3 responsiveness, has been identified in which MRSA strains show increased susceptibility in vitro and in vivo to β-lactams in the presence of NaHCO3. A recently described S. aureus NaHCO3 transporter, MpsAB, is involved in intracellular NaHCO3 concentration for anaplerotic pathways. We investigated the role of MpsAB in mediating the NaHCO3 responsiveness phenotype in four prototype MRSA strains (two responsive and two nonresponsive). We demonstrated that MpsABC is an important contributor to the NaHCO3-β-lactam responsiveness phenotype. Our study adds to the growing body of well-defined characteristics of this novel phenotype, which could potentially translate to alternative targets for MRSA treatment using β-lactams.
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Affiliation(s)
- Sook-Ha Fan
- The Lundquist Institute, Torrance, California, USA
| | - Richard A. Proctor
- Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
- Department of Medical Microbiology/Immunology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | | | - Adhar C. Manna
- Department of Microbiology & Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA
| | - Ambrose L. Cheung
- Department of Microbiology & Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA
| | - Friedrich Götz
- Microbial Genetics, Interfaculty Institute of Microbiology and Infection Medicine Tübingen, University of Tübingen, Germany
| | | | - Arnold S. Bayer
- The Lundquist Institute, Torrance, California, USA
- Geffen School of Medicine at UCLA, Los Angeles, California, USA
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Ersoy SC, Gonçalves B, Cavaco G, Manna AC, Sobral RG, Nast CC, Proctor RA, Chambers HF, Cheung A, Bayer AS. Influence of Sodium Bicarbonate on Wall Teichoic Acid Synthesis and β-Lactam Sensitization in NaHCO 3-Responsive and Nonresponsive Methicillin-Resistant Staphylococcus aureus. Microbiol Spectr 2022; 10:e0342222. [PMID: 36377886 PMCID: PMC9769754 DOI: 10.1128/spectrum.03422-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 10/13/2022] [Indexed: 11/16/2022] Open
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) strains pose major treatment challenges due to their innate resistance to most β-lactams under standard in vitro antimicrobial susceptibility testing conditions. A novel phenotype among MRSA, termed "NaHCO3 responsiveness," where certain strains display increased susceptibility to β-lactams in the presence of NaHCO3, has been identified among a relatively large proportion of MRSA isolates. One underlying mechanism of NaHCO3 responsiveness appears to be related to decreased expression and altered functionality of several genes and proteins involved in cell wall synthesis and maturation. Here, we studied the impact of NaHCO3 on wall teichoic acid (WTA) synthesis, a process intimately linked to peptidoglycan (PG) synthesis and functionality, in NaHCO3-responsive versus -nonresponsive MRSA isolates. NaHCO3 sensitized responsive MRSA strains to cefuroxime, a specific penicillin-binding protein 2 (PBP2)-inhibitory β-lactam known to synergize with early WTA synthesis inhibitors (e.g., ticlopidine). Combining cefuroxime with ticlopidine with or without NaHCO3 suggested that these latter two agents target the same step in WTA synthesis. Further, NaHCO3 decreased the abundance and molecular weight of WTA only in responsive strains. Additionally, NaHCO3 stimulated increased autolysis and aberrant cell division in responsive strains, two phenotypes associated with disruption of WTA synthesis. Of note, studies of key genes involved in the WTA biosynthetic pathway (e.g., tarO, tarG, dltA, and fmtA) indicated that the inhibitory impact of NaHCO3 on WTA biosynthesis in responsive strains likely occurred posttranslationally. IMPORTANCE MRSA is generally viewed as resistant to standard β-lactam antibiotics. However, a NaHCO3-responsive phenotype is observed in a substantial proportion of clinical MRSA strains in vitro, i.e., isolates which demonstrate enhanced susceptibility to standard β-lactam antibiotics (e.g., oxacillin) in the presence of NaHCO3. This phenotype correlates with increased MRSA clearance in vivo by standard β-lactam antibiotics, suggesting that patients with infections caused by such MRSA strains might be amenable to treatment with β-lactams. The mechanism(s) behind this phenotype is not fully understood but appears to involve mecA-PBP2a production and maturation axes. Our study adds significantly to this body of knowledge in terms of additional mechanistic targets of NaHCO3 in selected MRSA strains. This investigation demonstrates that NaHCO3 has direct impacts on S. aureus wall teichoic acid biosynthesis in NaHCO3-responsive MRSA. These findings provide an additional target for new agents being designed to synergistically kill MRSA using β-lactam antibiotics.
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Affiliation(s)
| | - Barbara Gonçalves
- Laboratory of Molecular Microbiology of Bacterial Pathogens, UCIBIO, Applied Molecular Biosciences Unit, Department of Life Sciences, Nova School of Science and Technology, Universidade Nova de Lisboa, Caparica, Portugal
- Associate Laboratory i4HB, Institute for Health and Bioeconomy, Nova School of Science and Technology, Universidade Nova de Lisboa, Caparica, Portugal
| | - Gonçalo Cavaco
- Laboratory of Molecular Microbiology of Bacterial Pathogens, UCIBIO, Applied Molecular Biosciences Unit, Department of Life Sciences, Nova School of Science and Technology, Universidade Nova de Lisboa, Caparica, Portugal
- Associate Laboratory i4HB, Institute for Health and Bioeconomy, Nova School of Science and Technology, Universidade Nova de Lisboa, Caparica, Portugal
| | - Adhar C. Manna
- Department of Microbiology & Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA
| | - Rita G. Sobral
- Laboratory of Molecular Microbiology of Bacterial Pathogens, UCIBIO, Applied Molecular Biosciences Unit, Department of Life Sciences, Nova School of Science and Technology, Universidade Nova de Lisboa, Caparica, Portugal
- Associate Laboratory i4HB, Institute for Health and Bioeconomy, Nova School of Science and Technology, Universidade Nova de Lisboa, Caparica, Portugal
| | - Cynthia C. Nast
- Cedars-Sinai Medical Center, Los Angeles, California, USA
- Geffen School of Medicine at UCLA, Los Angeles, California, USA
| | - Richard A. Proctor
- Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
- Department of Medical Microbiology/Immunology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | | | - Ambrose Cheung
- Department of Microbiology & Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA
| | - Arnold S. Bayer
- The Lundquist Institute, Torrance, California, USA
- Geffen School of Medicine at UCLA, Los Angeles, California, USA
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The NaHCO 3-Responsive Phenotype in Methicillin-Resistant Staphylococcus aureus (MRSA) Is Influenced by mecA Genotype. Antimicrob Agents Chemother 2022; 66:e0025222. [PMID: 35575577 PMCID: PMC9211399 DOI: 10.1128/aac.00252-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) strains are a leading cause of many invasive clinical syndromes, and pose treatment difficulties due to their in vitro resistance to most β-lactams on standard laboratory testing. A novel phenotype frequently identified in MRSA strains, termed ‘NaHCO3-responsiveness’, is a property whereby strains are susceptible in vitro to many β-lactams in the presence of NaHCO3. Specific mecA genotypes, repression of mecA/PBP2a expression and perturbed maturation of PBP2a by NaHCO3 have all been associated with this phenotype. The aim of this study was to define the relationship between specific mecA genotypes and PBP2a substitutions, on the one hand, with NaHCO3-responsiveness in vitro. Mutations were made in the mecA ribosomal binding site (RBS -7) and at amino acid position 246 of its coding region in parental strains MW2 (NaHCO3-responsive) and C36 (NaHCO3- nonresponsive) to generate ‘swap’ variants, each harboring the other’s mecA-RBS/coding region genotypes. Successful swaps were confirmed by both sequencing, as well as predicted swap of in vitro penicillin-clavulanate susceptibility phenotypes. MW2 swap variants harboring the nonresponsive mecA genotypes became NaHCO3-nonresponsive (resistant to the β-lactam, oxacillin [OXA]), in the presence of NaHCO3. Moreover, these swap variants had lost NaHCO3-mediated repression of mecA/PBP2a expression. In contrast, C36 swap variants harboring the NaHCO3-responsive mecA genotypes remained NaHCO3-nonresponsive phenotypically, and still exhibited nonrepressible mecA/PBP2a expression. These data demonstrate that in addition to the mecA genotype, NaHCO3-responsiveness may also depend on strain-specific genetic backgrounds.
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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 (Basel) 2022; 11:antibiotics11040462. [PMID: 35453214 PMCID: PMC9028190 DOI: 10.3390/antibiotics11040462] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 03/23/2022] [Accepted: 03/26/2022] [Indexed: 12/13/2022] Open
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.
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Affiliation(s)
- Selvi C. Ersoy
- The Lundquist Institute for Biomedical Innovation, Harbor-UCLA Medical Center, Torrance, CA 90502, USA; (S.C.E.); (L.C.C.); (M.R.Y.)
| | - Liana C. Chan
- The Lundquist Institute for Biomedical Innovation, Harbor-UCLA Medical Center, Torrance, CA 90502, USA; (S.C.E.); (L.C.C.); (M.R.Y.)
- David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
- Division of Infectious Diseases, Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA 90502, USA
- Division of Molecular Medicine, Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA 90502, USA
| | - Michael R. Yeaman
- The Lundquist Institute for Biomedical Innovation, Harbor-UCLA Medical Center, Torrance, CA 90502, USA; (S.C.E.); (L.C.C.); (M.R.Y.)
- David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
- Division of Infectious Diseases, Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA 90502, USA
- Division of Molecular Medicine, Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA 90502, USA
| | - Henry F. Chambers
- School of Medicine, University of California-San Francisco (UCSF), San Francisco, CA 94143, USA;
| | - Richard A. Proctor
- Departments of Medicine and Medical Microbiology/Immunology, School of Medicine and Public Health, University of Wisconsin, Madison, WI 53715, USA;
| | - Kevin C. Ludwig
- Institute for Pharmaceutical Microbiology, University Hospital Bonn, University of Bonn, D-53113 Bonn, Germany; (K.C.L.); (T.S.)
| | - Tanja Schneider
- Institute for Pharmaceutical Microbiology, University Hospital Bonn, University of Bonn, D-53113 Bonn, Germany; (K.C.L.); (T.S.)
| | - Adhar C. Manna
- Department of Microbiology & Immunology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA; (A.C.M.); (A.C.)
| | - Ambrose Cheung
- Department of Microbiology & Immunology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA; (A.C.M.); (A.C.)
| | - Arnold S. Bayer
- The Lundquist Institute for Biomedical Innovation, Harbor-UCLA Medical Center, Torrance, CA 90502, USA; (S.C.E.); (L.C.C.); (M.R.Y.)
- David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
- Division of Infectious Diseases, Department of Medicine, Harbor-UCLA Medical Center, Torrance, CA 90502, USA
- Correspondence: ; Tel.: +1-310-222-6422
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